Telex Intercom System 38109 977 User Manual

HANDBOOK OF INTERCOM  
SYSTEMS ENGINEERING  
FIRST EDITION  
38109-977 Preliminary Rev. 4, 3/2002  
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TABLE OF CONTENTS  
i
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ii  
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iii  
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iv  
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vi  
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LIST OF FIGURES  
A comparison of the 9400 Intercom System to the 9500 Intercom System (see inset).  
The 9500 represented a tremendous reduction in physical size. - - - - - - - - - - - - - - - 50  
Use of Source Assignment Panels such as this SAP-1626 allow the  
rapid reconfiguration of PL systems without changing any cables - - - - - - - - - - - - - 58  
A wide variety of keypanel options exist. Here we have a selection of  
RTS™ keypanels that fit a range of needs. Small keypanels such as the  
(A) KP-12LK and (B) WKP-4 provide an interface for those with limited  
keypanel needs. The (G) KP-96-7, a medium sized unit, was the workhorse  
the top of the line keypanel, and can be enhanced through additional options,  
such as the (D) EKP-32 expansion panel, and the (F) LCP-32/16 level control  
panel. The (E) KP-8T is an example of a specialty keypanel that makes use of  
an empty bay in a Tektronix vectorscope. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 66  
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The RadioCom™ BTR-800 System is an outstanding example of the  
next generation of wireless intercom systems. - - - - - - - - - - - - - - - - - - - - - - - - - - -89  
The orientation of the radiator (antenna) determines the polarization,  
and therefore, the orientation of the E and H fields. - - - - - - - - - - - - - - - - - - - - - - -99  
A comparison of the radiation patterns for an Isotropic Radiator  
(theoretical) vs. a Dipole (practical). - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 105  
Figure 3. Block diagram of a medium sized intercom system using two-wire.  
IFB circuits. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 119  
Block diagram of a medium sized intercom system using the Zeus™  
increased to include point-to-point and ISO. - - - - - - - - - - - - - - - - - - - - - - - - - - -121  
Figure 5. Block diagram of a large size intercom system using a twin  
ADAM™ configured as a 200x200 matrix. - - - - - - - - - - - - - - - - - - - - - - - - - - -123  
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CHAPTER 0  
CHAPTER 0  
CHAPTER 0  
C
HAPTER 0  
PREFACE  
Welcome to the Telex Communications, Inc. Handbook of Intercom Systems Engineering. The  
idea for this book came, as it does with many books and inventions, over drinks at a bar. A few of  
us “intercom types” were discussing our varied histories and experiences. We added up the years  
each of us had in the intercom system industry and between the four of us we hit the 75 year mark.  
Add the “rest of the gang” at Telex into that estimate and we are well past the century mark,  
quickly closing in on the two century mark. It was then we decided that we were getting old and  
had spent too much time dealing with intercoms. Someone commented that it was a shame that  
“the younger generation” didn’t really know what we seasoned pros did and suggested that we  
should pass down our profound body of knowledge for the good of “intercom-kind.”  
The idea for the book sort of hibernated for a bit after that (as did we). Weeks later we found  
ourselves planning for a trade show and discussing the appropriate “swag” for giveaways. After  
some discussion, we decided a well written, reasonably impartial, complete reference / tutorial on  
intercom system design would be a great thing – useful, desirable, business related, and maybe  
something inspirational. We hope those that read this book take advantage of the knowledge they  
can glean from it and expand the capabilities of their own intercom systems. And, maybe they  
will use some intercom equipment from Telex. In the process, we may go down in history as the  
“guys who wrote the book on intercoms.”  
The book you are starting has a number of goals; it is intended to be a systematic tutorial for the  
novice user and an encyclopedic reference for the designer in the midst of a project. It is NOT a  
®
100+ page sales brochure for Telex products. Rather, it is a resource intended to take the reader  
through the different types of intercom systems and needs, compare them, point out strengths and  
weaknesses, and provide many “real-life” examples of working systems.  
This book will be updated regularly to keep pace with changes in technology. On the enclosed CD  
you will find a good deal of technical information, systems examples, and some marketing “fluff”  
®
such as Telex product sheets, catalogs, operating manuals, etc. Throughout the book, we have  
strived to provide real examples with real products. Many of the examples will make use of  
®
®
Telex products, as that is what we know best – Telex AudioCom , RTS Matrix, RTS TW,  
®
RadioCom Wireless and Telex Headsets. If we get to a point with an example where the  
equipment needed or best suited is not one of our products, we will tell you what that product is  
and how to find it.  
I have often joked that intercoms are the “stepchild” of the industry – no one (or VERY, VERY  
FEW) people decided in high school what they wanted to do with their lives is be Mr. (or Ms.)  
Intercom. People tend to get dragged kicking and screaming into dealing with the design,  
installation and support of intercom systems because they were in the wrong place at the wrong  
time. What they later learn is that they have developed a valuable bit of niche expertise that can be  
in great demand.  
The one goal above all with this book is to provide a solid body of work, in a useful form to all  
those who have been, and will be, dealing with specification and operation, as well as, design,  
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installation and support of intercom systems. In other words, we hope this book helps you get the  
absolute most out of your communications systems.  
Apart from the story of the bar and the trade show, there is another serious reason why we have  
written this book. Intercoms (in our opinion) are a neglected, underrated, taken for granted part of  
the technical world – they are not glamorous nor interesting. I have at times made the comment  
that intercom systems have a lot in common with toilets (no off color jokes to follow). They are  
often the last system designed into an environment, they are often cheaply done, they are  
PRESUMED to be always available and always working, and when they are NOT – it QUICKLY  
becomes a crisis – and the plumber, all of a sudden is worth ANY AMOUNT OF MONEY to  
return the toilet to its normal functioning condition, FAST!  
Now, let’s take the same scenario except in the intercom world. Consider a live television show, a  
camera fails, or a microphone fails, and the audio operator can’t hear the guest, or a tape jams in a  
VTR. No problem, we’ll just TELL the TD to take another camera, and TELL Camera 2 to  
change its shot, or the audio operator will ASK the stage manager to get a spare microphone to the  
talent, or the director will TELL the talent to ad-lib until the tape can be salvaged…. “WHAT DO  
YOU MEAN, NO ONE CAN COMMUNICATE THESE SIMPLE INSTRUCTIONS!?!? Get the  
PLUMBER (oops… INTERCOM EXPERT) NOW!!!!”  
The intercom system, whether in a television station, on the sidelines of a football game, or in a  
factory is critical, and must be seamless, reliable, and work without fault to allow all needed  
communications to take place. This book is intended to help make that happen.  
We’d love to know if you think we have succeeded, or failed, or fallen short with this effort, so  
that, as with all things in life, we can learn, grow and improve. Please send your comments to  
intercoms@Telex.com.  
Ralph K. Strader  
Vice President & General Manager  
Intercom Products  
Telex Communications, Inc.  
January 2001  
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CHAPTER 0  
CHAPTER 0  
CHAPTER 0  
C
HAPTER 0  
ABOUT THE AUTHORS  
This handbook is the work of a number of past and present Telex employees, as well as, some  
outside experts (such as Stan Hubler).  
Among the contributors (in alphabetical order) are: Talal Aly-Youssef, Gene Behrend, Larry  
Benedict (contributor and editor), Rick Fisher, Stan Hubler, John King, Murray Porteous, Dave  
Richardson, Ralph Strader, and Tom Turkington. The credits for each chapter reflect the  
contribution of the primary author for that chapter. Through a group effort such as this, the words  
may actually be those of a number of individuals in any given chapter.  
Many other individuals have directly or indirectly contributed to this book, and not all of them  
can be recognized here. Many of the illustrations were prepared by John Yerxa, and many of the  
systems examples came from the work of Shawn Anderson, Chuck Roberts, Gene Behrend, and  
Geoff Rogers.  
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C H A P T E R  
1
C
HAPTER 1  
INTERCOMS—AN OVERVIEW  
RALPH STRADER  
Introduction  
Intercom systems, by definition, may be comprised of many different types of intercoms  
and subsystems. The basic building blocks can be categorized into four basic types or  
elements: Party-Line Systems, Matrix Systems, Wireless Systems, and Accessories.  
Party-Line Systems  
Wired Party-Line systems are systems in which a number of participants are all involved  
in the same conversation. Think of the telephone extensions in your home, if each person  
in your family picks up a telephone in your home, you will all be able to hear each other.  
You can talk to one another simultaneously and the person “on the other end of the line”  
will be a full participant in one “public” conversation.  
Depending on where in the world you are from, (presuming English language), you may  
also refer to this type of system as “PL” (for “party-line), “TW” or “Two-Wire” from the  
telephone systems, where on two wires, a full duplex conversation takes place, or  
“conference” denoting the type of activity taking place in the conversation.  
Figure 1.1 Simple Party-Line System  
Note, the physical configuration and implementation of that “PL” or “TW” does not  
necessarily need to be on two physical wires, in most cases it is not. The specific  
topologies will be addressed in the chapters that follow.  
C h a p t e r 1 - I n t e r c o m s — A n O v e r v i e w  
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Matrix Systems  
Wired Matrix systems are systems in which a large number of individuals have the ability  
to establish private individual conversations from point A to point B. Again, going back to  
the telephone system in your neighborhood, you, your next door neighbor, the pizza joint  
down the street and the local gas station are all connected to the same central office by  
wires from each location back to the telephone company. At any time, you can be talking  
to the gas station, while your neighbor is ordering a pizza. The pizza guy does not hear you  
ask the mechanic about the repairs on your SUV.  
Depending on where in the English speaking world you are, you may refer to these types  
of systems as Matrix systems, crosspoint intercoms, point-to-point systems, private lines  
(sometimes, confusingly referred to as “PL”), or by some of the brand names used:  
McCurdy, ADAM , Zeus , and others.  
Figure 1.2 Simple Matrix System  
MATRIX  
You  
Neighbor  
X
X
Pizza Joint  
Gas Station  
X
X
You  
Neighbor  
Gas  
Station  
Pizza  
Joint  
Like the telephone system, matrix systems have other functions and capabilities.  
Conferences, call waiting, busy signals, and other features are common to many matrix  
intercoms. They are not limited to simple point-to-point communications. Some systems  
even allow inter-matrix routing of signals, similar to long distance telephones calls using  
trunks between central offices. Having a matrix system with a number of conferences  
configured within it (virtual PLs) is very common.  
Wireless Systems  
Wireless Intercoms encompass all sorts of systems from the most basic pair of “walkie  
talkies” to cell phones to dedicated professional full duplex intercom products. The most  
basic feature of wireless intercoms is that they are not tethered by wires. (Didn’t think this  
was going to be quite that basic, did you?) Seriously, wireless intercom systems are  
employed where the limitation of wireless systems which can include fidelity,  
interference, lack of range, lack of security (real or perceived), and battery life limitations  
are outweighed by the freedom of being cordless. This freedom can be essential in many  
applications—try dragging a wired intercom cable into the containment vessel of a nuclear  
reactor.  
Wireless intercom systems can be designed, installed, configured and operated in PL or  
matrix configurations, and may very likely be connected to a hard-wired PL or matrix  
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intercom system at some point. They can range from as simple as a single pair of units  
talking to one another, to a system in which 24 or more different portable units are  
dynamically switched between conversations.  
Figure 1.3 Wireless Intercom Examples  
Transmit to  
Beltpacks  
BTR-300  
BTR-300  
RadioCom  
Portable Transmit On  
1
2
3
4
Ext Intercom Aux Audio  
Headset Controls  
Portable Station Connect  
Talk  
Gain  
O/M  
Power  
Push Twice to Latch  
Headset  
Volume  
Transmit to  
Base  
TR-300  
TR-300  
TR-300  
TR-300  
Mirror Image Pair  
Telex TR-500  
Base Station with  
4 Remotes  
Wireless systems will vary tremendously worldwide, due to varying governmental radio  
regulations. What is common in America may be illegal in Japan, and may be unsuitable,  
for other reasons, in Germany. These units may be referred to by any of the types  
mentioned above, but, again, the unifying feature is the freedom from a wire.  
Accessories  
The fourth and final category is “accessories”. We are giving accessories its own separate  
category because of its importance. This book is addressing intercom systems. In all  
likelihood, many of the systems you encounter will be an amalgam of the three types  
mentioned above. Without “accessories” you cannot have a system, just a bunch of  
equipment.  
To connect a TW system to a matrix system, a converter is required to change the  
combined talk and listen signal from the TW to separate talk and listen signals for the  
matrix – a hybrid provides this conversion.  
C h a p t e r 1 - I n t e r c o m s — A n O v e r v i e w  
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Figure 1.4 Example of Interfacing a TW System to a Matrix System  
To connect a matrix intercom system to a Two-way radio system, a contact closure may be  
required to activate the radio transmitter. A GPI (General Purpose Interface) between the  
matrix and the base station of the radio can solve this problem easily.  
To do intelligent trunking between matrix systems, across campus or across the country,  
the audio and control signals between the matrices could be transported over fixed pairs of  
wires. Realistically, however, installing a set of wires between Omaha and Los Angeles  
may be out of your budget – so an interface allowing the use of dial-up telephone lines  
may be needed. Other possibilities include muxes and demuxes to allow the audio and data  
to be carried over an existing corporate Wide Area Network (WAN), or “piggybacked” as  
subcarriers on an existing satellite feed.  
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Figure 1.5 Complex Matrix Intercom System  
MATRIX  
Audio IN,  
Audio OUT,  
Data  
Third Party  
PL  
2
UTO  
N1UM  
SUST  
A3  
IFB  
ISO  
LISTEN  
NEWS  
PHONE  
4
DIR  
PROD RA  
PL01 IFB4  
TD  
AD  
T1 TEL1 TEL2 FLOR CHYR ISO1 ISO2 AUD1  
5
6
RELA  
Y
E-PANL  
8
C7OPY  
9
DISPLA  
Y
Terminal  
CLEAR  
CALL  
MUL  
CLR  
0T  
PGM  
FUNC  
Equipment  
Analog  
Audio  
Keypanel  
LAN / WAN  
Third Party  
Terminal  
Equipment  
Audio IN,  
Audio OUT,  
Data  
Email  
System  
News  
Computers  
PL  
2
UTO  
N1UM  
SUST  
A3  
Third Party  
Terminal  
IFB  
ISO  
LISTEN  
NEWS  
PHONE  
4
DIR  
PROD RA  
PL01 IFB4  
TD  
AD  
T1 TEL1 TEL2 FLOR CHYR ISO1 ISO2 AUD1  
5
6
RELA  
Y
E-PANL  
8
C7OPY  
9
DISPLA  
Y
CLEAR  
CALL  
MUL  
CLR  
0T  
PGM  
FUNC  
Equipment  
Keypanel  
In many cases, connection to “the telephone company” is required to allow a reporter to  
connect into an intercom from his or her cell phone, or to allow a return program feed to be  
fed to a remote location. A telephone interface (TIF) unit provides this connectivity.  
The most basic accessory in an Intercom system may be the headset. It may provide  
isolation from ambient noise; it may have a noise-canceling microphone to reduce wind  
noise, and may have stereo ear pieces to allow program audio and intercom audio to be fed  
independently to the right and left ears.  
Each of these accessories is vital to creating an intercom system that meets the  
communications needs of the users.  
Before We Begin  
Throughout this book, you will be subjected to the jargon that permeates the intercom  
world. In the chapters that follow, you will be presented with definitions specific to the  
topic being covered. In many cases, there are common terms that will be applicable to all  
these chapters, and so we will present a few definitions to get us started. We have also  
provided a comprehensive glossary in the rear of the book.  
IFB  
Interrupted Fold Back – also referred to as IRF – Interrupted Return Feed. The best way to  
explain this is to give an example. A news reporter is on the scene of live accident  
coverage. She needs to not only hear what the anchor back at the studio is saying i.e., “So,  
Jane, how many chickens were injured when they tried to cross the road during rush  
hour?” She also needs to hear instructions from the director back in the studio i.e., “Wrap  
it up, 10 seconds.” The IFB function in an intercom system allows a single audio signal to  
be sent to Jane, normally containing program audio interrupted by instructions or  
information from someone not a part of the program audio.  
C h a p t e r 1 - I n t e r c o m s — A n O v e r v i e w  
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ISO  
Camera Isolate – This is not reserved strictly for the domain of cameras anymore. This is  
truly an isolate function, not unlike the action at a party of grabbing the arm of a fellow  
guest, dragging them off to a corner for a private conversation, and then returning them to  
their group. There are instances where it is necessary in an intercom system to establish a  
momentary private conversation with someone who may be talking and listening to a  
number of other people. The person who needs to interrupt presses a button or key, which  
establishes a private two person conversation. Upon releasing the key, the two participants  
are returned to whatever conversation(s) they were a part of previously. This was called  
Camera Isolate as it first was used to remove an individual camera from a conference to  
allow private communications.  
Tally  
A signal sent for the purpose of indicating status for a particular purpose. The sound of  
your telephone ringing can be described as a tally. On an intercom panel with multiple  
channels, it can be a visual signal, such as a blinking light, to indicate which station is  
calling. It can be used to indicate a particular function is not available due to a conflict –  
similar to the busy signal you get when calling the radio station trying to be the tenth caller  
and win a year’s supply of cat litter.  
The above definitions and many more can be found in the glossary at the back of this  
book.  
The Rest Of The Book  
We have organized this book by the above types of systems – two chapters devoted to PL  
Intercoms, two chapters for matrix systems, two chapters for wireless systems, and one  
chapter on interfaces, determining systems needs and requirements, technical  
requirements for installation, and some real world case studies.  
Near the end of the book, we have included references for further information, a glossary,  
®
and a CD full of information on Telex Products, technical references, and many system  
drawings.  
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C H A P T E R  
2
C
HAPTER 2  
INTRODUCTION TO PARTY-LINE  
INTERCOM SYSTEMS  
STAN HUBLER  
Introduction  
Leading off this chapter, Some Definitions that may help you understand Party-Line  
intercoms terms (and buzz-words). Then, a Short History of Party-Line intercoms will be  
presented, leading into a discussion of Present Day Systems and Manufacturers. The  
System Components and Their Function will explore the main components of these  
systems and what they do. Then, How Each System Works shows how these system  
components are put together to make a functioning intercom and some examples of the  
different systems. Outstanding Features of Each System describes application areas and  
where each system is often marketed. Some important Limitations of Each System are  
described and a Summary closes this chapter.  
Some Definitions  
Party-Line (PL) systems / Conference Line Intercom Systems  
A Party-Line system allows a group of people to intercommunicate. For example, one  
person can talk, while all the others on the bus or channel can hear. When the system is full  
duplex, anyone can talk and the rest can hear or interrupt the speaker at any time. The  
Party-Line and distributed matrix systems presently sold today are usually full duplex and  
are non-blocking, which means that access to the channel is immediate and there is no  
busy signal. Conversations on Party-Line systems are, in general, non-private. It is  
important to note that both two wire and four wire type systems support the Party-Line  
concept.  
Two-Wire  
A communications system where the path is the same for both talk and listen. In electrical  
pathways there are, in fact, two wires (one path). Two-wire systems can be two-wire  
balanced or two-wire unbalanced.  
C h a p t e r 2 - I n t r o d u c t i o n t o P a r t y - L i n e I n t e r c o m S y s t e m s  
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Balanced Line  
The balanced line concept reduces noise pickup by outside sources. A balanced two  
conductor line carries audio that is differentially driven and balanced to ground.  
Full Duplex  
This is communication that allows simultaneous two-way conversations, that is, one  
person can interrupt the other. In data communications, full duplex permits confirmation  
of sent data by the receiving terminal echoing, sending back the same data, or confirming  
data.  
Decibel (dB)  
A derived unit of loudness. The human ear perceives a 10 decibel increase as twice as  
loud, and a 10 decibel decrease as half as loud.  
Beltpack  
A portable headset user station. This station is designed to be worn on a user’s belt, but is  
also fastened to the underside of consoles, taped to a structure near the user, or mounted on  
a piece of equipment. The headset plugs into the user station, as does the connection to the  
rest of the intercom.  
Biscuit  
Marketing buzz word for a portable speaker station.  
Main Station  
A multichannel user station. There may be one or more of these stations in a system.  
Usually the primary station in a system.  
Master Station  
A user station where a user station and a system power supply are combined into one  
package  
Sidetone  
In the truest sense, sidetone is a small amount of microphone signal fed back to the  
earphone of the individual speaking into the microphone. In a two type user station, the  
null balance control is sometimes used to adjust the amount of sidetone the user hears.  
This control is sometimes (erroneously) called the sidetone control. Other equipment has  
both null balance adjustments and a true sidetone adjustment.  
Crosstalk  
Unwanted interference caused by audio energy from one line coupling (“leaking”) into  
adjacent or nearby lines.  
A Short History  
Party-Line intercoms were needed early on by television production crews to coordinate  
their activities. Some of the activities included on-site sport pickups, entertainment on  
stage, and videotaping of shows. The crews included camera operators, audio, lighting,  
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stage directors, director, assistant director, production assistant, and others. Originally,  
these crews shared one intercom channel where the director called the shots. Later, as  
intercom developed, additional channels were added so each crew could still listen to the  
director, then could switch to their own channels to coordinate activities without conflict  
with the director. Party-Line intercom systems were also used by industrial activities to  
coordinate manufacturing and testing of large systems such as aircraft.  
Early intercom systems (1960-1975) were either homemade or accumulations of telephone  
equipment lashed together. Often, the homemade intercoms worked well enough but  
lacked the flexibility to expand the system or interface with other systems. The telephone  
equipment approach had some flexibility, but performance degraded rapidly as the number  
of stations increased above ten user stations.  
In the early 1970s, Clear-Com built Party-Line systems for rock-n-roll concerts, and later  
for theatrical stage, and eventually for television production. This system was flexible and  
expandable, but required one three-conductor microphone cable for each channel. In the  
mid 1970s, another company, RTS Systems, designed a system for television production  
that had two channels on one three-conductor microphone cable (or one channel on a pair  
of wires). This system was even more flexible and expandable with a design that allowed  
up to 50 user stations on a single channel. On the East Coast, a company, Chaos, produced  
intercoms for the New York and other stages. And, in the Midwest, a company, Telex  
Communications, produced a balanced Party-Line system. This system was especially  
useful in noisy electrical environments, because it was immune to induced interference.  
Other Party-Line systems include systems such as David Clark, which is used for fire  
trucks and similar public safety and service crews. And, of course, four wire matrix  
systems can emulate Party-Line intercoms.  
®
As Clear-Com and RTS Systems intercoms became more widely known, compatible  
systems of both appeared. They included HME and Production Intercoms for Clear-Com,  
and ROH and Anchor Audio’s PortaCom for RTS . Chaos is similar to Clear-Com,  
except it uses a much higher power supply voltage (46 vs. 24 volts). As the markets  
expanded, the distinction between theatrical and television production became blurred and  
Party-Line systems of all types were used wherever they were needed. So a competitive  
atmosphere developed and continues to the present. ROH and HME are no longer in the  
wired intercom market.  
Present Day Systems and Manufacturers  
The three major brands of “two-wire” Party-Line intercoms having the largest worldwide  
presence are RTS, Clear-Com, and Telex Audiocom. Other brands include Chaos, David  
Clark, PortaCom, and Production Intercom.  
Table 2.1 Intercom brand name vs. manufacturer.  
Brand Name  
Manufacturer  
Audiocom®  
Telex Communications, Inc.  
Goddard Design Company  
Clear-Com Intercom Systems  
David Clark Company, Inc.  
Anchor Audio, Inc.  
Chaos  
Clear-Com  
David Clark  
PortaCom  
Production Intercom  
RTS™  
Production Intercom, Inc.  
Telex Communications, Inc.  
Note Present day Party-Line intercom systems are mostly distributed amplifier type systems as  
opposed to a centralized system where all the headset lines plug into one box (Some David  
Clark Systems are of a centralized type). Oh yes, there is a no-amplifier system called a  
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sound powered system, but we do not discuss it here. Present day Party-Line intercom  
systems may be wired or wireless or both.  
System Components and Their Function  
The system components for most Party-Line intercoms consist of power supplies (or  
master stations), user stations (e.g. belt packs, speaker stations, main stations, etc.),  
interconnecting cable, headsets, panel microphones, push-to-talk microphones, and a  
system termination.  
The power supply (which is normally centralized) generates the DC power for the entire  
system (with the exception of self powered user stations). The power supply usually  
includes system termination for the audio channel, 200 ohms for RTS and Clear-Com, and  
300 ohms for Audiocom. This may be as simple as a capacitor and resistor in a series, or,  
an electronic termination, which is integrated into the power supply voltage regulator.  
The user station connects to the power supply and intercom line. The human user connects  
to the user station via a headset or loudspeaker and microphone or some combination. For  
a given channel or channels the user stations are connected to each other in parallel.  
The interconnecting cable for most intercoms is standard microphone cable with three pin  
XLR type connectors. The female XLR connects towards the power supply and the male  
XLR plugs into the user station. This polarity was chosen to prevent putting DC power  
onto audio microphones which also use this type cable. There are at least two exceptions to  
the use of microphone cable: the RTS TW master stations connect audio with  
unshielded pairs (12 of the 25 pair in a cable). Another exception is where a twisted pair is  
the only connection between two points. The RTS TW user stations can connect directly  
to a twisted pair, while other user stations need adapters of one kind or another, and power  
may have to be supplied at either end.  
The wired systems are of three wiring configurations: 1) separate power, audio, and return  
conductors (example: Clear-Com), 2)an audio pair which includes phantom power and a  
common (example: Audiocom), and 3) a conductor that contains one channel and power, a  
conductor that contains audio with- or without power, and a return (example: RTS  
TWTW intercom system).  
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Table 2.2 Intercom connector wiring by various manufacturers.  
Clear-Com  
Pin #  
Function  
1
Common for Audio, Power, &  
Shield  
2
3
DC power: 30 volts nominal  
Unbalanced Audio  
Audiocom  
Pin #  
Function  
1
Common for Audio, Power, &  
Shield  
2
3
Audio + DC Power  
Audio + DC Power  
RTS TW  
Pin #  
Function  
1
Common for Audio, Power &  
Shield  
2
3
Channel 1 Audio + DC Power  
Channel 2 Audio  
The wireless systems usually include an interface to the wired systems. Principal  
manufacturers include Telex Communications, Vega (now part of Clear-Com), and HME.  
We will go into further detail on wireless systems in a later chapter of this manual.  
Wired intercoms are mostly of the distributed amplifier kind. The distributed amplifier is  
built into a User Station. User stations come in various packages and are of three kinds:  
headset, speaker-microphone, or both. The various packages include a belt pack (worn on  
the users belt, and of the headset kind), console mount (headset or speaker-microphone),  
rack mount (headset or speaker-microphone), desk mount (portable speaker station), wall  
mount (headset or speaker-microphone), and console/rack mount Master Station/Main  
Station (details later). The distributed amplifier concept allows each user to adjust his/hers  
own listening level. The user station also includes a microphone amplifier, a line  
amplifier/buffer, volume control(s), talk switch(es). Some user stations also may have a  
Call light, status indicators, and a channel selector. The microphone may be in the headset,  
fastened to or plugged into a speaker station, in a handset, or in a push-to-talk hand held  
unit.  
Belt Pack Headset User Station Functional Description  
A typical single channel belt pack headset user station has the following connectors:  
Intercom Line (XLR-3) and a Headset Connector (XLR-4).  
The station has the following controls:  
Microphone ON/OFF (sometimes called a TALK switch), and a headset Volume Control.  
It may also have a Call Lamp and a Call Lamp Send button. Examples of this station are an  
®
®
RTS BP318 single channel belt pack, or an Audiocom BP1002, or a Clear-Com RS-  
501.  
A typical two channel headset belt pack user station adds a channel selector switch to the  
®
®
above. Examples RTS BP351, Clear-Com RS-502, Audiocom BP2002  
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Alternately, newer units have two talk buttons, two volume controls, and two status  
indicators to tell which talk button is engaged. Examples: RTS BP325, BP351, Clear-  
®
®
Com RS-522-TW, or Audiocom IC-2B.  
Speaker User Station Functional Description  
A typical speaker station can function with either a headset or a speaker/microphone. A  
power amplifier, a speaker, and a speaker on/off switch are added to the electronics of a  
belt pack. In addition, a nulling adjustment is easily accessible. The nulling adjustment  
allows for full duplex operation without unwanted feedback. Also added is a connection or  
jack for either a panel microphone (rack mount stations) or a push to talk microphone (for  
desk mount or portable speaker stations).  
Master Stations  
The Master Station allows a user to access multiple channels. This allows different crews  
to be monitored, cued or updated. If the master station is used for training, again, different  
crews may be monitored and guided. These master stations have extra features for special  
tasks such as IFB (Interrupted FeedBack) or SA (Stage Announce), relay closures, “hot”  
microphones, and microphone kill. Master stations can send and receive call light signals  
®
on any channel. Two examples of the Master station are Clear-Com Model 912 (12  
channel) and RTS Model 803 (12 channel). Audiocom’s master station is modular and  
can be as few as 2 channels or as many as 22 channels. Master stations allow simultaneous  
monitoring of any channel, any combination of channels, or all the channels. They can call  
or “mic kill” on any given channel. In addition, some master stations can monitor a  
program source.  
Some Technical Notes About The Stations Above  
The stations mentioned above generally are designed for the dynamic microphones in the  
headsets to have an impedance of about 150 to 500 ohms. The speaker station panel  
electret microphones are designed to have an impedance of 1000 to 2000 ohms and require  
1 to 5 volts excitation. And, the push-to-talk microphones have around 500 ohms. This  
means the actual input impedance of the station microphone preamplifier will range from  
470 ohms to 5000 ohms. The low impedance of 470 ohms minimizes the crosstalk in the  
headset cord. The headphone impedances expected range from 50 ohms to 1000 ohms.  
The 50 ohm headphones along with suitable headphone amplifiers provide enough SPL  
(Sound Pressure Level) to overcome the interference from loud concerts and sports events.  
The headphones also need to have an acoustic isolation of 20dB or more to protect the  
user. These stations generally have a bridging impedance across the intercom line of  
10,000 to 15,000 ohms. A bridging impedance of 10,000 ohms assures that up to 50  
stations can be plugged into the systems and the level drop will only be 6dB. The level  
drop of 6dB corresponds to the level drop when an extension telephone is picked up on an  
existing conversation-noticeable but the telephone is still usable.  
®
®
Wiring Notes 1 Clear-Com and Audiocom two channel stations have 6 pin XLR connectors to  
®
connect to the intercom line. Clear-Com also offers the Clear-Com RS-522-TW,  
which has two channels on a 3 pin XLR.  
®
®
2 Clear-Com and Audiocom systems use a female 4 or 5 pin XLR connector on their  
headsets and a male 4 or 5 pin XLR connector on their user stations. However, RTS  
uses a male 4 or 5 pin XLR connector on their headsets and a female 4 or 5 pin XLR  
connector on their user stations.  
3 In any system, pin 1 and the shell of the XLR connector should NOT be connected  
together.  
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4 The pin out of the headset connectors is as follows:  
Four pin XLR  
Pin 1 - Microphone common  
Pin 2 - Microphone “hot”  
Pin 3 - Headphone common  
Pin 4 - Headphone “hot”  
Five pin XLR  
Pin 1 - Microphone common  
Pin 2 - Microphone “hot”  
Pin 3 - Headphone common  
Pin 4 - Left Headphone “hot”  
Pin 5 - Right Headphone “hot”  
5 Since the power supply has a limited amount of XLR-3 connectors, splitter boxes are  
used to expand the system. These boxes have all the connectors wired in parallel.  
6 Some user stations have “loop-thru” connectors that allow “daisy chaining” stations  
using a single connection to the power supply.  
How Each System Works  
Note Drawings at the end of the chapter depict the systems being discussed.  
First, please note that although these systems are full duplex and everybody could  
theoretically talk at once, this is not at all practical or desirable. The usual operation is the  
director or lead person has their microphone enabled all the time, while all other  
microphones are switched off. These microphones are switched on only long enough to  
supply an answer, make a request, or give data. In some cases, especially in noisy  
environments, all microphones are off and only switched on as required. Because the  
Party-Line concept has so many signal sources, this operational protocol is the only way  
the Party-Line can be effective. And this is the reason for the system “mic kill”  
(microphone turn-off) capability, for the situation where a station is unmanned but has its  
microphone enabled.  
These systems use voltage controlled current sources (or similar electronics) to apply a  
signal to the intercom line. All the signals applied are summed and converted to a voltage  
at the single termination resistor or electronic impedance. The current sources (or similar  
circuits) have output impedances of 10,000 ohms or greater. The loading effect of the  
station on the intercom, say in a 200 ohm terminated system is, worst case, 10,000 ohms in  
parallel with 200 ohms. This results in a change of the system termination to 196 ohms, a 2  
percent change. This, in turn, causes a voltage change of 2 percent or 0.175dB, an  
imperceptible change. It takes 20 stations across the line to cause a 3dB change, a  
perceptible but not significant change. The volume controls in the user stations easily  
adjust for this change. In the “not so” worst-case situation, these systems can work with up  
to 75 stations, provided enough DC power is available. The work-around in this case, in  
the RTS TW system, is a switch on the power supply which doubles the system  
impedance. Then, two power supplies can divide the DC load and are coupled together  
with capacitors to end up with the 200 ohm termination and twice the user stations. In the  
case of Clear-Com, the system termination is not electronic but a passive resistor. If an  
®
adapter is made, the same trick can be done in a Clear-Com system power supply. In the  
case of Audiocom® intercoms, paralleling two power supplies with capacitors would  
result in an impedance of 150 ohms which could still be usable in some instances.  
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System Powering  
Systems can be centrally powered with a power supply or they may be individually  
powered with “local power” modules, also known as built-in power supplies. The systems  
®
can also be a mixture of central and local power. In the cases of Audiocom systems and  
RTS TW systems, the power and signal share the same wire(s). This means, for those  
two systems, the power supplies DC source must be ultra low noise/quiet, circa -70dBu or  
better. Most systems can work using main powers of 120 or 240 volts AC. Some  
individual stations can be powered with 2 or 3 nine volt batteries in series. Venues such as  
the Rose Parade may have to use a pair of batteries from the telephone company just to  
cross the street. Since this may involve a mile of copper wire, there is no central DC source  
that’s going to make it. Out come the nine volt batteries! The RTS TW power supplies  
can tolerate only a 5 volt peak-to-peak signal on the powered line. In this system, each  
station can generate a maximum 2 volt peak to peak signal, so two stations talking  
simultaneously can add up to 4 volts peak to peak. So, there is just 1 volt of headroom.  
Clear-Com specifies a range of signal levels of .5 v p-p to a maximum of 4v p-p, but  
®
doesn’t specify the reference (it is probably dBu or dBv). Audiocom intercoms specify  
only a nominal level of 1 volt RMS, which is equivalent to 3 v p-p.  
Headset User Stations  
The microphone preamplifier has a maximum gain in the neighborhood of 53 dB. Many  
stations have Automatic Gain Control (AGC), which adjusts the gain according to the  
incoming microphone signal. Some stations also have a limiter that prevents overloading  
the intercom line. An electronic switch is placed between the microphone preamplifier and  
the current source (line driver). This substantially reduces noise on the intercom line. A  
hybrid connection is necessary to sort out the talk and listen signals (a two wire to four  
wire converter would work best). The listen signal goes from the hybrid to the listen  
volume control. The listen volume control drives the headphone amplifier that has a gain  
in the range of 30 to 40 dB. For a 50 ohm headset, the headphone amplifier produces  
maximum peak sound pressure levels of around 105dB. This is the level needed at  
concerts and sporting events (along with 20dB acoustic isolation of the headset). In less  
strenuous situations, a handset instead of a headset may be used with these stations. These  
stations must have a bridging impedance of 10,000 ohms or higher. The current drains  
range from 30 to 65 milliamperes. Most systems have signal levels that range from -15dBu  
®
to 0dBu. In the case of Clear-Com and RTS TW systems, the AGC / limiters in the  
microphone preamplifier tend to keep the level in the -10dB range. This enhances  
intelligibility and compensates for differences between voices and headset microphones.  
Usually the headset amplifier has enough gain to make up the differences (by readjusting  
the volume control).  
Speaker User Stations  
Most of these stations can operate in both a speaker/microphone mode and a headset  
mode. The difference between a headset only station and the speaker station is that a  
speaker amplifier, switching electronics, and a null pot are added. Usually the portable  
speaker stations use a push-to-talk microphone, whereas the fixed speaker stations use a  
panel or gooseneck microphone. The stations that have microphone and speaker on the  
same panel have less available speaker level because of feedback. The push-to-talk  
microphone has much better isolation. Speaker stations often have “dimming” or  
“ducking” which attenuate the speaker output when the microphone is keyed. This allows  
more gain and less feedback. Speaker stations use a very substantial amount of current,  
about 120 milliamperes. So, fixed speaker stations are ideally operated with local power,  
to prevent overloading the central power supply. Some RTS TW are direct AC powered  
and do not use central power.  
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Master Stations  
These are multichannel stations. Some Master Stations are balanced (RTS TW Model  
802/803) and require an interface (RTS TW Model 862 or 4012) to work with  
unbalanced channels. Master Stations can be configured to work with their respective  
systems with a minimum of interfacing. Master Stations have many functions which we go  
into to detail later.  
Cabling  
Usually the intercom system’s specifications are based on the use of 22 AWG microphone  
cable. Microphone cable of 22 gage measures 3 ohms per 100 feet or about 30 ohms per  
1000 feet (round trip resistance). The wire table says 32 ohms per 1000 feet round trip, but  
®
the shield resistance is much lower than the wire resistance. The Audiocom system uses  
both wires and the shield to transport DC so the calculations will be different for DC  
voltage drop versus distance.  
Outstanding Features of Each System  
®
The Audiocom system is immune to noise and is a lower cost system. It is used in  
difficult environments, i.e.: churches, concerts, theaters, and sporting events.  
®
The Clear-Com system is robust, relatively lower in cost, and rental systems are readily  
available. It is often used for concerts, rock-n-roll tours, and in theaters. It is also used in  
remote trucks, uplink trucks, and low budget venues.  
The RTS system is also very robust, reasonable in cost, and rental systems are readily  
available in most countries world wide. Because the RTS intercom has two channels per  
microphone cable, it is used where many channels are required, such as the Oscar and  
Emmy award shows. It is also used for events such as the Superbowl. Most larger TV  
trucks carry both a four-wire system and an RTS Party-Line system. These systems are  
interfaced together so the four-wire is used inside the truck and the RTS system is used  
outside the truck.  
In addition to these features, most systems support extra features such as, “microphone  
kill” and “call light”. The microphone kill feature allows all microphones in a given  
channel to be switched off. In the case of Audiocom and RTS, the signal is an inaudible 24  
kilohertz. In the case of Clear-Com, the power is interrupted for a long enough time to  
reset the microphones to off.  
Call Lights  
The Call Light Signal allows user stations to generate and display a visual signal for  
attention-getting and cueing purposes. The flashing light of the RTS and Audiocom  
®
®
systems alerts the crew to put their headsets back on. The steady light of the Clear-Com  
system can also be used for this purpose, however, it has another purpose: when the  
director holds the call light on, this is a standby signal. When the light goes off, this is the  
execute signal (raise/lower the scenery, follow spot on, et cetera). Call signals can also be  
®
used to key 2-way radios, sound alarms, and activate lighting controls. Audiocom and  
®
RTS systems use an inaudible 20 kilohertz signal for the call signal; Clear-Com  
systems use a DC voltage added to the audio signal. Telex manufactures a call signal  
detector / display (Model CIA-1000) which provides both a high visibility light and a relay  
®
closure when a call signal is sent. The CIA-1000 works with RTS TW and Audiocom  
systems. Clear-Com and other manufacturers also provide similar products. The company  
VMA supplies a bright strobe lamp that is triggered by the RTS system call signal. This  
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strobe is powered from the RTS line but only draws 10 milliamperes. It also supplies a  
relay closure and a logic signal.  
Limitations of Each System  
Cable capacitance, resistance, and crosstalk affect all three systems. The longer cables  
(over 2000 feet) limit the number of belt packs at the end. A system with cumulative  
cables adding up to 10,000 feet will have a reduction in frequency response due to cable  
capacitance. Both resistance and capacitance affect crosstalk.  
®
If all you have is a twisted-pair cable, then the RTS system is most useful. If you have  
severe coupling with power cables, the Audiocom system will help.  
Some of the information in this chapter is repeated in the next chapter, but in a different  
context.  
Summary  
(Some Definitions)  
1
2
A Party-Line system allows a group of people to intercommunicate.  
“Two-wire” means a communications system where the path is the same for talk and  
listen.  
3
4
5
6
7
8
9
A balanced line reduces unwanted noise and crosstalk pickup.  
A full duplex intercom allows simultaneous two-way conversations.  
The human ear perceives a 10 decibel increase as twice as loud.  
A belt pack is a user station designed to be worn on a user’s belt.  
A main station is a multichannel user station.  
A master station combines a user station and a power supply.  
Sidetone is a small amount of microphone signal fed back to the user’s ear.  
10 Crosstalk is unwanted interference.  
(A Short History)  
1
2
3
Television, theatrical, and concert production crews need Party-Line intercoms.  
Party-Line intercoms are also used for training and for industrial crews.  
Early intercoms were inflexible and limited to small groups of users and sometimes  
short distances.  
In the 1970s, fresh new designs were the beginning of the modern Party-Line  
intercoms we use today.  
(Present Day Systems and Manufacturers)  
1
Principal “two-wire” Party-Line brand names today are Audiocom, Clear-Com, and  
RTS. Other brand names are Chaos, David Clark, PortaCom, and Production  
Intercom.  
2
With the exception of David Clark, present day Party-Line intercoms are the  
distributed amplifier type.  
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3
This format allows louder and clearer communication. Party-Line intercoms can be  
wired or wireless or both.  
(System Components and Their Function)  
1
The system components for most Party-Line intercoms consist of power supplies (or  
main stations), user stations, interconnecting cable, headsets, panel microphones,  
push-to-talk microphones, and a system termination.  
2
The power supply (normally centralized) generates DC power for the entire system  
(exception: self powered user stations).  
3
4
5
6
7
8
9
The power supply usually includes the system termination.  
User stations connect to the power supply and intercom line(s).  
For a given channel, user stations are connected in parallel.  
The interconnecting cable for most intercoms is standard microphone cable.  
For the major three intercoms (and their clones) there are three wiring schemes.  
Wireless intercoms usually include and interface to the wired systems.  
Wired intercoms are mostly of the distributed amplifier kind.  
10 Distributing the amplifiers allows for better performance and more features.  
11 A single channel belt pack has an intercom line connector, a headset connector,  
volume control, and a talk or microphone on/off switch. A two-channel belt pack  
adds a channel selector or two talk switches and two volume controls.  
12 A speaker station usually can be a headset or a speaker station.  
13 Speaker stations add a power amplifier, speaker, and speaker on/off switching to the  
headset station electronics.  
14 Master Stations are multichannel and allow a director or lead person to have separate  
conversations with various crews in any combination. Master Stations often have  
many additional functions.  
15 Dynamic microphones used with intercom stations usually range from 150 ohms to  
500 ohms impedance. Electret microphones range from 1000 to 2000 ohms  
impedance and require 1 to 5 volts DC excitation voltage.  
16 Headphones range in impedance from 50 to 1000 ohms. For concerts and athletic  
contests, 50 ohm headsets work better. The headphones should also have at least  
20dB acoustic isolation for concerts and athletic contests.  
17 The bridging impedance of each station should be 10,000 ohms or greater.  
18 Since the power supply has a limited number of connectors, splitter boxes are needed  
to expand the number of user stations in a system.  
19 Both male and female XLR-4 connectors are used to connect the headset with the  
user station. XLR-5 connectors are used for binaural headsets.  
20 Some stations have loop through connectors to allow daisy chaining of stations.  
(How Each System Works)  
1
The stations use a voltage controller current source or similar electronics to apply  
signal to the intercom line, yet exhibit a bridging impedance of 10,000 ohms or  
greater.  
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2
3
4
Systems can be powered from a central power supply or local powered modules.  
Using local power modules allows more stations to be on the system.  
If a station is too far away to get enough DC power, batteries can be used as a work-  
around.  
Headset User Stations have a microphone preamplifier with a maximum gain around  
53dB. Many stations have an AGC (Automatic Gain Control) that adjust the gain to  
the incoming microphone signal level. Some stations also have a limiter to prevent  
overload to the intercom line.  
5
Headset User Stations have a hybrid function to convert the two-wire signal to a four-  
wire signal. The listen part of that signal is sent to the volume control and then to the  
headphone amplifier.  
6
7
Portable Speaker User Stations usually have a push-to-talk microphone that gives  
good speaker to microphone isolation. Fixed stations have a panel microphone.  
The cabling used in these intercom systems is usually called out as 22 AWG. Use of  
a smaller diameter wire such as 24 AWG shortens maximum distances and the  
number of user stations on a cable.  
(Outstanding Features of Each System)  
®
1
The Audiocom system is immune to noise and is a lower cost system. It is used in  
difficult environments, i.e.: churches, concerts, theaters, and athletic contests.  
®
2
The Clear-Com system is robust, relatively low cost, available as a rental. It is  
often used for rock and roll tours, other concerts, in theaters, and in smaller outside  
broadcast trucks.  
3
The RTS TW system is very robust, reasonable in cost, rental systems are available  
almost worldwide. Used every place, but especially where many multiple channels  
are needed such as the Oscar ceremony.  
4
5
Most larger TV trucks carry both a four-wire system and an interfaced RTS TW  
system.  
Call Lights and “mic kill” features are in all three major brands. The Call Light  
signal can be used to operate relays, radio keying, and warning lamps.  
(Limitations of Each System)  
®
®
1
2
3
Audiocom and Clear-Com systems require three wires for a single channel.  
The RTS TW system may have crosstalk (but this is rarely a complaint).  
All systems that use microphone cable are subject to distance limitations, as well as  
the number of stations per cable.  
®
4
Clear-Com systems and RTS TW system have less immunity to outside  
interference (practically speaking, rarely a problem).  
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Figure 2.1 Audiocom® intercom concept.  
Figure 2.2 Clear-Com® intercom concept.  
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Figure 2.3 RTS TW intercom concept.  
Figure 2.4 RTS TW user station block diagram.  
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C H A P T E R  
3
C
HAPTER 3  
DESIGN OF PARTY-LINE  
INTERCOM SYSTEMS  
STAN HUBLER  
Overview  
In this chapter, designing a system based on your needs is first approached by Defining  
And Meeting Your Needs. This topic is designed to help you choose or at least  
understand the system. IFB is described in The IFB System (One Way Communications  
System). Then Connecting (Interfacing) to Other Communications Systems discusses  
real world solutions to interfacing these systems. The Some Practical Considerations  
section discusses real world environments and some work-arounds. A Summary closes  
this chapter.  
Defining And Meeting Your Needs  
Your needs could include buying, renting, assembling or expanding a system. Application  
Block Diagrams are a good starting place to define a system. In this section, block  
diagrams of applications in each of the three leading systems will be shown and discussed.  
These diagrams will range from relatively simple to complex systems. One of these block  
diagrams could be close to what you need to know, give or take a station or so. If you  
make a copy of the diagram and mark it up, this could define your system.  
Disclaimer The block diagrams are for instructional purposes, and though every effort has been for  
accuracy, the manufacturers offerings are often changing. It pays to double check with the  
manufacturer or rental house to verify the exact system available before buying or renting.  
Application 1 Generic Single Channel Systems  
The first applications are generic single channel systems, see Fig.1.3. They consist of a  
power supply, belt packs, headsets, splitter boxes, and microphone cables. These are  
systems that could be used in a small television studio production, a small outside  
television field production, or an industrial test of a large system. Depending on the detail  
of the block diagram, you may be able to compile an equipment list from this diagram.  
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Audiocom Party-Line Intercom Equipment Listing #1  
Figure 3.1 Generic single channel Audiocom® system.  
Power Supply: PS2001L  
Splitters: TW5W  
Belt Packs, Single Channel: BP1002  
Headsets: Leader Person: Single Muff PH-1; rest of crew: Double Muff PH-2  
Cables: Standard Microphone Cables with XLR-3 connectors  
The first block diagram, Figure 3-1 shows a simple single channel Audiocom intercom  
system. We start with a 2-channel PS2001L phantom power supply, two TW5W splitter  
boxes, two strings of three each single channel BP1002 belt packs, one PH-2 single muff  
headset and five PH-2 double muff headsets.  
Note A switch on the PS2001L power supply allows both channels to be combined for one large  
Party-Line.  
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Clear-Com Party-Line Intercom Equipment Listing #1  
Figure 3.2 Generic single channel Clear-Com® system.  
Power Supply: PK-5  
Splitters: TWC-10A  
Belt Packs, Single Channel: RS501  
Headsets: Leader Person: Single Muff CC-95; rest of crew: Double Muff CC-260  
Cables: Standard Microphone Cables with XLR-3 connectors.  
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RTS TW Party-Line Intercom Equipment Listing #1  
Figure 3.3 Generic single channel RTSTW system.  
Power Supply: PS15  
Splitters: TW5W  
Belt Packs, Single Channel BP319  
Headsets: Leader Person: Single Muff PH-1R; rest of crew: Double Muff PH-2R  
Cables: Standard Microphone Cables with XLR-3 connectors.  
Application 2 Two-Channel System: TV, School, Cable  
The second application is a two-channel system for a small TV operation (Studio or  
®
®
Truck), school or cable access. The Audiocom and Clear-Com systems will require  
two 3-conductor microphone cables between director, switcher, video, and graphics. The  
RTS TW system only requires a single microphone cable for all hook-ups.  
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Figure 3.4 Small TV operation.  
Audiocom Party-Line Equipment Listing #2  
Power Supply: PS2001L (Rack Mount, 1RU)  
Director’s Station: US2002 (Rack Mount, 1RU)  
Video: WM2000 (Wall Mount)  
Graphics: WM2000 (Wall Mount)  
Cameras and Floor Manager: BP1002 (Belt Packs)  
Headsets Director, Switcher, Floor Manager, Video, Graphics: Single Muff PH1  
Headsets: Cameras: Double Muff PH2  
Splitter: TW5W IFBs: IFB-1000  
Earphones (Earsets): CES-1  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per channel.  
Note /2 indicates two microphone cables & /1 indicates one microphone cable.  
Clear-Com Party-Line Equipment Listing #2  
Power Supply: PS22 Rack Mount with RK-101 kit (2RU)  
Director’s Station: RM220 (Rack Mount, 1RU)  
Switcher’s Station: RM220 (Rack Mount, 1RU  
Video: MR202 Wall Mount (2-gang box)  
Graphics: MR202 Wall Mount (2 gang box)  
Cameras and Floor Managers: RS-501 (Belt Packs)  
Headsets Director, Floor Managers, Video, Graphics: Single Muff CC40  
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Headsets: Cameras: Double Muff CC60  
IFBs: TR-50 (Includes earset)  
Splitter: TWC-10A  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per channel.  
Note /2 indicates two microphone cables required.  
RTS TW Party-Line Equipment Listing #2  
Power Supply: PS31 Rack Mount (2RU)  
Director’s Station: MCE325 (Modular Mount: Rack/Desk/Console (1RU)  
Switcher’s Station MRT327 (Modular Mount: Rack/Desk/Console (1RU)  
Video: WM300L: Wall Mount (2 gang box)  
Graphics: WM300 Wall Mount (2 gang box)  
Cameras and Floor Managers: BP351 Belt Packs  
Headsets Director, Floor Managers, Video, Graphics: Single Muff: PH-1R  
Headsets Cameras: PH-2R  
IFB’s: IFB325 Earsets: CES-1  
Splitter: TW5W Cables:  
Standard Microphone Cables with XLR-3 connectors. One cable per two channels.  
Note Ignore /2, both channels are in one microphone cable.  
Application 3 Theater System  
Figure 3.5 Theater application.  
The third application is a theater application, see Figure 3-5. A two-channel system is used  
in this application. Channel A connects the crew together and channel B is used by the  
stage manager to cue the actors. This is done using three wall mount or portable speaker  
stations. For all three systems, only standard microphone cable is required. In the case of  
the RTS TW system, Channel B is available to the crew, but except for rehearsals or set-  
up they would stay on Channel A.  
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Audiocom Party-Line Equipment Listing #3  
Power Supply: PS2001L (Rack Mount, 1RU)  
Stage Manager’s Station: US2002 (Rack Mount, 1RU)  
Dressing Rooms and Green Room: SS1002 (Single channel wall mount station; if a  
portable speaker station is desired, add an S, U, or P box).  
Crew: BP1002 (Single Channel Belt Packs)  
Headset: Stage Manager Single Muff PH1  
Headsets: Crew: PH2  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per channel.  
Clear-Com Party-Line Equipment Listing #3  
Power Supply: PS22 Rack Mount with RK-101 kit (2RU)  
Stage Manager’s Station: RM220 (Rack Mount, 1RU)  
Dressing Rooms and Green Room: KB-212 (Single channel wall mount speaker station, if  
a portable speaker station is desired, add a V-Box portable enclosure.)  
Crew RS-501 (Single Channel Belt Packs)  
Headset: Stage Manager: Single Muff CC40  
Headsets: Crew: Double Muff CC60  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per channel.  
RTS TW Party-Line Equipment Listing #3  
Power Supply: PS31 Rack Mount (2RU).  
Floor Manager’s Station: MRT327 (Modular Mount: Rack/Desk/Console (1RU).  
Dressing Rooms and Green Room: SS1002 (Single channel wall mount speaker station).  
Crew: BP319 Belt Packs (Set to work on Channel A).  
Headset: Stage Manager: Single Muff: PH-1R.  
Headsets: Crew: PH-2R.  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per two  
channels.  
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Application 4 Training Systems  
Audiocom  
Figure 3.6 Audiocom® based training intercom system.  
The training system consists of an instructor and multiple two-student crews.  
In the case of Audiocom, each of the six two-student groups are independently addressable  
by the instructor. When the student groups are not talking to the instructor, each two-  
student group can have semi-private conversations. The call light tells the instructor which  
group is paging. The balanced Audiocom system is ideal in hostile electrical noise  
environments.  
Power Supplies: SPS2001 and PS4001.  
Instructor’s Station: US2002 and Expansion Station.  
Students’ Stations: BP1002 Single Channel Belt Packs.  
Instructor’s Headset: PH-1, Single muff headset.  
Students’ Headsets: PH-2, Double muff headsets.  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per channel.  
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Clear-Com  
Figure 3.7 Clear-Com® based training intercom system.  
®
It just happens that the Clear-Com system is the simplest for this application, since the  
Master Station, MS-812A has the three pin XLR connectors for 12 channels on the rear  
panel. The MS-812 has several configurations, and will have to be specified for this  
application (No IFB, 12 Clear-Com standard PL channels).  
Power Supply: PS-464.  
Instructor’s Station: MS812A.  
Students’ Stations: Single Channel Belt Packs RS-501.  
Instructor’s Headset: Single Muff CC-95.  
Students Headsets: CC-250.  
Cables: Standard Microphone Cables with XLR-3 connectors. One cable per channel.  
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RTSTW  
Figure 3.8 RTSTW based training intercom system.  
The RTS TW system for this application is the next simplest, and has added features.  
The student crews can have completely private conversations, yet are still reachable via  
the call light paging system. Each BP325 belt pack can be configured to accept an  
individual program source (but the loop-through is lost and the two students line  
connection will be through a simple one to two splitter). The program source is often a  
training audio/video tape, along with a monitoring computer tests the reaction time and  
correctness of the students reaction.  
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Application 5 Medium System for Television  
Figure 3.9 Medium intercom system for television.  
This shows an RTS TW large 12-channel system. This is a system that is in medium  
trucks that haven’t yet switched over to a combination matrix and Party-Line system. This  
system consists of five Model 803 Master Stations, four PS31 Power Supplies, one  
SAP1626 Source Assign Panel, a BOP220 Break Out Panel, a VIE Video Isolate Panel, a  
four belt pack Telex BTR600 Wireless Intercom, and various belt pack and other user  
station. Also are interfaces to a telephone and a satellite communication link. Many trucks  
®
have a similarly configured Clear-Com system. The Master Stations are usually for: the  
Director, Assistant Director, Lighting Director, Audio Mixer and Video operator (the one  
with the VCP6A isolate panel. No IFB (Interrupted FeedBack) is shown in Figure 3-9, but  
an IFB system is easily married to the Master Stations. A large RTS IFB add-on is  
shown in Figure 3-10. Note that Model 4020 is now Model 4030. Similar IFB systems are  
available from Clear-Com and Audiocom. The Control Station connects to the “Hot Mic”  
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output of a Master Station or User Station with a “Hot Mic” output. The IFB electronics  
receives its program audio from the audio mixer board.  
The IFB System (One Way Communications System)  
IFB is a television acronym for Interrupted FeedBack, Interrupted FoldBack, Interrupted  
Return Feed (IRF). An IFB system permits a director or producer to talk to the talent,  
typically an “on air” announcer, newscaster, or sportscaster. Normally the talent hears the  
broadcast program audio. When the director or producer activates the IFB, the program  
audio is replaced by the director’s or producer’s voice. Sometimes the program audio  
continues in the other ear, sometimes the program audio is reduced instead of completely  
removed.  
How an IFB Works  
Those in control positions (the director, producer, or assistant director for example)  
control the interrupt and or announce functions via control stations. Those in receive  
positions (on-air talent, floor managers, studio or field crew, audience, talent and crew in  
remote locations) are on the receiving end of the user station feed or on the actual user  
stations (talent electronics or talent station) via headphones, headsets, earphones, and / or  
loudspeakers. In the middle, the central electronics unit provides all the necessary inputs  
and outputs, processing, switching, and power distribution.  
Studio and Some Field Applications  
Note Model numbers of the different parts of the IFB are as follows:  
Control Panel  
®
Audiocom : Built into US2002, ES4000A. Clear-Com: MA-4, AX-4. RTS TW:  
Models 4001, 4002, 4003  
IFB Electronics  
®
Audiocom : Built into US2002, ES4000A; Clear-Com: PIC4000B; RTS TW: Model  
4010  
Talent Receiver  
®
Audiocom : IFB1000; Clear-Com: TR-50; RTS TW: Model 4030  
Earset  
Audiocom: CES-1; Clear-Com: (part of Model TR50); RTS TW: CES-1  
In non-sports activities, the talent normally uses only the interrupt output (mono) of a  
Talent User Station. The earphone is hidden behind the talent’s back; a plastic tube runs  
from the earphone to the talent’s ear.  
Field Application, Sports  
In the sports broadcasting or sports communication field, the talent uses a noise resistant  
headset. The microphone on the headset is the “air” microphone; the headphone is double  
muff, stereo. The talent is plugged into the stereo output of (for example) the Model 4030  
Talent Receiver User Station. At the IFB Control Station, each talent’s name is marked on  
a strip of tape pasted adjacent to the push buttons.  
In stadium sports, there is usually little problem in getting a microphone cable from the  
IFB Electronics to the Talent Receiver. In the case of golf, auto racing, and sports venues  
over an extended area, the distances may be too great. In this case, a four wire circuit can  
be run to the talent location and adapted to the connector on the Talent Receiver.  
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In some more extreme cases, only a single pair of wires may be available. In this case, plug  
the talent’s stereo headset into the stereo connection on the talent receiver, then connect  
the high side of the pair to pins 2 and 3 of the XLR3 connector and the low side to pin 1  
(pseudo-stereo mode). This will give a mono feed with each ear individually adjustable  
and both ears interrupted.  
For runs of two miles of number 22 gage twisted pair, at least one talent receiver station  
should be operable. For a run of one mile, two talent stations should be operable.  
Some users have increased the number of talent stations by using higher impedance (300  
ohms) headsets. In the case of auto racing and similar loud environment situations, low  
impedance noise isolating headsets will be necessary to overcome the volume and amount  
of sound. It may be necessary to use a four wire circuit to connect up each talent station,  
paralleling the pairs, and running the talent receiver in pseudo-stereo mode, using only the  
interrupt (“wet”) output of the IFB electronics.  
Field Application, ENG (Electronic News Gathering)  
In this case, the earphone is again hidden as in the studio case above. If the talent has to  
carry on a conversation with other talent at the studio and other venues, the program feed  
should be a mix minus feed. The mix minus feed will allow the talent to hear the other  
talents loud enough without hearing their own self too loud.  
Connecting (Interfacing) to Other Communications Systems  
What is interfacing? Interfacing is either:  
1 The interconnection of two normally separate communications systems into one  
system.  
-OR-  
2 The connection of a communications station or device that is not directly compatible  
within a system.  
To accomplish this, voice and data information is adjusted and then transmitted to the  
other system. The adjustments include level translation, impedance compensation, mode  
translation, and compensation for parameters of each system.  
Some examples are:  
1 System to system: connection of a four-wire matrix system installed on a large mobile  
unit to two-wire belt packs outside of the mobile unit.  
2 System to terminal: connection of a camera with a built-in intercom to an intercom  
system, or connection of a radio transceiver into an intercom system.  
Why is there interfacing, operationally? From an operations point of view:  
1 An operation requires a larger collection of personnel and equipment than normal.  
2 A mobile unit is used with a permanent installation to conduct an operation.  
3 Coordination between personnel / equipment is required at a remote location.  
4 A special part of the operation requires communication with an odd system or terminal.  
5 A redundant “backup” path is required.  
Why is there interfacing, technically? There are system to system, system to terminal or,  
system to device differences.  
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Some of these are:  
1 Mode differences. There are several not directly compatible modes of operation: two  
wire mode, four wire mode, full duplex mode, half duplex mode, simplex mode.  
Examples: the TW System is two-wire full duplex, the ADAM matrix is four-wire  
full duplex, the telephone is two wire full duplex except some long distance calls are  
half duplex (both people cannot talk at once), a walkie talkie is simplex, AudioCom is  
two-wire full duplex, Clear-Com is two-wire full duplex, office intercoms are often  
simplex operation.  
2 Level and Impedance differences. System voltage levels range from - 40 dBu to + 21  
dBu with peaks to +28 dBu (where 0 dBu = 0.7746 volts). See Table 3.1, for typical  
ranges.  
Table 3.1 Typical system impedances and ranges.  
Nominal  
Impedance  
(Ohms)  
Nominal Level  
Intercom or  
Audio System  
Level  
(dBu)  
Range  
(dBu)  
Telephone  
600 to 900  
200, 10k  
200, 10k  
300, 10k  
200, 10k  
600, 10k  
-15  
-30  
-14  
0
-40 to 0  
Old Clear-Com  
New Clear-Com  
Audiocom  
-45 to -15  
-14 to +5  
-8 to +1  
RTSTW  
-10  
+4  
-10 to -1  
-6 to +24  
Recording Studio  
There are different modes of intercom operating modes because each mode offers a  
different advantage for different needs and situations. For example, two-wire is quick and  
easy to hook up, while four-wire is easier to interface to other systems.  
A Typical Interfacing Problem  
A television camera uses a triax cable to connect the camera to the rest of the electronic  
system because a triax cable allows operation over longer distances with more consistent  
quality. This is because the triax cable uses radio frequencies to transmit information both  
ways on the cable. This is, in effect, four-wire (two path) communication. The following  
implementations often need interfacing:  
1 Television camera intercoms to intercom systems.  
2 Two-wire systems to four-wire systems.  
3 Full duplex systems to simplex systems.  
4 When transmission medias change.  
Interfacing Issues  
There are three tasks to interfacing:  
1 Mode Conversion.  
2 Level Problems.  
3 Signal / Data Conversion.  
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Modes  
The following modes exist in intercom systems:  
M2) Two-Wire.  
M4) Four-Wire.  
The following sub-modes are considered for two-wire and four-wire:  
M2F) Two-Wire, Full Duplex.  
M2H) Two-Wire, Simplex.  
M4F) Four-Wire, Full Duplex.  
M4H) Four-Wire, Simplex.  
Level Problems  
One problem in interfacing from two-wire to two-wire is caused by the 2 wire systems’  
use of 2 to 4 wire hybrids. Interfacing requires conversion from two-wire to four-wire  
twice to allow level adjustments to and from systems. The quality of the two-wire to four-  
wire hybrid limits the amount of make-up gain available to match levels in one system or  
the other.  
Another problem with interfacing is that level adjustment is difficult when interfacing  
from a limiter controlled system, such as the TW Intercom System, to a non-limiter  
controlled system, such as some two or four wire systems. The reason for the difficulty is  
that the perceived loudness is greater on the TW System and much less on the non-limiter  
controlled system. This difference can be improved or eliminated depending on two  
limiting factors: 1) the headroom of the electronics involved, and 2) the quality of any two-  
wire to four-wire hybrids in the path. Interfacing from two-wire to two-wire systems is the  
most difficult. Interfacing from two-wire to four-wire is easier, and interfacing from four-  
wire to four-wire is the easiest. The problem in two-wire / two-wire interfacing is getting  
the levels right and preventing oscillations.  
The level of the TW and 800 Series conference intercom systems ranges from -10 dBu to  
0 dBu, with an average value of - 6 dBu, and is limiter controlled.  
Some other systems are listed in Table 3-2. The objective is to convert the modes and to  
adjust the levels.  
Signal / Data Conversion  
Call Light  
Some intercom systems use a “Call Light” signal to illuminate lights in individual stations.  
This signal may be a 20 kHz tone, a DC level, or a digital logic level. An interfacing  
device may handle the method conversion to carry the call light signal.  
Data  
Other systems have data flow via various methods including: contact closure, logic level,  
RS485 bus, RS422 bus, and RS232 bus. The handling of the RSxxx signals is done best on  
a case-by-case basis. At this point, system-to-system communications is done via RS232  
communications by wire, fiber optic, or telephone lines via modem. Some system-to-  
system communication is accomplished through user specified hardware imbedded in  
special products.  
Some Master Stations have an RS232/485 connection that allows control of the station  
over a terminal or another computer.  
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Interfacing Practice  
Interfacing Television Camera Intercom Systems to TW Systems  
General Camera Configuration Information for Television Cameras (except ENG  
units)  
Television cameras used in broadcast and industry usually have two parts: a camera head  
and a camera control unit (CCU). The camera head assembly usually contains the lens  
equipment, camera electronics, and triax adapter (if used). The CCU contains additional  
electronics for processing video, the other end of the triax adapter, an interface for  
microphone audio, and the intercom interface. The intercom interface usually incorporates  
switches and electronics so that the intercom can be two-wire or four-wire.  
The Problems in Interfacing to Cameras  
There are two problem areas in television camera intercoms:  
1 The electronics in the camera head.  
2 The intercom interfacing electronics at the CCU.  
Some possible problems with the camera head intercom electronics are as follows:  
Inadequate headphone drive (Not loud enough for athletic contests and studio  
shows)  
No limiter in the microphone preamplifier (level variations are too much)  
The headphone and the microphone share a common circuit return conductor  
(headphones oscillate when volume is turned up)  
The Triax Adapter / electronics does not give the camera intercom enough  
headroom, so there is a trade-off between signal clipping and signal to noise  
ratio.  
The microphone on/off switch does not disconnect the microphone preamplifier  
thus adding noise to the system.  
Some possible problems with the CCU intercom interface electronics are:  
An earth ground is applied to the wiring usually in two-wire mode (causes hum  
loops in the system)  
The four-wire input to the camera is not bridging impedance  
The two wire “RTS0153 Systems compatible” interface loads the line  
No safety capacitors are installed in the CCU, thus causing burnt transformers if  
connected to the intercom line  
Alternatives for Interfacing to Television Cameras  
1 Bypass the camera, tape a microphone cable to the camera cable, and plug a TW belt  
pack in at the end.  
2 Use the existing camera intercom, interface it to the TW system with a Model SSA324  
or SSA424 interface (if camera intercom is four-wire).  
3 In multi-core connected cameras, use the camera wiring to allow a TW belt pack to be  
plugged into the camera head. This allows the camera operator to use a portable User  
Station mounted on his belt or attached to the camera body. (  
Note: This requires significant modification to the camera head and CCU)  
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Table 3.2 Intercom comparisons.  
Nominal  
Impedance  
Estimated  
Peak TX  
TX/RX  
Levels  
Intercom Impedance Range  
Output  
Type  
Type  
(Ohms)  
(Ohms)  
Mode  
Power (mW) (dBu)  
TW  
200  
50 to 400  
600 to 900  
100 to 1k  
600 to 10k  
4 to 150  
Un-Bal two-wire  
Bal two-wire  
5
1
0 to -10  
0 to -10  
-10 to -20  
+8  
TELCO  
Two-Wire  
Four-Wire  
600  
150 to 200  
600  
Un-Bal two-wire 0.7  
Bal  
four-wire  
7
2
Carbon Mic 150*  
Un-Bal two-wire  
0 to -30  
TELCO = Telephone-lines in two-wire mode  
Two-wire = Clear-Com, ROH, HME, R-Columbia, Protech, Theatre Techniques, Telex**,  
some television cameras  
Four Wire = RTS ADAM intercom, Philip Drake, Link, McCurdy, Ward Beck, ADM,  
Farrtronics, PESA, Audix, Datatronics, all triax television cameras, some multi-core  
television cameras, Radio-telephones, Telephone-Line circuits, Wireless Intercom systems  
Carbon Mic Interphone = RCA, Daven, Video Aids, General Electric, Colorado Video,  
many low-cost television camera intercoms  
* Per Station  
** Telex(r) Phase 2 = 300 ohm, 5 mW balanced line.  
Some Practical Considerations  
Headset Cable Lengths  
The dynamic (low level) headset cable carries signal levels that differ by as much as 34 dB  
+ 52 dB = 86 dB. Ordinarily, there are three types of unwanted coupling possibilities:  
resistive (through a common ground), capacitive and inductive. Since separate grounds are  
carried back to the microphone preamplifier and headphone amplifier, the common ground  
resistive coupling is, in this design, negligible. The capacitive coupling can be made non-  
significant by a 100% shield in the cable. The inductive coupling mode dominates in this  
design, and can be offset in several ways:  
• The distance between the microphone and headphone pairs can be increased, while the  
mutual inductive coupling is decreased by the use of “ribbed” cable (two cables molded  
together side-by-side).  
• Both the microphone cables and the headphone cables can each be tightly twisted.  
• Two or four separate cables can be run. A balancing transformer on the microphone  
circuit may be used. Estimated, Safe Operating Distances are as follows:  
• Single cable, two shielded twisted pair: 10 feet.  
• Dual ribbed cable, two shielded twisted pair: 30 feet.  
• Separate cables, shielded twisted pair in each: 50 feet and more.  
• Balanced microphone input: up to 100 feet depending on cable used.  
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Headphone Impedances  
Low impedance headphones are louder, causing the user station to draw more current from  
its power source. High impedance headphones are not as loud, drawing less current. Many  
user stations have a headphone impedance range from 25 - 600 ohms.  
Headphones up to 2,000 ohms will function but greatly reduced levels. In a double muff  
headset such as a Beyer DT-109, there are two 50 ohm headphones connected in parallel  
resulting in an impedance of 25 ohms.  
Wiring Practices/Workmanship Standards  
The two most significant wiring practice/workmanship problems are as follows:  
1 Unintentional grounding, phase reversals (channel reversing) and power reversal. Cable  
shields must not touch connector shells or be tied to the connector shell lug. Cables  
(especially the vinyl insulated type) must not be pulled tight around sharp edges.  
2 Line noise due to an intermittent connection:  
Poor solder joint.  
Corroded connector.  
Loose screw terminal.  
An non-insulated cable shield touching the metal shell of the connector.  
Portable user stations should not arbitrarily be taped or fastened to metal structures.  
Grounding the case of the user station to an arbitrary structure may introduce large noise  
voltages due to local ground currents or due to the completion of a “ground loop antenna”.  
Phase reversals are most common with portable microphone cable that has not been  
checked with a standard cable tester after fabrication or repair.  
DC power reversals are usually not harmful to user stations since there is normally a  
protective diode in the circuit. The station simply doesn’t work. Remember: negative is  
ground in this system.  
Always clear all earth grounds from the RTS™ TW System circuit return ground.  
The only ground should be the 22,000 ohm resistor in the power supply.  
Unbalanced vs. Balanced  
Intercom systems such as the TW System, in the standard, unbalanced configuration have  
been operated at distances of up to two miles with acceptable system noise levels. Routing  
the intercom cables along the same ductways and pathways as the main power cabling can  
increase the noise and hum levels in the system.  
If intercom cables have to be routed in this manner at distances over 300 meters (1,000 ft.),  
a balanced conversion should be made.  
Alternatively, the entire system can be operated in an optional balanced mode and be  
powered at each station with the “local power” option. This is sometimes called “dry line,  
balanced” operation.  
Extended Range On Part Or All Of The System  
If a station is locally powered, operational range can be extended up to five miles, using  
two transformers to step up the line impedance to 800 ohms (for lower losses). When the  
users station has the four wire / 800 ohm option installed, operation is possible up to 20  
miles along Telco dry pairs. Operation over longer distances (3000 miles) is possible using  
dial up or minimum loss dry lines and the TW series of interfaces.  
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Cable Considerations  
Crosstalk  
Use shielded cable to interconnect user stations in areas of possible electrical interference,  
(areas such as those near: digital equipment, high current primary power conductors  
“power outlets”, transformers, transmitters, and lighting dimmers. Do not run TW  
Intercom System cables along the same ductways and pathways as these cables.  
Standard wire size for the an intercom system interconnection is #22 gauge shielded cable,  
such as Belden 8761, 8723, 9406.  
In permanent installations, to reduce both capacitive and resistive crosstalk and to afford a  
degree of RF and electrostatic shielding use a cable that has a shielded twisted pair for  
each channel, such as Belden 8723. Each pair consists of a conductor for the channel, a  
conductor for circuit ground return and shield around the two conductors. The shield is  
accessed via a drain conductor. This drain conductor and the shield can augment the circuit  
grounds and thus lower the ground resistance. Do not tie the shield to chassis, earth, or  
connector shell ground.  
Crosstalk Through A Common Circuit Ground  
Since, in the unbalanced version of a TW intercom, all channels share a common circuit  
ground return, crosstalk due to common ground resistance can occur. This crosstalk is  
proportional to the ratio of the common ground resistance to the system terminating  
impedance, 200 ohms. This occurs when a talker on one channel is heard by a listener on  
another channel due to the common ground resistance (see Figure 8-4). Reduction of this  
crosstalk can be accomplished by reduction of the circuit ground resistance. Reduction of  
the ground resistance can occur as a side benefit of using shielded cable, since the shield  
drains can be tied together and electrically parallel the circuit ground.  
Another way of lowering this kind of crosstalk is to “homerun” all interconnecting cables  
to a central or “home” location. This causes the common circuit ground path to be very  
short, and other things being equal, makes a low common ground resistance.  
Crosstalk Through A Mutual Capacitance Of Two Conductors  
Two conductors such as a twisted pair can accumulate a large mutual capacitance over  
long distances. Using a figure of 100 picofarads per meter and a distance of 1 kilometer,  
results in a total capacitance of 100 nanofarads or 0.1 microfarad. The reactance of 0.1  
microfarad at 800 hertz is 2000 ohms. Referred to the system impedance of 200 ohms, the  
apparent crosstalk is about 20 log (200/2000) or about -20 dB. Separating the two channel  
conductors by a shield greatly reduces the capacitive crosstalk, so that the resistive  
crosstalk discussed above dominates.  
A Low Crosstalk Approach To Interconnection  
To reduce capacitive and resistive crosstalk and to afford a degree of “RF” and  
electrostatic shielding, a shielded, twisted pair per channel type cable can be used. Each  
pair consists of a conductor for the channel, a conductor for circuit ground return and, of  
course, the shield as a conductor and the shield drain conductors. These drain conductors  
and the shield can augment the circuit grounds and, thus, lower the ground resistance.  
Distances/Conductor Sizes/Distributed vs. Central Connection  
Systems that stretch over distances of kilometers are more subject to power losses and  
crosstalk. These problems can be minimized through the use of large enough wire,  
shielded cables and central connections.  
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System Current/System Capacitances/Loading  
The system currents are determined by several parameters:  
1 The current required to supply standby current for each user station.  
2 The current required to supply the dynamic current to generate line signal, headphone  
signals, speaker signals and call lamp signals.  
3 The current required to start up a system (inrush current) by charging up to (50) 4000  
microfarad capacitors or 0.2 farad.  
4 The current limit imposed by the power supply to protect itself.  
5 The secondary current limit imposed by the power supply when a fault is close to the  
power supply (little or no circuit resistance). This limit, called the foldback current,  
further protects the power handling electronic devices in the supply and determines the  
system start-up time.  
Currents 1 and 2 can be calculated by multiplying the number of user stations times the  
user station current data in the Complete User Station Specifications. Current 3 is usually  
limited by current 5. Currents 4 and 5 are listed in the Power Supply Specifications.  
Current 5 can be used to calculate the system start-up time: where:  
T is the start-up time (approximated) in seconds.  
N is the number of stations.  
C is the capacitance per station = 4 millifarads  
i is the power supply foldback current  
dV is a change in voltage across the capacitors, say 10 volts.  
For a 20-station system, a 1 ampere foldback current, and a 10 volt change on the  
capacitors:  
The actual system start-up time will be longer since voltages in each user station have to  
stabilize before audio can be transmitted. This time is on the order of several seconds.  
Temperature Range Consideration  
All of the elements of the TW Intercom System have been designed to operate over the  
temperature range of 0 degrees Celsius (32 degrees Fahrenheit) to 50 degrees Celsius (122  
degrees Fahrenheit). The high temperature range is extended another 15 degrees Celsius if  
the units are not operating at full capacity or some other worst-case condition. The low  
temperature range is extended another estimated 20 degrees Celsius if the full system gain  
range is not required. The major operating problem at lower temperatures will be the dew  
point and the resultant condensation. If this is the typical operating environment, then it is  
recommended that the equipment be opened, cleaned, dried and sprayed with several light  
coats of plastic spray. This will lessen the noises generated by leakage currents that occur  
when the moisture and any dirt or film combine. Cleaning can be accomplished a rinse of  
alcohol, a very mild detergent (saponifier type) wash and 2 or 3 thorough rinses with  
distilled water. This routine is to first wash off the nonpolar soluble substances, then the  
polar soluble substances.  
Cooling Requirements  
In general, only the power supplies require cooling consideration. Normally, leaving 2  
inches clearance above and below the rack-mounted supplies is adequate. Portable  
supplies should not be left in the sun and these supplies should have clearance of 6 inches  
from five of the six surfaces. All other elements of the TW Intercom System require no  
special consideration. It is important to note that belt packs and other equipment left in the  
sun can cause burns to human flesh, due to the large amount of heat transfer possible. The  
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user stations will normally continue to operate if one can only figure out a way to flip the  
switches and touch only the knobs.  
Moisture / Contamination Protection  
If, in the field, a soft drink or something like it is spilled into the equipment, the equipment  
can be dismantled and cleaned gently with clean water. After the equipment is dry it can be  
returned to service. If this happens fairly often, residues in the water can be deposited on  
the equipment. It should be noted that a build-up of contaminates and humidity can cause  
audible noise on the intercom line. If it is likely that the equipment is continually to be  
exposed to contaminating liquid, suitable plastic covers should be employed. It may also  
be necessary to add a plastic coating as described above. When using equipment in the rain  
always protect the equipment with plastic covers - also, make sure all cable connectors are  
lifted out of the mud or snow and protected with plastic bags. Rain, mud and snow in  
connectors can cause considerable audible noise in any communications system.  
Magnetic Fields: Hum Problems  
When the balanced type of intercom equipment is used, it is still possible to induce hum  
into the system by placing or locating user stations or system interconnects near a hum  
source, such as, power transformers or electrical switch panels or lamp dimmers. When the  
microphone switch is turned on and a dynamic microphone headset is used, the dynamic  
microphone is a sensitive antenna for magnetic fields. Often, operating personnel will go  
on a break, leave the microphone on and lay the headset on equipment with power  
transformers or near TV cameras or monitors with vertical deflection yokes. This is the  
reason for the system microphone turn-off scheme (Mic Kill).  
SUMMARY  
(Defining and Meeting Your Needs)  
1 Application Block Diagrams are a good starting place to define a system.  
2 The generic block diagrams show a basic small system and how things plug together.  
3 A generic system could used in a small television studio production, an outside  
television field production (such as ENG and EFP) or an industrial test of a large system  
(such as an aircraft).  
4 A generic system can be created using almost any Party-Line system. Audiocom, Clear-  
Com, and RTS TW systems block diagrams are shown.  
5 A switch on the Audiocom PS2000 two channel power supply can combine channels  
into one large Party-Line.  
6 Equipment available from any one of the three illustrated manufacturers intercom  
systems can be assembled into a two-channel system.  
7 A two-channel system can be used for a small TV operation (Studio or Truck) or cable  
access. One channel can be used for the director and crew, and the other channel can be  
used as a public address or stage announce system. The stage announce system can cue  
talent for the show, or allow the director to talk to the performing crew and talent during  
rehearsals.  
8 All three manufacturers make equipment suitable for theater applications use. Again,  
one channel of a two-channel system can be used to cue the actors.  
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9 A training system usually consists of a station for the instructor and multiple,  
independently addressable student stations.  
10In a large system for television production, additional accessory equipment allow  
expanding the Party-Line into 12 or more Party-Line channels, isolated camera  
channels, IFB capable stations, and wireless intercoms.  
(The IFB System (One Way Communications System))  
1 IFB is an acronym for Interrupted FeedBack, Interrupted FoldBack, or Interrupted  
Return Feed (also known as IRF).  
2 An IFB system allows people running the show, such as director, producer, and mixer  
to talk to the talent or actors directly. The talent may receive cues, additional  
information, or hear other talent in other locations to be able to talk with them.  
3 The IFB system consists of a 1) a hot mic feed from a director, producer, et cetera, 2) a  
control panel, 3) connecting cables, 4) talent station, 5) talent headset or earset. Some  
IFB systems are wireless. This requires some different equipment, and the wireless  
feature eliminates the connecting cables.  
4 IFB systems are often required to operate over large systems, as much as a mile.  
(Connecting (Interfacing to Other Communications Systems))  
1 Interfacing is connecting two separate communications together or not directly  
communications to the Party-Line.  
2 One modern interface requirement is two connect a two-wire Party-Line system to a  
four-wire intercom system.  
3 Interfaces often can compensate for system to system: a) level differences, b) mode  
differences, c) impedance differences, and can translate call light and other data signals  
into suitable formats.  
4 Interfacing to various television cameras is often challenging and may require extra  
equipment and extra efforts.  
5 There are three tasks to interfacing: mode conversion, level changing, and signal / data  
conversion.  
(Some Practical Considerations)  
1 A too long headset cable may cause feedback or crosstalk problems.  
2 Low impedance headphones, in general are louder and cause the user station to draw  
more current. Higher impedance headphones lower current drain but may not be loud  
enough for use during concerts or athletic contests.  
3 Accidental connection of the shield in a microphone cable to earth grounded objects  
may cause hum and noise in the intercom system.  
4 Taping or fastening metal intercom stations to metal structures may introduce into the  
Party-Line intercom system.  
5 Cabling in poor condition may introduce noise / intermittent operation into a system.  
6 It may be necessary to convert the intercom audio to a balanced configuration to cover  
long distances or to overcome strong interference from adjacent cables.  
7 Extending the range of the Party-Line intercom may require using heavier gage cables,  
or using special schemes of “local powering” the remote user station.  
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8 Extending the range and using “local powering” may reduce a two-channel system to  
one channel at the remote station.  
9 Crosstalk in a two channel system such as the RTS TW system can be reduced by  
“home running” the cables to a central point where the splitters and power supply are.  
10Crosstalk can also occur across the ground connection, especially where long cables  
have built up the ground resistance.  
11System currents are defined by the type of user station, its current drain, and the number  
of stations on a power supply feed.  
12If the system is operated too close to its maximum current, it may have trouble starting  
due to the “foldback” current limiting in a power supply. The work around for this is to  
break the system into several subsystems, then power up each subsystem in sequence.  
13Temperature Range Consideration: Condensation due to low temperatures may cause  
noise in a system.  
14The power supplies are generally very rugged and withstand a wide range of  
temperatures. But it is still important to take precautions to prevent overheating of the  
power supplies.  
15The dynamic microphone in a headset can pick up stray magnetic fields and introduce  
unwanted hum and noise into a system. Don’t place the headset on or near other  
equipment that has strong magnetic fields.  
16If equipment gets contaminated with a spilled drink, mud or snow, it may require  
cleaning with distilled water and gentle drying.  
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C H A P T E R  
4
C
HAPTER 4  
INTRODUCTION TO MATRIX  
INTERCOM SYSTEMS  
RALPH STRADER  
Introduction  
While there is an extensive glossary in the back of this book, some definitions will be  
given here to aid in the following chapter.  
Definitions  
Ports Refers to the number of connections available to external devices from the matrix. In  
typical usage a logical port consists of an audio input to the matrix, which is used to bring  
the talk signal from a user station, an audio output used to take listen audio to the same  
panel, and a bi-directional data signal for control and status information between the  
matrix and the user station. In the RTS™ ADAM™ intercom system, the inputs and  
outputs can be assigned to completely separate functions, allowing the port to be “split.” A  
typical application would use the output portion of a port for a feed to a paging speaker,  
while using the input portion to provide program audio to be used with IFB feeds.  
Matrix The audio router that establishes communications paths from user to user. A matrix must  
not only provide the routing, it must do so reliably, remembering configuration and status  
and reporting on them. They must also have some degree of reliability – which, as with all  
things in the world, is related to needs and budget.  
User Station Also referred to as a keypanel. Using the telephone system analogy, the matrix is the  
central office switch or PBX and the keypanel or user station is the telephone instrument.  
These devices can range in complexity from a simple microphone with a single push  
button and a loudspeaker to a fully programmable keypanel with alphanumeric displays,  
DSP signal processing, user programmable features and volume controls. The RTS™ KP-  
32 (see figure 4.1) is a good example of the latter.  
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Figure 4.1 The KP-32 is a good example of an advanced user station (keypanel).  
GPI (or GPI/O) General Purpose Interface or General Purpose Input/Output. This refers to logical inputs  
and outputs that can be wired to external devices for various purposes (hence the term  
“General Purpose”). Typically, these are optically isolated logical inputs and relay outputs.  
However, other variations exist.  
Rack Unit(s) A standard unit of measure used when dealing with electronic equipment racks.  
(RU)  
1 RU = 1.75” (44.45 mm). For example: a particular piece of equipment is described as  
being 3 RU in height. This means that it is 5.25” (3 x 1.75”) in height. Detailed  
information on the specification of standard electronic equipment racks can be found in  
EIA RS-310**.  
**International Standard from Electronics Industry Alliance. See http:\\www.eia.org.  
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Figure 4.2 Example of Matrix Ports  
ADAM / ADAM-CS / ZEUS  
MATRIX  
Data  
1 - 8  
Data  
9 -16  
Data  
17 - 24  
1
2
3
4
1
2
3
4
Out 4  
In 4  
PORT #4  
Data 1 - 8  
Out 1  
In 1  
PORT #1  
Data 1 - 8  
History of Matrix Intercoms  
Properly, it can be said that matrix intercom systems go back to the advent of automated  
central office telephone switching systems in 1892. Matrix intercoms, even today, owe a  
great deal to the concepts and technologies of those systems.  
In the 1950s, McCurdy Radio Industries of Canada introduced the 7000 Series matrix  
intercom based on wire per crosspoint and reed relay technology. Its basic building block  
was a crosspoint card containing six crosspoints. It was the first known matrix intercom  
system developed for the broadcast industry. In the early 1970s, in a project for the CBC,  
a solid state crosspoint was developed and the resulting matrix intercom system was  
named, the 9100. This was still “wire per crosspoint” technology, but density increased to  
allow a 10 X 1 format on a single crosspoint card. A 10 X 10 system could be built in only  
7RU. The 9100 gradually kept expanding and graduated to the 9200 series. The largest  
system built was a 60-port system delivered to CBC Winnipeg.  
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In the late 1970’s, microprocessors became available and the first truly intelligent  
intercom system, the McCurdy 9400, was delivered. This was the first system that used  
data sent from the user stations as opposed to one wire per intercom key. As  
microprocessor technology improved, the 9400 was replaced by the 9500 series. This  
series was more dense, allowing a 50 X 50 system in 3RU. The technology was modern; a  
very conventional square array of switches allowing any input(s) to be switched to any  
output, but the implementation was somewhat limited by what is called the “square law”  
problem.  
Briefly, in traditional matrix technology, in communications, audio, and video routing  
systems, the size (electrical and physical) of a matrix is related to the number of inputs and  
outputs, or “ports”, in a mathematical “square law” relationship.  
Figure 4.3 A Comparison 3x3 vs. 9x9 Matrices  
3 X 3 Matrix  
with 32 (9) Crosspoints  
9 X 9 Matrix  
with 92 (81) Crosspoints  
1
X X X  
X X X  
X X X  
1
2
3
4
5
6
7
8
9
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
X X X X X X X X X  
2
3
1
2
3
1
2
3
4
5
6
7
8
9
If you examine Figure 4.3, you can see that the 3 x 3 matrix, which is needed to support a  
three-user intercom system, has nine crosspoints. The 9 x 9 matrix, for nine users has 81  
crosspoints, so by tripling the number of users, the size of the matrix has increased from 9  
to 81 crosspoints or nine times. As nine is equal to the threefold increase in number of  
ports squared, the term “square law” has come to represent the problem.  
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Table 4.1 Number of Users vs. Number of Crosspoints  
Number of Users  
Number of Crosspoints  
10  
100  
25  
625  
50  
2,500  
10,000  
40,000  
160,000  
100  
200  
400  
As you can see in Table 4.1, while a ten-user system “only” requires 100 crosspoints for  
all possible communications paths, a 100-user system requires 10,000 crosspoints. Now,  
realize the number of crosspoints has a direct correlation to power consumption, physical  
size, and cost. It becomes apparent that with a traditional architecture, crosspoint matrices  
have a pretty small limit on maximum practical size.  
When McCurdy Radio Industries introduced their 9500 series matrix intercom product, 50  
ports required a rack frame 3 RU in height, and weighed 20 pounds. At the time, the size  
limitation was understood, but not regarded as a problem because it was thought that no  
one would ever need more than 50 users in a single intercom matrix. Today, we can look  
back and put that statement in the same category as IBM’s assertion in the 1950’s that “the  
world market for computers is 5 systems – TOPS,” or the apocryphal Bill Gates quotation  
to the effect of, “Who will ever need more than 640K of memory?” In 1985, the market for  
systems as large as a 50-user intercom was primarily limited to the major television  
networks.  
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Figure 4.4 A comparison of the 9400 Intercom System to the 9500 Intercom System (see inset).  
The 9500 represented a tremendous reduction in physical size.  
By 1988, the limits of the square architecture were beginning to show. The 350 port  
McCurdy 9700 matrix intercom systems that NBC commissioned for the 1988 Seoul  
Olympics required 10 full racks, over 20 kW of power, and weighed in at over 2 tons. The  
9700 matrix was the largest matrix intercom of its day. While providing nearly all the  
features of today’s most advanced intercom systems, the limit on size had been reached for  
traditional architecture.  
By the early 1990s, manufacturers in Europe were developing intercoms based on a new  
architecture. Time Division Multiplexing (TDM) had been deployed in telephone routing  
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and switching systems much earlier, and now it would be applied to matrix intercom  
systems.  
In a TDM matrix, the incoming signals from users (microphones or headsets) are run  
through an A/D converter and assigned a “time slot” on a TDM backplane. A good  
(although not strictly accurate) analogy would be the signals on a cable TV system.  
Whereas on the cable system you might have ESPN, HBO, and MTV, on a TDM  
backplane you would have the timeslots for Director, Producer, and Camera1. A user can  
then listen (or be talked to by) any or all of the timeslots. Determining which signal is  
heard is under software control, and can (generally) be selected by the listener, or pre-  
programmed. It can also be a function in which other users are calling the listener at that  
moment.  
Figure 4.5 An example of how multiple signals are “time-sliced” for use in a TDM system.  
Again, if you use the cable TV analogy, it is easy to understand why the systems do not  
have to obey the square law. In a conventional square law matrix, adding a single user to a  
2
2
100-user matrix requires the addition of 201 crosspoints (101 -100 ). In the TDM world, it  
requires the addition of two simple bits – a “transmitter” for the already existent time slot,  
and a receiver to tune in the other time slots for that user to hear.  
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Figure 4.6 Conventional Matrix vs. TDM Matrix  
Today, nearly all matrix intercoms are based on TDM or similar technology. Telex  
manufactures the RTS™ Zeus™, ADAM™-CS and ADAM™ TDM Matrix intercoms,  
Clear-Com has the MatrixPlus3, and other manufacturers in Europe offer TDM-based  
solutions to their markets.  
Modern Day Matrix Intercoms  
As discussed in the last section, today’s matrix intercoms are TDM based. Let’s take a  
closer look at the architecture of such a system, as a prelude to understanding its exact  
capabilities  
As shown in Figure 4.6, one major difference between conventional crosspoint matrices  
and TDM matrices is that a TDM matrix is comprised not simply of crosspoints, but is a  
full-fledged audio mixer. The offshoot of this can be understood by the following  
example:  
In the conventional crosspoint matrix shown in Figure 4.6, if the TD wants to listen to both  
the Director and the Producer, then crosspoints A3 and B3 are turned on (or closed). As  
these crosspoints are nothing more than switches, the relative levels of the signals are  
wholly dependent on the speaking level of the Director and Producer.  
In the same example through the TDM matrix, the crosspoints are replaced by volume  
controls – the resulting matrix is referred to as having individual crosspoint level  
adjustments. In this case, the capability exists for the relative signals levels to be adjusted  
by volume controls for the Director and Producer as heard by the TD. Various means can  
be used to make that adjustment, but for now the salient point is that different listeners (or  
outputs) have the ability to selectively mix the signals from the sources they wish to listen  
to.  
For the most part, this is the major difference between conventional crosspoint intercom  
matrices and modern TDM (or similar technology) matrix intercoms. There are other  
differences that are primarily a function of the addition of features and capability which  
are part of the normal product development process. These details will be discussed in the  
next chapter when we get into system design issues.  
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Special Considerations  
When considering the type of intercom system to install for a given application, there are  
many factors to take into account and many of these have been discussed in an earlier  
chapter. These factors are discussed in detail in the following section on advantages and  
disadvantages of matrix intercom systems versus the other types of systems available.  
Advantages  
Matrix intercom systems have numerous advantages over other types of intercoms. These  
advantages include size, configurability, variety of communication types supported, and  
ancillary functions available. The following discussion will refer to the RTS™ ADAM™  
Intercom System, but a number of the principles may apply to other matrix intercom  
products.  
Size  
In this context, size refers to the number of user stations supported. The RTS™ ADAM™  
line of intercoms is available in sizes from eight users up to 1,000+ in a single matrix, and  
can be expanded by means of trunking to include 31 such matrices interconnected. A  
typical hardwire PL system is no more than four channels – although most modern PL  
systems can be expanded to a dozen or more, the economics and ergonomics quickly  
become less desirable with size.  
Configurability  
In a matrix intercom system, the hardware is typically installed once and not altered day-  
to-day to accommodate day-to-day operational needs. Since each user station has the  
electrical capability to be connected to any other user station (via the crosspoints or  
individual crosspoint adjustments), changing who talks to whom, rules for what happens  
under certain circumstances, and the assignments of keys are under software control. In  
matrix intercoms this configuration can be done in many ways. There is usually a  
computer connected to a port of the matrix with software that allows changes to be  
entered, activated, and saved. Additionally, changes the users are allowed to make on their  
panels can be used to configure the system.  
The flexibility to make these changes and more without the need for labor intensive wiring  
changes are a key advantage of matrix intercom systems. It allows a single system to  
function as three independent intercoms for three studios most of the year and as a single  
large system during election coverage by the simple act of loading a new file.  
Types of Communications Supported  
A modern matrix intercom system has the ability to allow any of the user stations to be  
connected to any of the other stations. Since the connections are under software control,  
virtually any communications configuration can be accomplished, and as such, there are  
very few limitations on type of communications supported, without the need for  
specialized hardware.  
A great deal of the capabilities of modern matrix intercom systems is in the ease of which  
they allow different types of communications to be established. For example, from your  
home telephone you can establish a four-way conference call. It may involve calls to the  
operator, or conferencing in two people, one of whom then conferences in a third, but it  
can be done. At the office, it may be a bit easier. Call Alice, press the “CONF” button on  
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your telephone; Call Bill, press the “Conf” button again; call Chuck, then press the  
“CONF button, and you have a conference with all parties involved. With a matrix  
intercom system, you press the talk keys assigned to Alice, Bill and Chuck and say “Meet  
me on Tech PL”. You, Alice, Bill and Chuck each press “Tech PL” on your user station,  
and instant conference.  
Other types of specialized communications can be established as easily (or easier) in a  
matrix intercom system. These types include the following:  
Conference or PL – described above  
Isolate or ISO – a temporary private discussion amongst two parties  
IFB – Temporary interruption of a program signal with private conversation  
Special List or Group Call – Single key to address many individual users (also used as  
“All Call”  
Telephone – single key to answer an incoming telephone call, or to make an outgoing  
telephone call (requires telephone interface, such as RTS™ TIF-2000).  
Relay – pressing a given key activates a relay – a typical use would be to activate a  
transmitter to send audio communications via wireless.  
Ancillary Functions  
Warning! Low-key sales pitch …most modern matrices provide some form of ancillary functions. I  
will describe those which are common to the matrices I have experience with, including  
competitors of Telex, then I will delve into some functions which I know to be available in  
the RTS™ line of Matrices including Zeus™, ADAM™, and ADAM™-CS intercom  
systems.  
The most common ancillary functions are those referred to under the heading of interfaces  
or “GPI/O.” Quite often, in an intercom system, there is a need to interface to varying  
degrees with the outside world, and the more complex the intercom system, the greater  
need for such interfaces. Usually, these methods are quite predictable and the  
manufacturers provide or recommend a solution. A good example is a telephone interface  
that allows the intercom system to tie to the public telephone system to allow users to “dial  
in” or be called by the intercom system.  
Basic Ancillary Functions via GPI/O General Purpose Input / Output  
Oftentimes the interface needed is not so predictable, a user may have a need for the  
intercom system to flash a strobe light when calling into a high noise environment or to  
activate a “gong” signal over a paging system to announce a message. For these purposes,  
relays (one form of the “O” in GPI/O, which means “output”) can be wired from the  
intercom system to the strobe or gong generator and programmed to activate when  
required. Relays are not the only form of output available. A given system might instead  
provide a logic level signal or an open collector signal from a transistor or opto-isolator.  
The opposite need might also arise. A need for a signal, external to the matrix system, to  
cause the intercom system to undertake a certain action. As defined previously, a user  
station is a device that feeds a “port” of the matrix intercom system. At its most basic, it is  
a “box” with three basic functions. First, it takes speech through a microphone, amplifies,  
and processes it to a given signal format (balanced +8 dBu audio in RTS™ Matrices) to  
feed the matrix. Second, it takes audio signals from the matrix (again. +8 dBu in RTS™  
matrices) and converts them to a level suitable for driving a speaker. And third, it provides  
some degree of signaling and control to the matrix. For example, something which says to  
the matrix, “the user wishes to send his (or her) voice to FRED.”  
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Figure 4.7 Typical Keypanel  
Typical User Station  
(Keypanel)  
+ 8 dBu Audio  
From Matrix  
(Listen)  
Speaker  
Rs485 Data  
To Matrix  
Serial  
Data  
CPU  
Headset  
Switches  
Indicators  
Microphone  
+ 8 dBu Audio  
To Matrix  
(Talk)  
Normally, a user station provided by the manufacturer of the intercom performs all of  
these functions. However, suppose the user requires a user station to be very small, low  
cost, and mounted in a single gang electrical box, and that the station only needs to call a  
security desk. The user, dealer, system contractor, or any third party company can build a  
small box with a microphone, preamplifier, audio amplifier, speaker, and a push button.  
The only question is, how does the builder easily create the control protocol to notify the  
matrix that he or she wishes to be heard? Making the situation more difficult is the fact that  
manufacturers do not publish the details of their control protocols.  
The answer is simple. The push button of the user station is connected to a logic input of  
the matrix (the “I” in GPI/O) and the operating software is instructed to treat the activation  
of that logic input as the press of a talk key pre-assigned to the security desk.  
Figure 4.8 Simplified Low-Cost User Station  
Single Gang  
Electrical Box  
“Vertical”  
Simple One Button User Station  
Microphone  
+ 8 dBu Audio  
To Matrix  
Speaker  
CALL  
Switch  
+ 8 dBu Audio  
From Matrix  
Contact Closure to  
Matrix GPI Input  
MIC  
Speaker  
CALL  
A number of other examples with more detail of GPI/O are shown in the next chapter.  
More Complex Ancillary Functions  
The examples above presume that the interface requirements are very basic, and can be  
defined as an action which controls or is controlled by a single change in one logical state,  
a single “bit” of binary information.  
There are often cases where the definition is nearly as easy, but multiple conditions must  
be met. Perhaps, in the previous security desk example, the user needs a certain intercom  
panel to call the receptionist from 8:30 AM until 4:30 PM, then from 4:30 PM until  
midnight calls the security desk, and then from Midnight to 8:30 AM sends the signal  
through the building paging system to wake up the watchman.  
Another example, if the “ON AIR” light in studio three is on, DO NOT allow audio to go  
to the three speaker stations in studio three, unless the panels are feeding headsets AND  
NOT the built in speakers.  
In RTS™ Zeus™, ADAM™-CS and ADAM™ matrices there is a feature called User  
Programmable Language (UPL), which allows the following conditions to be tested:  
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Output from a Previous UPL Statement  
GPI Input  
Local GPI Input  
Status of a GPI Output  
Status of a Local GPI Output  
Talk Key Status  
Listen Key Status  
UPL Resource  
Crosspoint Status  
Input Talking  
Output Listening  
Headset Transfer Switch Status  
Current Date  
Current Time  
IFB Interrupted  
Counter  
This allows the test to be chained with other conditions via AND, OR, NOT and XOR to  
be tested and cause one of the following (or multiple of the following) actions to take  
place:  
Close Crosspoint  
Inhibit Crosspoint  
Assert GPI Output  
Inhibit GPI Output  
Assert GPI Output Local  
Inhibit GPI Output Local  
Force Talk Key Closed  
Force Talk Key Open  
Dim Crosspoint Volume  
Load Setup File  
Force Listen Key Closed  
Force Listen Key Open  
Clear Counter  
The user can construct these statements easily using selections chosen from pull down  
menus in the operating software. UPL is the answer to the time dependent routing  
described above.  
Getting more difficult, there are cases where the possible actions and situations are much  
more complex, and an external computer or device of some type is involved.  
An example of this is a large television complex where an automation or scheduling  
system assigns a given control room to a given studio. The routing switches, camera tally  
matrices, machine control, and intercom systems are expected to make appropriate  
assignments in support of that configuration.  
Another example might be a group of conference rooms that can be combined or used  
individually as controlled by a system such as manufactured by Panja (AMX) or Crestron.  
Again, the intercom system must respond to these assignments from the external systems.  
For this need, RTS™ has implemented a serial RS-232 control language called  
“Command Line Protocol” which is standard on the Zeus™, ADAM™-CS and ADAM™  
matrices. This protocol allows simple ASCII communications between the intercom  
matrix and the external computer. The protocol is published, and is contained on the  
accompanied CD. A typical statement might look like this:  
To accomplish the following:  
Force the following crosspoints:  
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input 1 --> outputs 43, 44, 45  
input 3 --> output 43  
program input 1 --> output 45  
also inhibit the following crosspoints:  
program input 1 --> output 1  
Issue the following ASCII Command String to the Matrix:  
IN1FI43F44F45F1IIN3FI43FINPG1FI45F  
The simplified ASCII command line protocol still requires some programming to take  
place external to the matrix to either translate the native language of the external control  
®
system to Telex Command Line Protocol, or to modify the internal code of the third  
party device to speak and understand Command Line Protocol. This effort is likely small  
when compared to the benefits of such tightly integrated control between systems. Now  
that we have outlined the advantages of matrix intercom systems over other types of  
systems, let’s go to the opposing viewpoint.  
Disadvantages  
Matrix intercom’s disadvantages over other types are pretty much the opposite of the  
advantages listed above. Disadvantages include size, cost and complexity. Complexity, in  
particular, renders them unsuitable for many applications.  
Size  
Here, size refers to not only the number of ports, but physical size as well. The smallest  
physical matrix available today is the Zeus™ matrix that is two RU in height. Add in a  
single RU user station and you now have a minimum of three RU of rack space required.  
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By contrast, Telex RTS™, AudioCom , and RadioCom™ intercom systems (as well  
as some competitors) offer systems providing both a multi-channel user station and a  
system power supply in a single RU. Matrices with larger number of ports become  
correspondingly larger, physically. There are times when size is of paramount concern  
such as, travel packages for news crews, remote trucks, cockpits, and Manhattan.  
True Story! One customer in NYC justified replacing their 15 year old matrix intercom with a newer  
system solely on the space and power savings (electricity and cooling), going from more  
than 18 racks to 2 racks of equipment and increased the number of ports in the process!  
Cost  
Again, somewhat related to size. If the intercom needs are small, and the complexity of  
requirements are not great, the overhead of having the matrix is hard to overcome. As an  
example, (2001 pricing) an intercom system with four users communicating over two  
channels can be completely for less than $1,600, using a party-line system. Given the  
relatively high cost of any matrix, four user stations along with a matrix would cost at least  
$8,000. The matrix system would have tremendous expansion and many extra features, but  
if that is not required, the cost is a definite negative factor.  
Complexity  
Complexity is quite often the major negative to matrix intercom systems. Complexity  
brings a whole world of issues, which can be of major consequence. I’ll start with a few  
examples based on our “friend” the personal computer.  
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You are in your kitchen – QUICK, multiply 347.2 times 15.8 –  
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Well let’s see, I could go down to the den, turn on the computer, wait for Windows to  
boot up (have a cup of coffee), start my spreadsheet program, and type in  
“=347.2*15.8<enter>,” read the answer – “oops, no pencil -%(&#@) Select File, Page  
Setup, Set Print Area highlight the cell with the answer, Print, wait for the Laser Printer  
to warm up, take the print out, tell the computer to shut down, go back upstairs….” elapsed  
time 9 minutes.  
— OR —  
Take the free Time Magazine calculator out of the junk drawer in the kitchen and press  
347.2 X 15.8 = and read the answer (5,485.76 for you curious types).  
Same example, except now you are not in your home but in a research lab you are visiting,  
and see a pocket calculator lying next to a turned off monitor for a workstation. Now the  
considerations become more complex – does the workstation work at all? Is it an operating  
system I understand? Does it have a spreadsheet program at all? Would turning the  
monitor on and trying to start a spreadsheet disrupt some important research? Which  
device would you choose to get the answer?  
Last example – you are not computer literate, the only PC in the house belongs to the  
expert (your 12 year old daughter and she is at a neighbor’s working on the web site for  
their dot.com startup). “Oh, for gosh sakes, just hand me the calculator already!”  
Despite the attempted humor, the same considerations apply to matrix versus TW or  
wireless intercom systems. Matrix systems (like PCs) are good for complex things, and  
they can also do simple things, but if PCs really were good for the small jobs, why do you  
still have that calculator, pencil, pad of paper, photocopier, and fax machine in your  
office? The answer is because, like with an intercom system, sometimes all you need to do  
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is to scribble “call Paul” on a Post-it note to put on your computer monitor for after  
lunch.  
TW and wireless intercom systems are generally simple to operate, transport, hookup  
(configure), and do not require an expert to setup. This is especially true if the system in  
question does not need to change on an hour-to-hour or day-to-day basis. They are very  
affordable, robust, reliable, and physically small.  
Interconnection between components may be a simple as thin air (wireless), microphone  
cable (PL), coax or twisted pair for matrix, but is more likely to be multi-conductor cable.  
Again, another layer of complexity.  
To change the configuration of a PL system, you can likely just change which units are  
tied together by changing cables, or by turning some switches on an assignment panel. In a  
matrix system, you will likely need to connect a PC and run the configuration program.  
Figure 4.9 Use of Source Assignment Panels such as this SAP-1626 allow the rapid  
reconfiguration of PL systems without changing any cables  
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So now…Quick! You need to setup an intercom on the roof of your facility to cover a  
local parade. You can go to your matrix intercom, locate two unused ports, assemble  
appropriate length three pair cables, fish the cables up to the roof. Then fish a power cord  
to the roof, take two keypanels up there (hope it’s not raining), and connect the panels.  
Now go down to the configuration PC, assign appropriate keys to those panels. Go back to  
the roof and verify that you have communications. – “What do you mean the parade ended  
two hours ago?”  
— OR —  
You can take two beltpacks and two microphone cables to the roof, daisy chain the  
beltpacks together, drop the single microphone cable down to the equipment room and  
either connect directly to your existing PL system or to the interface between your PL  
system and the matrix for (nearly) instant communications. Do the same example using  
wireless intercom, and it gets even easier!  
For all the strength, features, and power of modern matrix intercom systems, there are  
many situations where they are more of a burden than a solution.  
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C H A P T E R  
5
C
HAPTER 5  
DESIGN OF MATRIX  
INTERCOM SYSTEMS  
RALPH STRADER  
Introduction  
In this chapter, we will address the major issues and considerations for designing a matrix  
intercom system. At the end of the chapter, you will not know everything to specify, plan,  
design, and install a matrix intercom system. Nevertheless, you will have a good idea of  
the basic requirements, pitfalls, and opportunities involved in the design and installation of  
a matrix intercom system.  
Back-to-Basics  
As discussed previously, a modern matrix intercom system is very similar to a telephone  
system. It is comprised of, in its most basic form, a Central office switch (the matrix),  
interconnect wiring, and telephones (user stations). Most of the concepts and some of the  
terminology is common to both. Calls can be made, busy signals encountered, “call  
waiting” exists, conference calling is possible, unlisted numbers can exist, calls can be  
blocked (incoming and outgoing), and long distance (trunking) is possible.  
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The following examples will use the Telex RTS™ ADAM™ intercom matrix, unless  
otherwise noted. Most matrices on the market today will have similar features, but unlike  
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Telex products, the competitors’ units are not designed to also prevent dandruff, solve  
the meaning of life, the universe and everything (with apologies to Douglas Adams), and  
achieve world peace. We would like you to believe that our products will do so. (And in  
writing that I felt a bit like Dogbert from Dilbert.)  
RTS™ Matrix Intercom Systems  
Because of design and installation issues specific to the brand of intercom matrix used, it is  
now necessary to talk in some detail about the specifics of the RTS™ products, including  
Zeus™, ADAM™-CS and ADAM™ intercom matrices, as well as some accessories.  
When I refer to the ADAM™ series of intercoms in the following portions of the chapter,  
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unless otherwise noted, the comments also apply to ADAM™-CS and Zeus™ intercom  
systems.  
Previously, we discussed the analogy between telephone systems and matrix intercom  
systems – the analogy is not correct in all cases, here are some exceptions.  
Figure 5.1 Typical ADAM™ Matrix Connections  
In ADAM™ matrix intercom systems, the connection between the matrix and keypanel is  
normally via three twisted pairs of unshielded cable. As shown in Figure 5.1, one pair  
carries balanced audio from the keypanel to the matrix, one pair does audio in the opposite  
direction, and one pair is a RS-485 data signal which is shared among 8 panels in a group.  
IMPORTANT As eight panels share one physical data line, the matrix must have some means of  
identifying which panel is sending data to it, and also have some means of addressing  
messages to one specific panel of the eight. The key word in the previous sentence is  
“addressing.” Each keypanel in the system must be assigned an address by one means or  
another. On some keypanels this involves setting “dip switches” to select a “one of eight  
address” via binary code (KP-9x family of panels). On other keypanels, the address is set  
via rotary switch on the keypanel (KP-32 and Low Cost Series of Panels). And, on others  
the means is via menus and firmware (KP-12 series of panels). In all cases, the factory set  
default address has one chance in eight of being set correctly “out of the box.”  
If a separate keypanel is attached to each of the 8 ports which share a data line, each panel  
must have a unique address set which matches the physical port to which the panel is  
connected. Having a panel with an address different from the physical port to which it is  
connected will render that panel unusable (in a practical sense, even though the panel may  
receive audio). Having two or more panels in a given group of 8 with the same address  
will disrupt all eight panels in that group by causing data collisions on the common data  
line. This is so important that I will repeat it. Having two or more panels in a given group  
of eight with the same address will disrupt all eight panels in that group by causing data  
collisions on the common data line.  
At time of initial installation, or system modification, the great majority of anomalies can  
be traced to improper addressing.  
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As received “out of the box,” a matrix intercom system needs to be configured  
(programmed). This can include how many users are connected, how many conferences  
are expected, what you wish to name the users, who can talk to whom, and, just as  
importantly, who cannot talk to whom. In some cases, the default configuration upon first  
operation is adequate and may allow enough communications to meet your needs, but it is  
unlikely, and frankly, a tremendous waste of capabilities. We will discuss configuration  
via software in more detail later.  
In this chapter, we will first touch on the design and requirements aspects of the matrix  
intercom system, then move into installation, and finally operation. On the CD, we have  
included a full, up-to-date (as of this writing) AZ™-EDIT configuration software package  
which can be installed and ran on your PC. You do not need to have an intercom system  
connected to run the software.  
Note You may not be able to see and/or use some features because they require that an actual  
intercom system be connected to your PC.  
Loading and running the supplied software will add a good amount of “hands on” to your  
experience, but in the interest of keeping this book a useful reference, regardless of what  
intercom matrix system you may be exposed to, the examples given will not be specific to  
the included RTS™ AZ™-EDIT configuration software except where absolutely  
necessary.  
To Begin  
The first question you should ask, as with all systems design is, “What are you trying to  
accomplish?” The matrix intercom needed by a small station in Botswana (to avoid  
offending any US residents of small states who are no doubt tired of being referred to as  
being suitable for simple, basic, limited products) is considerably different from that  
required by MegaMedia Corporate Conglomerate Entertainment Enterprises Ltd. with 87  
stations, 4 film studios, and a theme park, located on 3 different continents, all engaging in  
joint productions.  
I find that system design is best started from the bottom up, rather than the top down. On  
that note, figuring the requirements for communications to determine the size of matrix  
needed and then later deal with informed compromises to meet size or budget  
requirements.  
I will also proceed on the basis that any needs for non-matrix portions of the system will  
be covered in detail elsewhere in the book, and that we need only concern ourselves with  
how to interface to them from the matrix.  
In this section I use a lot of examples which are television based, owing to my background  
in television, and the origins of modern matrix intercoms, which have been predominantly  
TV station driven. The questions and procedures are, however, relevant for all  
applications, regardless of industry.  
Let’s get started.  
How many individual locations and/or persons need to communicate with one another?  
Write them down. Organize them by logical grouping or location such as:  
Studio A  
Floor  
Lighting Director  
Camera 1  
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Camera 2  
Camera 3  
Floor Director  
TelePrompTer  
Anchor A  
Anchor B  
Anchor C  
Weather  
Control Room  
Director  
Producer  
TD  
PA 1  
PA 2  
Segment Producer  
Audio Operator  
News Computer Operator  
Font Operator  
Other  
Green Room  
Makeup  
Do this for all locations; it will give you a quick “port count” for your system, which will  
have a significant impact on size of the matrix, and, as a result, the cost. I presume that  
even if you do work for MegaMedia Corporate Conglomerate Entertainment Enterprises  
Ltd., you do not have an unlimited budget (Shame, really).  
Next, figure out what external “stuff” you need to deal with, such as:  
• Interface to allow access to telephone lines – How many? How capable?  
• Interface to TW (party-line) intercom systems.  
• Relays and GPI/O for external devices.  
• Interface(s) for remote locations such as:  
Transmitter.  
News Bureaus in other cities.  
ENG vans.  
• Interface to other matrix intercom system (trunking).  
Now, it is time to put some detail on the above requirements. For each identified user, you  
need to know certain things, such as:  
• How many other users will he (or she) need to readily communicate with at one  
“sitting” – this will determine the number of keys required on the keypanel.  
• Does the identity of the key assignments change? If not, a keypanel without displays,  
which relies on labeling strips, will save money.  
• Does the user want, need, or deserve the ability to reprogram their keypanel features,  
key assignments and defaults? If yes, a more complex panel may be required, and  
chance for errors is increased, but the user can make changes without involving you or  
some other expert.  
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• Does the user regularly need the ability to adjust individual volumes of the keys (not to  
be confused with the overall volume control which all panels have)? If yes, a Level  
Control Panel should be added to their station.  
• Is space an issue? Can a smaller panel be chosen which meets the other requirements?  
• Does the user really just need to be part of a given conference at all times? If yes, then  
putting that user and the other members of that conference on a TW channel and  
interfacing that channel to the matrix may make more sense.  
• Does the user need to be untethered? If yes, a wireless beltpack is required.  
• Is the user really “two-way”, or are they listen only – such as the paging speaker in the  
green room, or the earpiece (IFB) for the talent.  
• Is the user of sufficient stature that they will get “the top of the line” regardless? Those  
of you that have done systems design before have likely encountered this phenomenon.  
Those of you who haven’t encountered this previously would do well to ask yourself if  
the CEO of MegaMedia Corporate Conglomerate Entertainment Enterprises Ltd. really  
needs that Pentium VIII 35 GHz computer with the 30 inch monitor on his or her desk  
just to read weekly reports from the boys in marketing – The answer will enlighten you.  
In undertaking this exercise, it helps to have a catalog of available products (see Figure  
5.2) from your vendor of choice in front of you to assist you in categorizing which panels  
you will assume are suited for the intended user. A copy of the current (as of the  
publication date of this edition) RTS™ Matrix catalog, as well as the RadioCom™,  
AudioCom®, and RTS™ TW catalogs are on the included CD.  
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Figure 5.2 A wide variety of keypanel options exist. Here we have a selection of RTS™  
keypanels that fit a range of needs. Small keypanels such as the (A) KP-12LK and (B)  
WKP-4 provide an interface for those with limited keypanel needs. The (G) KP-96-7, a  
medium sized unit, was the workhorse of the RTS™ keypanel line until the 1980’s and  
1990’s. The (C) KP-32 is the top of the line keypanel, and can be enhanced through  
additional options, such as the (D) EKP-32 expansion panel, and the (F) LCP-32/16  
level control panel. The  
(E) KP-8T is an example of a specialty keypanel that makes use of an empty bay in a  
Tektronix vectorscope.  
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Let’s proceed on the basis that you have now compiled a list of needed equipment, have  
gotten approvals, placed the order, and are now ready to begin the installation of your  
system.  
Cable Considerations  
Cabling types do vary considerably among the manufacturers of matrix intercom products,  
as do the signals transported by them. For that reason, the following discussion is  
somewhat specific to RTS™ Zeus™, ADAM™-CS and ADAM™ matrix intercom  
systems.  
As noted earlier, RTS™ Matrix Intercom Systems typically use three twisted pair,  
unshielded cabling for interconnection. I use the word “typically,” as coaxial cable  
adapters are available from Telex to allow keypanels to be connected via coax, but the  
standard twisted pair methodology is more cost effective in most cases.  
Telex allows the user to choose from two different connector styles for the three pair  
connection. The choice is simply a matter of preference by the user. RJ-12 connectors can  
be used, and these are readily available, low cost, and quick to assemble.  
Note RJ-12 connectors are sometimes incorrectly referred to as RJ-11 connectors. While they  
are basically the same size, RJ-11 connectors have four conductors and RJ-12 connectors  
have six conductors.  
On the negative side, they are plastic, and not as robust as some installations demand. DB-  
9 (actually DE-9, the more proper name) connectors are also provided, and can be used.  
®
These will be more robust, but are also harder to wire, and more expensive. All Telex  
keypanels have both types of style connectors on them. The type of connector on the  
ADAM™ and ADAM™-CS matrices must be specified at the time of order, and can be  
either the RJ-12 or the DE-9 style. Zeus comes with DE-9 only.  
Figure 5.3 ADAM™ (including ADAM™ CS and Zeus™) Intercom Cable Connections  
CONTACTS  
DE-9P (MALE)  
TO KEYPANEL  
DE-9S (FEMALE)  
TO INTERCOM SYSTEM*  
Use AMP Chordal  
Crimp Tool 231648-1  
or equivalent  
123456  
RJ12 MODULAR PLUG  
AMP 5-555042-3 or equivalent  
(View from cable entrance)  
+
1
1
2
6
LATCH  
DATA  
-
2
6
+
-
4
4
5
9
AUDIO TO MATRIX  
3 TWISTED PAIR TELEPHONE CABLE  
5
9
PAIR 1: AUDIO TO MATRIX  
PAIR 2: AUDIO FROM MATRIX  
PAIR 3: DATA  
-
+
7
7
DATA -  
AUDIO FROM MATRIX  
1
1
8
3
8
3
AUDIO FROM MATRIX +  
2
3
2
CABLE TYPE:  
BELDEN 8777  
AUDIO TO MATRIX +  
3
AUDIO TO MATRIX -  
4
5
4
IMPORTANT!  
AUDIO FROM MATRIX -  
5
When connecting to an ADAM CS back panel, use  
only low-profile cable connectors such as AMP  
Part No. 747516-3 (Telex Part No. 59926-678)  
*
DATA +  
6
6
As seen in Figure 5.3, the wiring takes pin 1 to pin 1, pin 2 to pin 2, and so on, for both  
style connectors. What the drawing also shows, and is equally important, is that a given  
twisted pair cable carries both portions of the same signal. If you were to wire pin 1 to pin  
1, and pin 2 to pin 2, etc., but had one of the wires in a twisted pair carrying +audio in, and  
the other wire of that pair carrying -data, the audio would be degraded by having “data  
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buzz” audible in that audio signal. The data signal would not carry for as great of  
distances. This type of error is second in the top ten of initial installation problems, after  
addressing mistakes.  
ADAM™ and ADAM™-CS systems are also available with other wiring schemes,  
including multi-pin breakout to jackfields for monitoring and rapid changes and for use of  
25 pair “Telco cable” for distribution. More information on this can be found in the  
ADAM™ and ADAM™-CS System Installation manuals on the included CD.  
Audio and Data Considerations  
One of the benefits of the signal format described above is that generally, it does not  
matter how the audio and data signals get from the keypanel to the matrix. If you want to  
have a keypanel used in a Broadcast booth at the top of a football stadium which then is  
connected to an ADAM™ matrix in the Sports Truck below, it is perfectly OK to have  
prewired a small adapter to let you transport the three balanced signals (audio in, audio  
out, and data) over three microphone cables in the audio harness which is already run  
between the locations.  
Also, if you want to “piggyback” the audio and data on an existing corporate WAN  
running between two buildings on a campus, there should be no problem. The maker of  
your WAN hardware, no doubt, has modules available for your system that let you feed  
the balanced audio and data into an adapter that create appropriate format data to be  
merged into the WAN data stream, thus, you have eliminated the need to install any  
cables!  
If you have “dark fiber” available to you, Telecast Fiber and others make adapters which  
can take the audio and data, and run them down the fiber, even while running other audio,  
video and data down the same fiber for other purposes.  
Need to be able to “dial in” with a keypanel from a remote location to a matrix  
somewhere? Multi-Tech and other modem manufacturers make voice over data modems  
that can do the job. Intraplex and others make equipment that can take the voice and data  
signals and send them via ISDN or switched 56.  
Do both locations have bi-directional radio equipment? For example, satellite uplinks and  
downlinks, microwave studio-transmitter links (STLs), or wideband full duplex two-way  
radios. These will also work with appropriate modulators.  
Again, with one possible concern, which is discussed in the next section, it does not matter  
how you get the signals between keypanel and the matrix, simply that you do.  
Polling Issues  
Earlier, I mentioned one area of possible concern. In the examples I gave, where the  
distance between matrix and keypanels is large, the transit time can become problematic.  
If the distance is great enough, even the speed of light becomes a limiting factor.  
Geo-synchronous satellites are 22,000 miles above the earth. To send a signal up to one,  
and back down again will take on the order of a quarter of a second. To complete a round  
trip will take half of a second (500 milliseconds), at best. You may have heard this  
phenomenon on international telephone calls with your own voice coming back to you  
greatly delayed. While the voice delay can be distracting, the delays in data are the real  
problem. These data delays can become a problem even when the distance between the  
matrix and keypanel is “only” 3,000 miles – because the encoders, modems, muxes, etc. in  
that path also add delay; 30 milliseconds is typical.  
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We talked earlier about how addressing of keypanels is critical in the matrix intercom  
system. The way in which addresses work is as follows:  
In a given group of 8 panels sharing a common data line, the data gets sent from a  
keypanel to and from a matrix by a process called polling. The matrix will broadcast a  
signal to all eight panels to the effect of “Panel Number 1, do you have any changes for me  
to act upon?” These changes could be as simple as a talk key having been pressed or as  
complex as the user wanting to see a list of all available party-lines. The matrix expects an  
answer from the panel, either a simple “nope, nothing new to report” or a request for a  
specific action.  
The matrix normally will not wait very long (less than 10 milliseconds) for an answer  
before deciding that the panel in question is not there, and moving onto panel number 2,  
and so on, up to panel 8, and then starting all over again at panel number 1. The short wait  
is mandated in order to assure quick response to panel requests. This 10 milliseconds is the  
“polling window”, the 30 milliseconds between LA and NYC is the “polling delay”.  
To make such a system work without unduly slowing down all panels by globally  
increasing the system polling delay, you can use the AZ™-EDIT configuration software  
to allow a longer poll delay (say 33 milliseconds) for one panel with no appreciable impact  
on other panels.  
In the case of 250+ milliseconds delay due to satellite transit time, it is common practice to  
make sure the keypanel associated with the delay is in a group of eight ports where the  
delay is not important. For example, on ports that are used for paging outputs or IFBs,  
where there is no other data present.  
In these ways, remote keypanels become very manageable and feasible, due in large part  
to their common format of standard balanced audio and RS-485 data.  
Very Large Systems, Split Operation and Trunking  
We have used the term trunking earlier and likened it to the long distance telephone  
system. In the case of RTS™ ADAM™ matrix intercom systems, that analogy is very  
close to reality. Before we get deeply into trunking, let’s discuss the different ways  
available to make large systems.  
First, exactly what do we mean by a large system? How big is “BIG?” As we discussed  
earlier, with older technology (pre-TDM), systems were limited to a certain size (as a  
practical matter, in the “few” hundreds of ports) because of physical size and cost, not  
because of technological or logistic limitations.  
Today, intercom matrices in general, and RTS™ intercom matrices in particular, have a  
higher absolute limit, and a larger “typical size”. For example, in the early 1980s, a well  
appointed high end Sports Truck, the type which would do an NFL game, likely had 12 or  
so channels of PL, 6 IFB channels and 6 ISO channels. Today, most “network size” trucks  
carry 64+ ports of ADAM™ matrix, and in some cases, over 100 ports. The intercoms  
have grown to carry program audio for monitoring, support 10, 15, or 20+ cameras, a host  
of graphics operators, and statistics personnel. Clearly, what is typical today was  
unimaginable less than 20 years ago.  
Let’s consider matrix sizes for a moment, again sticking to those I know best:  
RTS™ Zeus™ Matrix Intercom System: 24 ports fixed.  
RTS™ ADAM™-CS Matrix Intercom System: 8 – 64 ports in groups of 8.  
RTS™ ADAM™ Matrix Intercom Single Frame: 8 – 136 ports in groups of 8.  
RTS™ ADAM™ Matrix Intercom Multiple Frames: 136 – 1,000 ports in groups of 8.  
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Figure 5.4 A Comparison of Relative System Sizes  
These are the numbers of ports that are available in a single RTS™ intercom matrix from  
Telex. Other manufacturers offer systems in sizes from eight to approximately 500 ports.  
As you can see, size is not a limitation in most cases. At the time of this writing, the largest  
known single matrix intercom system in service is a RTS™ ADAM™ system which  
consists of 784 ports at both ESPN and NBC.  
Size and capability are not the limiting factor in most cases. Many factors may guide the  
design in favor of smaller individual systems. If the system is needed for four separate  
studios in a facility, which never or very rarely work together, then it may make more  
sense to use four separate systems. Some very good reasons for doing this might include:  
Cost: Four 128-port systems cost less than one 512-port system.  
Reliability: A fire in one rack room will not destroy the entire system.  
Manageability: Four different control studios have four different crews affecting the  
setup of their operation.  
Shorter cable runs: The matrix for a given group of panels can be physically closer to  
those panels.  
Ease of Expansion: It is easier to expand a single matrix if the needs for one area grow.  
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Now, let’s take the opposite tack; what would be the reasons for going to a single large  
matrix? Some of the reasons might include:  
• Operations require ability for any of the 512 users to communicate with any of the other  
users.  
• Desire for single point of administration, control, troubleshooting and monitoring.  
• Design of the facility is highly decentralized operationally, and day to day, different  
portions of the facility must work together.  
• Certain users must work with all the facilities, and giving them four separate keypanels  
(one per system) is not feasible.  
Now we have helped to identify whether to use one large matrix or a number of smaller  
ones. What happens when you get mixed answers to the questions above? Certain  
requirements drive you to use separate matrices, but one or two key factors seem to  
demand a single matrix.  
A couple of different options or “hybrid designs” can be used in these cases.  
The first and simplest is to define a few common points of contact between the intercom  
matrices. Take the following example, a television complex has two studios and two  
control rooms. Normally Control A works with Studio A, and Control B with Studio B.  
Occasionally, the wall between the two studios opens, (never mind how; that’s the  
architects problem!) and there is a need for Control A to work with the cameras in the  
combined Studio AB.  
Let’s further presume the normal method of operation has the cameras in each studio  
receiving two channels of intercom; a “Technical PL” created in the intercom  
configuration, and a “Production PL” also created in the intercom configuration of the  
respective matrices for Studio A and Studio B.  
Figure 5.5 Separate Studios, Separate Intercom  
INDEPENDENT MATRICES IN 2 STUDIOS  
STUDIO B  
STUDIO A  
= Production PL Studio B  
X
= Production PL Studio A  
X
= Technical PL Studio B  
X
= Technical PL Studio A  
X
Dir A  
TD A  
Dir B  
TD B  
X X X X X  
X
X X X X X  
X X X X X  
X X X X X  
X X X X X  
X
X X X X X  
X X X X X  
X X X X X  
X X  
X X  
PROD A  
CAM 1  
PROD B  
CAM 3  
CAM 4  
CAM 2  
VIDEO A  
PROD PL A  
TECH PL A  
VIDEO B  
X
X X  
X X X X X  
X X  
X
X X  
X X X X X  
X X  
PROD PL B  
TECH PL B  
X
X
A quick way of allowing the combined operation would be to configure (in AZ™-EDIT)  
the Production and Technical PLs of each matrix to include two available sets of ports on a  
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jackfield. Then, simply connect the output of Production PL from Studio A to the input of  
Production PL for Studio B, and conversely, connect the output of Production PL from  
Studio B to the input of Production PL for Studio A. Do the same for Technical PLs.  
Figure 5.6 Fixed Trunking  
Now, any conversations on Production PL for A control will also be available to the Studio  
B cameras for both talking and listening, and the same is true for the Technical PL. Our  
problem is solved.  
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The technique described is called trunking; the two ports of each system assigned to PLs  
have been “trunked” to one another. For reasons that will become clear later, we refer to  
this as “dumb” or unintelligent trunking. That isn’t to say that it isn’t a brilliant idea or  
solution. It means that no system intelligence was employed in establishing the trunks.  
To go back to our telephone system analogy, this is early-20th century technology,  
harkening back to the days of an operator in your hometown asking the long distance  
operator for a “trunk” to Chicago. That trunk then connected you to your Aunt in Chicago.  
But, “wait,” you say, “didn’t the telephone make this much easier back in the fifties by  
going to long distance area codes and direct distance dialing?” Yes, you are absolutely  
correct, give the reader a prize!  
Today, some intercom matrices (including at least one from someone other than Telex)  
offer varying degrees of improved trunking that eliminates the manual patching described  
above.  
WARNING Sales pitch coming – Telex has the largest, most intelligent, most proven trunking system  
available today, offering the ability to trunk more than 20 ADAM™, ADAM™-CS, or  
Zues II systems together.  
This can all be done without human intervention and in a system comparable to the long  
distance telephone system. Let’s look at some of the features and attributes of the system.  
Taking the example of the two Production and Technical party-lines manually trunked  
together given earlier, let’s make a couple small changes. Make the “trunking ports”  
assignable, and give them the designations “Trunk A” and “Trunk B,” Connect a  
“computerized operator” between the two systems, communicating via a standard RS-232  
serial port with both matrices. Let’s call the computerized operator the “Trunk Master.”  
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Figure 5.7 Intelligent Trunking  
INDEPENDENT MATRICES IN 2 STUDIOS  
with Telex Intelligent Trunking  
STUDIO A  
= Production PL Studio A  
TRUNK MASTER  
X
= Technical PL Studio A  
X
Dir A  
TD A  
Data  
“Computerized Operator”  
X X X X X  
X
X X  
PROD A  
CAM 1  
X X X X X  
X X X X X  
X X X X X  
CAM 2  
VIDEO A  
TRUNK 1  
TRUNK 2  
X
X X  
X X X X X  
X X  
X
STUDIO B  
= Production PL Studio B  
X
= Technical PL Studio B  
X
Dir B  
TD B  
Trunk Assignments Dynamically  
Allocated by Trunk Master  
X X X X X  
X
X X X X X  
X X X X X  
X X X X X  
X X  
PROD B  
CAM 3  
CAM 4  
VIDEO B  
TRUNK 1  
X
X X  
X X X X X  
X X  
TRUNK 2  
X
Now, all we need to do is assign “area codes” to identify which matrix has which port. In  
®
actuality, in the Telex Intelligent Trunking system, the trunk master figures out which  
matrix has which ports and keeps track of it for you. If you assign “ADIR” from the Studio  
A matrix to a panel on the Matrix for Control Room B, the system “knows” that it will  
have to configure and establish a trunk to allow that conversation to take place. It does so  
automatically, establishing the trunk, monitoring trunk usage, and releasing the trunk  
when the conversation is completed.  
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“Great” you say, “Why not always trunk and avoid HUGE matrices?” I’m glad you asked  
that question.  
First, there is what I refer to as the “Mother’s Day Syndrome.” Mother’s Day rolls around,  
and all good sons and daughters decide to call their dear, sweet mom and wish her the best,  
and many of them don’t get through. They hear a nice recording of someone saying, “All  
circuits are busy, please try your call again later.” If you think about it, you have probably  
gotten that message a few times in your life when calling long distance, and never when  
calling someone down the block. This is because local calls (large metropolitan areas  
excluded) go through a single matrix (single central office), and there is a dedicated  
crosspoint (or a close equivalent) for each path. You get the message when calling long  
distance because there are a limited, finite number of long distance trunks available, and  
the heavy traffic volume keeps all of them busy at times.  
Looking at the last example, imagine what would happen when the first person from  
Matrix A calls someone in Matrix B, Trunk A (or B) gets assigned, and life is good. A  
second person (maybe from B calling A this time) initiates a call, the other trunk is  
assigned and life is good. Now a third person in Matrix A decides to try to call someone in  
Matrix B. Oops, “All circuits are busy, please try your call again later.”  
In actuality, no voice is heard, but the calling party does get a busy indication on their  
panel, and the call does not go through. Therefore, we can see that trunking systems need  
to be sized appropriately for the anticipated traffic. Appropriately is the key. The  
Telephone Company (actually “companies” in the post-AT&T breakup era) set aside  
enough trunks to handle all of the traffic most of the time – sounds suspiciously like “You  
can fool all the people some of the time,” doesn’t it?  
®
Telex Intelligent Trunking shares something else in common with the telephone  
company, the trunk master continuously monitors and reports on status of trunk utilization.  
The telephone companies do it in great “war rooms” with multi-story maps with lighted  
paths. Telex does it with a constantly updated and logged report of trunk utilization on a  
conventional PC. It keeps track of (amongst other things) the maximum number of trunks  
you use simultaneously in the past x amount of time. With good historical data, you can  
determine the number of trunks you set aside for trunking.  
However clever you think you are in setting aside trunks, there will always exist the  
unforeseen possibility that you may run out of trunks at some point.  
For example, you have two studios, trunked together with five trunks, and in the past year  
have never used more than four at one time. Today, both studios are manned, and in Studio  
B is a news program being directed by Steven Spielberg, produced by George Lucas, with  
Tom Brokaw interviewing Madonna and Jerry Falwell (it could happen!). Studio A is busy  
doing a documentary on the history of dental appliances in South America. Care to take a  
guess how many of the crew in studio A will decide to listen in to the director, producer,  
talent IFB, program audio, cameras from B? All at the same time? Know what’ll happen?  
Yep, “All circuits are busy, please try your call again later.”  
The other significant limitation may be for each trunk you assign (which requires a port),  
you give up a port that be used for two keypanels (one at each matrix). Make your system  
too long distance “friendly” by allocating a lot of ports as trunks, and you either limit the  
number of keypanels on each matrix or spend more money to buy additional ports for each  
matrix.  
All of these limitations aside, trunking can be a very good solution for many applications.  
Trunking works best when limited numbers of trunks are required to support occasional  
usage. Trunking works very well when many matrices need to be interconnected. As noted  
®
earlier, Telex Intelligent Trunking can simultaneously handle automated routing between  
more than 30 matrices. A side benefit of such a multiple matrix trunked system is that the  
trunk master can figure out and establish trunk paths via multiple hops if needed due to  
trunk usage. If the trunks from Matrix A to B (see Figure 5.8) are all in use, the possibility  
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exists for the trunk master to route a signal from A to C and from C to B, thereby  
bypassing the bottleneck.  
Figure 5.8 Cascaded Trunking  
Another advantage of trunking is that there is no requirement for the individual matrices  
involved to be in close proximity. Systems, which are hundreds or even thousands of miles  
away, have been successfully trunked using techniques described earlier with respect to  
remote keypanels. Trunking is nearly identical to those situations, requiring the  
transmission of a single data signal and the appropriate number of audio signals.  
Note A series of articles written by Andy Morris and Ralph Strader, on trunking at NBC,  
appeared in Broadcast Engineering magazine in 1996. These articles, as well as an article  
on Trunking Supervisory Systems by Robert Streeter and Thom Drewke of NBC, in PDF  
format, are included on the CD.  
A final methodology for distributing large matrices is a function of the manner in which  
multiple ADAM™ frames are interconnected. When two ADAM™ frames, each 128  
ports, are connected together, they become a single 256-port intercom system. The  
interconnect between the two frames is through a Bus Expander, which transports all 128  
ports between the two frames without rendering any of them unusable for keypanels.  
The physical interconnect between the frames with bus expanders can either be via a pair  
of coaxial cables, which can be used for distances up to 1,000 feet, or via a pair of fiber  
optic cables, which can run for over 1,000 meters. The signal sent over the fiber or coax is  
a multiplexed data stream, running at approximately 220 megabits/second. Since this data  
rate is lower than the 270 megabit CCIR-601 serial digital video standard, many of the  
asynchronous devices that can transport serial digital video can be used for this signal to  
achieve even greater distances.  
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By using the Bus Expander with multiple ADAM™ frames, a single electrical matrix can  
be located floors or buildings apart within a complex, and yet function as a single large  
matrix.  
Now that we have discussed a number of different methods used to create large intercoms,  
and how to interconnect smaller intercoms into a single system, let’s move onto  
interfacing and accessories.  
Interfacing  
It is rare that an intercom system is an island unto itself. Communications has become such  
a pervasive need and set of technologies that it’s not a matter of IF you interconnect; it is  
more a matter of WHEN and HOW you interconnect.  
If you doubt this, consider that today in your home, you may have a cable modem  
connecting your PC to your cable TV system; you may have your PC answering your  
phone and taking messages with an embedded voice mail system. Soon, you may have  
your refrigerator talking to the local supermarket over the Internet, ordering tomatoes and  
milk.  
Some of the more common needs for interfacing, which are encountered when installing or  
modifying an intercom system are presented in this chapter.  
Signal Formats  
TW and Wireless systems often are tied to matrix intercom systems. A brief description of  
the signal formats of the various types of intercom systems are helpful.  
In any intercommunications (intercom) system, the “inter” refers to two-way  
communication. For the purposes of this discussion, we label one of the directions as  
“talk” and the other as “listen”. Obviously, either party in a conversation can be talking or  
listening at any time, or even at the same time. “Talk” or “Listen” is a matter of  
perspective. In a given two-way communication, what “talk” is to me is “listen” to you and  
vice versa. This is only a matter of semantics, as far as this discussion goes; what is key is  
both sides of the communications can be occurring simultaneously.  
In a matrix intercom system of the type that RTS manufactures, the talk and listen signals  
are full duplex and travel on their individual pairs of wires.  
In a TW system, regardless of the manufacturer, the communication is also full duplex, but  
both sides of the conversation travel on the same pair of wires.  
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Figure 5.9 TW and Matrix Signal Flows  
User Station  
TW Signal Flow  
“Generic”  
Microphone  
Bidirectional  
Audio to  
Other Stations  
Sidetone  
Speaker  
+
+
User Station  
Matrix Signal Flow  
“Generic”  
Microphone  
Balanced  
Audio  
To Matrix  
Volume  
Balanced Audio  
From Matrix  
Speaker  
BASIC SIGNAL FLOW DIFFERENCES  
BETWEEN TW & MATRIX INTERCOMS  
In a wireless intercom system, the communication may be full duplex, with the two sides  
of the conversation carried on two separate frequencies. This is the case with all the  
®
Telex RadioCom products. In this way, the signal format is essentially the same as the  
matrix intercom system shown in Figure 5.9.  
In some wireless communications systems (two-way radios for example), both talk and  
listen may share a single frequency, in which case the communication must be half duplex,  
with the users taking turns between talking and listening. A good example of such a  
system is low cost walkie-talkies, wherein the speaker you hear audio from doubles as the  
microphone you speak into when you press the transmit button. In the following  
discussion, we do not concern ourselves with that variety of two-way radio systems  
because those systems are rarely encountered in installations with intercom systems. For  
more detailed information, refer to the chapters on wireless intercom.  
Interconnecting Matrix, PL, and Wireless Systems  
As discussed earlier, the signal format for ADAM , ADAM -CS and Zeus Matrices is  
®
the same as used in the Telex RadioCom line of wireless intercoms. This makes  
interfacing between the two systems very easy, and in fact, Telex provides connectors  
specifically for this on the RadioCom products. To make the two systems work  
together, you simply connect two audio lines.  
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Figure 5.10 Wireless Intercom Interfaced to Matrix Intercom  
Since the RadioCom system is full duplex, with the base station transmitting  
continuously, there is no need for the matrix intercom to provide a PTT (Push To Talk)  
signal to the base.  
In the case of radio systems where the base station is not transmitting continuously, the  
matrix must provide a logic signal corresponding to a user pushing an intercom key to talk  
to that wireless system. ADAM, ADAM-CS, and Zeus all come standard with logic  
signals, with open collector outputs for this purpose, and have available the UIO-256, as  
an accessory, which can provide an actual relay closure, if required.  
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Figure 5.11 GPI/O Implemented PTT (Push-To-Talk)  
2 Way Radio  
Base Station  
GP I/O Interface  
Out  
In  
PTT(n/o)  
Relay Closes Upon  
Talk” Signal to  
+ +  
- -  
2 Way Radio  
“PTT” (Push-to-Talk)  
As mentioned earlier, TW systems are, by definition, two-wire (one pair) communications  
systems, having both talk and listen present at the same time on the same conductors. In  
order to connect a TW intercom system to a four-wire system an interface is required. This  
interface is known by a number of different names, including: hybrid, two-wire to four-  
wire converter, and system interface. Regardless of the name, the function is simple,  
although the technology is not.  
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Figure 5.12 TW to Matrix Interface  
The hybrid, in Figure 5.12, acts as a “traffic cop” allowing the talk signal from the matrix  
to be applied to the bi-directional TW line while blocking its return when the talk signal  
from the TW is presented to the matrix. The effect of the blocking is termed “nulling”, as it  
cancels of the return signal. The effectiveness of the cancellation is driven by many  
factors. Hybrids are generally available from many sources, including intercom  
manufacturers, Gentner, Telos, and others. Telex has two models available, the RTS  
SSA-324, and the RTS SSA-424. Both units are suitable for most applications. The  
primary difference is the SSA-424 is digital and auto-nulling, eliminating the need for  
manual setup and calibration.  
Software Considerations  
Until now, we have concentrated on the physical and hardware issues for a matrix  
intercom system. As noted earlier, the intercom matrix itself is a matrix mixer, which is  
capable of mixing any combination of inputs to any output. A 50-port system is literally a  
50-input by 50-output bus digital mixer. Firmware and software are what turns this digital  
mixer into an intercom system.  
For the following discussion, it is helpful to understand the different roles played by the  
system firmware and software in a matrix intercom system. As system architectures vary,  
and some information is proprietary to each manufacturer, the information being presented  
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here is specific to RTS ADAM, ADAM -CS and Zeus. The basic concepts hold for  
other matrix intercoms on the market.  
A brief word on the architecture of the ADAM , ADAM -CS and Zeus matrix  
intercom systems will set the stage. Zeus is the entry-level matrix and is configured as 24  
ports, and does not include power supply or controller redundancy. ADAM and ADAM-  
CS are expandable systems, and are standard with redundant power supplies and  
redundant auto-switching controllers. Apart from these differences, and the physical  
characteristics, the three matrices are very similar.  
Communications to and from the keypanels is handled by serial data ports, which are  
RS-485 based, and each port controls a group of eight keypanels. The need for addressing  
of the keypanels was covered earlier. The information sent to and received from the user  
stations is stored within the intercom matrix in non-volatile memory.  
Figure 5.13 ADAMand ADAMCS Basic Components  
Note The diagram in Figure 5.13 and the discussion that follows can also be applied, with a few  
minor exceptions, to the Zeus system.  
As seen in Figure 5.13, the intercom system has provisions for an external PC, which is  
used to do initial setups and configurations, including: naming of ports, assigning of PLs,  
creation of IFBs, creation of ISOs, etc. The PC is also useful in monitoring system status  
and for other housekeeping functions.  
The PC is not required for operation of the matrix, except in certain very rare  
circumstances where UPL statements need to act on files, or in response to date  
information. It is perfectly acceptable to use a PC to configure the intercom, and then  
remove the PC. Even without the PC connected, the intercom will function normally. The  
intercom recovers from power failures, and in the case of ADAM and ADAM-CS, primary  
controller failure, all without need for a connected PC.  
Included on the enclosed CD is a copy of AZ-EDIT, the windows-based configuration  
programs for the RTS line of matrix intercom products. These programs can run without  
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a connected matrix and the best way to learn the programs is to install them. An extensive  
help file is provided and the program is laid out in a logical manner.  
Because the configuration software is run on a standard Windows PC, and communicates  
with the matrix via a standard serial RS-232 port, a number of possibilities exist for remote  
configuration, control, and monitoring. One option is to replace the PC with an auto-  
answering modem. This permits the PC, which is running AZ-EDIT, to connect from  
anywhere via telephone lines and remotely control and diagnose the intercom.  
If that notion strikes you as just a bit too insecure, there are a number of available utilities  
such as PC-Anywhere, which can be used to accomplish the same thing in a different  
manner. Install a PC running AZ-EDIT and PC-Anywhere at the matrix location. Use  
another PC, running PC-Anywhere to dial into the PC at the matrix, running PC-  
Anywhere, then supply the required login information, including security password, and  
again, you have full ability to control and monitor the matrix remotely.  
Figure 5.14 Matrix Intercom Remote Control  
Local PC Running  
PC Anywhere  
ADAM  
ADAM CS  
Advanced Digital Audio Matrix  
Remote PC Running  
PC Anywhere  
Phone Line  
Modem  
Modem  
As noted earlier, the differences between system architectures for control of matrix  
intercom systems from different manufacturers are significant. We do not go any further in  
®
describing them, except to point out that in the case of Telex RTS Intercom systems,  
the supplied software is included on the enclosed CD. You are encouraged to play with it.  
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C H A P T E R  
6
C
HAPTER 6  
INTRODUCTION TO WIRELESS  
INTERCOM SYSTEMS  
TOM TURKINGTON  
Introduction to Wireless Intercoms  
Wireless intercoms have a long and important history as part of the communication  
professional’s repertoire. They have gone through many changes and technological  
improvements over the years to bring us to where we are today. The purpose of this  
chapter is to allow you to become familiar with the history, general workings, and special  
considerations of wireless intercoms. This includes their advantages and disadvantages so  
that in the next chapter we may explore the wild, sometimes weird, but almost never  
boring, world of wireless intercom systems design.  
Note The use of the term RF is made extensively throughout this chapter and the next. RF is an  
abbreviation for Radio Frequency. If you are unfamiliar with the term and would like a  
detailed explanation of what RF is, see the definition in the glossary of this book.  
History of Wireless Intercoms  
In the beginning there was wire, and the wire was good. Soon engineers realized if they  
could cut the wires and move the audio, video and communications signals around the  
television venue without encumbering cables, they would have tremendous freedom to  
accommodate ever-increasing production challenges. They also believed that wireless  
transmission of signals would make their job easier by not having to run miles of cable for  
large remote productions. It turned out not to be so simple. Developing wireless  
microphones, wireless cameras and wireless intercom systems would be a trial and error  
adventure that has spanned the last 30 years or more, and it is not over yet!  
In this section, we look back at the history of wireless intercom systems and see what we  
have learned about wireless communications in the process. The original “wireless  
intercom” consisted of two-way radios and (if you were lucky) a headset. The advantages  
were the technology was readily available and it was relatively inexpensive to use. Two-  
ways worked well for some applications, such as pre-show setup and post-show teardown  
where they are still used today in much the same way they were 30 years ago. Two-ways  
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(now often called HTs or Handie-Talkies) have higher operating power which affords  
substantially increased operating range of over a mile or more in some cases. This range  
can be increased to cover an entire city by the use of repeater stations located at the top of  
centrally located buildings.  
Two-way radios did not, however, do as well for the rigors of live television production. In  
live TV, the restrictive nature of HTs was only too evident. First, HTs utilize a half-duplex  
communication scheme. Half-duplex means that while there is bi-directional conversation,  
only one user may communicate at a time and all other users must listen until the person  
who is communicating is finished. During setup this does not pose a huge problem, but  
during a show, when seconds can seem like hours, this can be a real problem. Imagine a  
cameraman is transmitting over a half-duplex HT system, while the director is trying to  
take a new shot or make some other time-critical change. Obviously, a half-duplex system  
would never do.  
Soon after it became apparent that a half-duplex communications system would never  
satisfy the needs of on-air production, a vast array of new HT-based system configurations  
emerged. The greatest of these utilized two HTs on each user and multiple base station  
units in a complex repeater configuration. An interface box allowed users to wear one  
headset that fed both radios at once. While achieving some of the functionality of the most  
basic modern day wireless intercom, the system was bulky, heavy and unreliable due to  
the numerous wires and complexity of setup. While this system was much closer, it still  
did not offer communications professionals the robust functionality and reliability they  
needed for day-to-day operations.  
The next generation of wireless intercoms to hit the scene was truly a breakthrough. It  
eliminated much of the complex wiring and minimized the equipment the user was forced  
to wear. The system consisted of a base station and multiple user beltpack pairs. In the  
base station there was a single transmitter and multiple receivers (one for each wireless  
user). The audio coming from each receiver was put on a single intercom channel or audio  
bus, and was fed to the transmitter as well as an external intercom line. The transmitter  
was a low power, always on unit that maintained constant outgoing information to all  
wireless users. See Figure 6.1.  
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Figure 6.1 The first beltpack based wireless intercom system.  
TRANSMITTER  
RECEIVER  
FOR  
WALK  
AROUND  
1
2
3
4
FOR  
WALK  
AROUND  
1
TRANSMIT ANTENNA  
TO ALL  
WALK AROUND RX’S  
RECEIVER  
ANTENNA FROM  
WALK AROUND TX’S  
ANTENNA SPLITTER  
COMMON TX  
FOR ALL  
WALK AROUND  
PACKS  
RX  
FOR  
WALK  
AROUND  
1
RX  
FOR  
WALK  
AROUND  
2
RX  
FOR  
WALK  
AROUND  
3
RX  
FOR  
WALK  
AROUND  
4
Each user station in the system consisted of two beltpacks, one for transmit and one for  
receive. Two beltpacks were necessary to combat the phenomenon know as desensing,  
where a transmitter in close proximity to a receiver causes the receiver to have greatly  
reduced sensitivity. Desensing is discussed in greater detail in a future section. Each  
wireless user’s transmitter was on a unique frequency which corresponded to their own  
receiver in the base station. All of the wireless users’ receivers were tuned to the same  
frequency which corresponded to the single base transmitter. A single headset with a split  
feed cable eliminated the need for an external headset interface box. See Figure 6.1. By  
utilizing this system, each wireless user could communicate to both hardwired and  
wireless intercom users in a full duplex mode.  
This system, at long last, provided engineers with a reliable and functional solution to the  
wireless communications problem. Future systems would combine the transmit and  
receive beltpacks and incorporate numerous interfacing and operational advantages. We  
look at some of these in the next section.  
Modern Day Wireless Intercoms  
Today’s wireless intercom systems are technological giants compared to their earlier  
predecessors. They allow users to “cut the cable” of hardwired party-line systems and  
move about freely within the system’s operational range. Modern wireless intercoms can  
be either party-line intercom systems or individual beltpack systems that allow users to  
operate independently from other wireless users. Good quality systems can be seamlessly  
attached to existing hardwired communications systems commonly used in broadcast and  
other facilities. As discussed previously, modern, high quality wireless intercoms offer a  
distinct advantage over traditional, two-way radios in that they offer a more natural full-  
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duplex operation. This enables all users on the system to speak and hear other users  
simultaneously without “covering” other users’ transmissions.  
The demands of modern broadcast productions make the full-duplex operation of wireless  
intercom systems an absolute necessity for stage managers, lighting and audio technicians,  
or any professional who has to deal with the breakneck speed and complexity of television  
productions.  
The spread of digital television (DTV) and the ever-increasing number of wireless users  
has made the available frequency spectrum a more difficult place in which to find  
available channels for wireless intercoms. The spectrum has also become a lot smaller,  
especially considering that four television channels (24 MHz of spectrum) have been  
reallocated for public safety use and the upcoming reallocation of UHF TV channels 60  
through 69 (60 MHz of spectrum). Broadcast professionals now have to consider such  
factors as the compatibility of frequencies with each other, as well as, how to best avoid  
interference with local TV transmitters. We discuss these topics in more detail, later.  
Unlike wireless microphones that operate only in one direction, wireless intercoms have  
more specific frequency spectrum requirements because of the relationship between the  
transmitter and receiver frequencies. Each intercom (if it is to be full-duplex) must have at  
least one system transmitter frequency that broadcasts to all beltpacks and one receiver  
frequency for each individual beltpack in the system. For a four beltpack system, also  
known as a four up, that means it must have a minimum of five total frequencies. See  
Figure 6.2 An example of a modern day wireless intercom system.  
RECEIVER &  
TRANSMITTER  
FOR  
WALK  
AROUND  
1
2
3
4
TRANSMIT ANTENNA  
TO ALL  
WALK AROUND RX’S  
RECEIVER  
ANTENNA FROM  
WALK AROUND TX’S  
ANTENNA SPLITTER  
COMMON TX  
RX  
FOR  
WALK  
AROUND  
1
RX  
RX  
FOR  
WALK  
AROUND  
3
RX  
FOR  
WALK  
AROUND  
4
FOR ALL  
WALK AROUND  
PACKS  
FOR  
WALK  
AROUND  
2
Each beltpack must have a receiver set to the base transmit frequency and a transmitter set  
to its own unique receiver in the base. Due to a phenomenon mentioned earlier called  
desensing, these two frequencies must have a fairly large frequency separation, typically at  
least 12 MHz for VHF systems, and even more for UHF, or the transmitter will interfere  
with the receiver’s operation.  
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The answer to the frequency problem is to utilize a digitally synthesized, frequency agile  
system. That may sound simple enough in theory, but in reality, designing such a product  
is a totally different matter. A digitally synthesized, frequency agile system must not only  
incorporate a superior design with high-quality filtering to withstand the rigors of an  
overcrowded frequency spectrum, but it must also offer an ergonomically designed user  
interface that allows ease of frequency selection and operation. End users must experience  
the same ease of operation they get from their existing two-wire beltpacks.  
To date, the chief limitation to most wireless intercoms (other than finding available  
spectrum) has been they are inherently one-channel in nature while the most common  
hardwired intercom system from RTS (used in virtually all TV broadcast trucks and  
facilities) is two-channel. Two-channel operation allows users to switch easily from one  
intercom channel to another. This allows a stage manager, for instance, to communicate  
with the producer and then switch over to the director circuit as necessary. Two-channel  
operation has become the hardwired industry standard and users who have increasingly  
relied on wireless intercoms must be able to employ that technology in wireless form  
without having to deal with huge racks full of equipment.  
Wireless intercom systems that can operate in high RF environments must not only offer  
interference resistant operation, but must utilize design techniques that will not interfere  
with other wireless equipment like wireless microphones and IFBs. Another key to a  
wireless intercom’s successful operation and coexistence with DTV is its ability to avoid  
strong local TV stations, as well as, coordinate multiple system frequencies. This holds  
true whether the system is VHF or UHF, fixed-frequency, frequency-agile or synthesized.  
Utilizing the minimum power necessary is absolutely critical if wireless intercoms are to  
coexist with other low-power wireless equipment. The utilization of intelligent systems  
that reduce beltpack transmitter power levels as they get closer to the base station can  
greatly decrease the harmful interference that can be associated with wireless  
communications gear.  
Future wireless intercoms (see Figure 6.3) will need to provide users with frequency  
agility, high-end filtering, RF power management, ease of use, two-channel operation,  
extended battery life, small lightweight beltpack and a user interface that allows  
operational and frequency parameters to be easily set and checked without the use of  
external equipment, such as a laptop computer or special interface box.  
Figure 6.3 The RadioCom™ BTR-800 System is an outstanding example of the next generation  
of wireless intercom systems.  
As wireless intercom applications for broadcast professionals continue to grow more  
complex and challenging, the need for products that can meet these challenges will also  
grow accordingly. All these factors and more, as discussed in this chapter, and in the next  
chapter, must be considered when looking at the quality and functionality of a modern  
wireless intercom system.  
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Special Considerations  
Wireless communications are here to stay. They have become an integral part of the total  
professional communications package. There are, however, many factors associated with  
wireless that need to be understood and addressed that do not come into play with  
hardwired communications systems. In this section, we look at the special considerations  
that must be considered when deciding whether or not to implement a wireless system.  
The first area of study is the RF spectrum and how it can be used to implement a wireless  
intercom system. Traditionally, wireless intercoms have been a function of broadcast  
television productions, and as such have used, at least in part, a spectrum that falls under  
FCC Code 47 CFR, Part 74 in addition to itinerant frequencies. The spectrum most  
commonly used falls into two areas: VHF systems from approximately 154 MHz to 216  
MHz, and UHF systems from 460 MHz to 608 MHz and 614 - 806 MHz. As mentioned in  
an earlier section, large chunks of this spectrum have either been reallocated, or will soon  
be reallocated. The FCC has found that auctioning spectrum is a good way for the  
commission to move from an expense center to a profit center, and they are pursuing it  
with a passion.  
Wireless intercoms, like any other wireless system, require at least one transmitter to  
function. Under FCC rules, all transmitters must be licensed prior to operation (there are  
some very low power transmitters that can operate under Part 15 and do not need to be  
licensed, but that doesn’t apply to any modern RF intercom systems). There are different  
forms to obtain various types of licenses depending on what area of the spectrum your  
system will operate in, who will be operating the system, and what the system will be used  
for. The law is very clear in that no one is permitted to operate a transmitter typically used  
for wireless intercom systems without first obtaining an FCC license.  
Wireless equipment often operates in areas of the RF spectrum that are designated for TV  
channels, but are unused in a given area. In all cases low power transmitters used by  
wireless intercoms and wireless mics must operate on a secondary, non-interfering basis.  
This means that wireless users must not cause harmful interference to television or other  
receivers, and must accept all interference sources. In keeping with this, the FCC rules  
state that VHF systems must not be operated within 50 miles of a television transmitter  
occupying a similar spectrum. The rules further state that UHF systems must not be  
operated within 75 miles of a television transmitter occupying a similar spectrum. See  
Figure 6.4, for a depiction of what a television station’s assigned spectrum looks like.  
Refer to Table 6.1 for the standard frequency allocations of television transmitters.  
Figure 6.4 NTSC channel configuration.  
Video Carrier  
NTSC Channel Configuration  
Audio Sub  
Guard Band  
Chroma Sub  
Slot Area  
TV Channel  
End Freguency  
TV Channel  
Start Frequency  
0 MHz  
1
2
3
4
5
1
6 MHz  
1.25 MHz  
4.8295 MHz  
5.75 MHz  
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Table 6.1 Standard US television channel allocations.  
Chan  
Start  
Video  
Chroma  
Audio  
2
54  
55.250  
58.8295  
59.750  
3
60  
61.250  
64.8295  
65.750  
4
66  
67.250  
70.8295  
71.750  
5
72  
73.250  
76.8295  
77.750  
6
78  
79.250  
82.8295  
83.750  
7
174  
180  
186  
192  
198  
204  
210  
470  
476  
482  
488  
494  
500  
506  
512  
518  
524  
530  
536  
542  
548  
554  
560  
566  
572  
578  
584  
590  
596  
602  
608  
175.250  
181.250  
187.250  
193.250  
199.250  
205.250  
211.250  
471.250  
477.250  
483.250  
489.250  
495.250  
501.250  
507.250  
513.250  
519.250  
525.250  
531.250  
537.250  
543.250  
549.250  
555.250  
561.250  
567.250  
573.250  
579.250  
585.250  
591.250  
597.250  
603.250  
178.8295  
184.8295  
190.8295  
196.8295  
202.8295  
208.8295  
214.8295  
474.8295  
480.8295  
486.8295  
492.8295  
498.8295  
504.8295  
510.8295  
516.8295  
522.8295  
528.8295  
534.8295  
540.8295  
546.8295  
552.8295  
558.8295  
564.8295  
570.8295  
576.8295  
582.8295  
588.8295  
594.8295  
600.8295  
606.8295  
179.750  
185.750  
191.750  
197.750  
203.750  
209.750  
215.750  
475.750  
481.750  
487.750  
493.750  
499.750  
505.750  
511.750  
517.750  
523.750  
529.750  
535.750  
541.750  
547.750  
553.750  
559.750  
565.750  
571.750  
577.750  
583.750  
589.750  
595.750  
601.750  
607.750  
8
9
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  
35  
36  
37  
Radio Astronomy  
Only  
38  
39  
40  
41  
42  
43  
44  
45  
614  
620  
626  
632  
638  
644  
650  
656  
615.250  
621.250  
627.250  
633.250  
639.250  
645.250  
651.250  
657.250  
618.8295  
624.8295  
630.8295  
636.8295  
642.8295  
648.8295  
654.8295  
660.8295  
619.750  
625.750  
631.750  
637.750  
643.750  
649.750  
655.750  
661.750  
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Table 6.1 Standard US television channel allocations.  
Chan  
Start  
Video  
Chroma  
Audio  
46  
47  
48  
49  
50  
51  
52  
53  
54  
55  
56  
57  
58  
59  
60  
61  
62  
63  
64  
65  
66  
67  
68  
69  
662  
668  
674  
680  
686  
692  
698  
704  
710  
716  
722  
728  
734  
740  
746  
752  
758  
764  
770  
776  
782  
788  
794  
800  
663.250  
669.250  
675.250  
681.250  
687.250  
693.250  
699.250  
705.250  
711.250  
717.250  
723.250  
729.250  
735.250  
741.250  
747.250  
753.250  
759.250  
765.250  
771.250  
777.250  
783.250  
789.250  
795.250  
801.250  
666.8295  
672.8295  
678.8295  
684.8295  
690.8295  
696.8295  
702.8295  
708.8295  
714.8295  
720.8295  
726.8295  
732.8295  
738.8295  
744.8295  
750.8295  
756.8295  
762.8295  
768.8295  
774.8295  
780.8295  
786.8295  
792.8295  
798.8295  
804.8295  
667.750  
673.750  
679.750  
685.750  
691.750  
697.750  
703.750  
709.750  
715.750  
721.750  
727.750  
733.750  
739.750  
745.750  
751.750  
757.750  
763.750  
769.750  
775.750  
781.750  
787.750  
793.750  
799.750  
805.750  
Having touched briefly on the FCC rules, I must inform you the vast majority of users, not  
only of wireless intercoms, but of wireless mics and IFBs as well, do not obtain licenses.  
In fact, historically, many users of UHF wireless gear, outside of television broadcasters or  
people working with broadcast entities, could not even qualify to get an appropriate  
license. Right, wrong or indifferent, this has been the case. Telex Communications, Inc.  
strongly recommends that every wireless system be licensed and operated in strict  
accordance to FCC rules. Your local wireless dealer can help you understand the  
requirements and regulations that apply to you.  
There has been progress though. The FCC has, as of late, worked with users, other than  
broadcast, to facilitate a win-win licensing scheme that may, in the future, help to ensure  
all systems are licensed and operated according to FCC rules. In any case, each user must  
in all good conscience, research his ability to license and operate wireless equipment, and  
govern equipment purchase and implementation accordingly.  
In addition to the FCC rules, wireless users must also consider how best to avoid harmful  
interference to ensure uninterrupted and intelligible communications. One of the best ways  
to go about selecting the area of spectrum you will use is to do a frequency survey. By  
using a spectrum analyzer or other specialized receiver, it is possible to look at potential  
interference sources and avoid them. Picking an area of spectrum that is free from external  
interference sources will go a long way in helping you select frequencies that offer trouble  
free operation.  
In addition to a clear spectrum, you must also consider the intermodulation affects of the  
specific frequencies you pick. An in depth study of this topic is beyond the scope of this  
book, but we will touch on the subject to give you a general overview.Intermodulation  
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(IM) or intermod as it is often called, happens when two or more frequencies mix in a non-  
linear device and produce a number of related different frequencies known as  
intermodulation products. We look at intermodulation in more detail in the next chapter,  
but suffice to say, choosing a manufacturer or dealer that is qualified to pick  
intermodulation free frequencies is a must.  
Now let’s look at cost. Wireless intercom systems cost substantially more at initial  
purchase than do hardwired communications systems. For a comparable number of users,  
wireless systems cost between two to ten times as much as hard wired partyline systems,  
depending on system type and configuration. Because of this increased cost factor, it is  
important to determine which members of the production team must be wireless and which  
can be tethered by a wire. Of course, everyone wants to be wireless and has a great reason  
why they need a wireless beltpack, but in the end you must make the budget meet the  
overall production needs.  
Generally speaking, the added cost and special consideration factors that wireless  
communications systems have to be concerned with are far outweighed by the increased  
flexibility and functionality they offer. It is important to choose a wireless system with all  
of the facts and considerations in front of you so you can have years of trouble free  
operation to come.  
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C H A P T E R  
7
C
HAPTER 7  
DESIGN OF WIRELESS  
INTERCOM SYSTEMS  
TOM TURKINGTON  
Introduction  
The design, and subsequent operation, of a wireless intercom system is, like any wireless  
network, highly dependent on numerous factors. Some of these factors you will have  
control over, but many you will not. The key to successful wireless system design, whether  
it be intercoms, talent audio, or roving camera, is to gather the information related to all of  
the variables before you get started and then match the system components and  
architecture to your specific requirements. There is no such thing as a one size fits all  
wireless system. In this chapter, we explore some Radio Frequency (RF) theory that allow  
you to have a better understanding of how RF works. We will also look at many of the key  
components of a wireless communications system and how they go together to create the  
desired effect.  
Back-to-Basics  
In this section, we discuss the theory of how RF signals act and how they are affected by  
various conditions. There is some math discussed here, but only enough to convey the  
principles at hand. The idea is to give you a good working knowledge of RF principles, not  
make you an expert in Bessel functions. Old RF pros can probably skip this section,  
although a refresher of this material is almost always appropriate.  
First, let’s answer the question, “What is RF?” Contrary to popular belief, the frequency of  
a signal does not determine whether it is an RF signal or not. The defining factor for RF  
signals is the medium through which they propagate. All energy that travels in waves  
propagates through some medium which allows the wave to move from one location to  
another. In the case of sound, the medium is typically air or water or some other physical  
mass. RF signals on the other hand, regardless of frequency, always propagate or move  
through the electromagnetic spectrum. Where as sound needs some physical mass to  
move, RF signals do not. The electromagnetic spectrum exists everywhere (as far as we  
know), and enables RF signals to move through the vast vacuum of space where sound  
waves could never go.  
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A brief look at the properties of the electromagnetic spectrum can tell us a lot about the RF  
signals that move through it. As you can see, the name electro-magnetic is really a  
combination of two words, electron (or electronic) and magnet (or magnetic). The reason  
for this is that waves that propagate in the electromagnetic spectrum have two separate and  
distinct components, an electrical and a magnetic. As you can see in Figure 7.1, these two  
components exist at right angles to each other, as well as, to the direction of propagation.  
The electrical component, or field as it is called, is represented by the letter E and the  
magnetic field by the letter H. (No, I don’t know why they use H, but they do!)  
Figure 7.1 The E an H fields exist in two separate planes, 90° apart from each other.  
E
90°  
FIELD  
Z
Y
DIRECTION OF  
PROPAGATION  
H
FIELD  
X
RF signals at different frequencies have different propagation characteristics and are  
affected by external forces in different ways. The reason for this is the ratio of the  
magnitudes of the electrical and magnetic components of an RF wave vary dramatically as  
frequency changes. Generally speaking, the magnetic component of an RF wave is much  
greater than the electrical component at very low frequencies. As the frequency increases,  
the electrical component increases and the magnetic component decreases, until, at very  
high frequencies, the electrical component is much greater than the magnetic.  
This is not just “gee whiz” information. The different makeup of RF waves at different  
frequencies is what allows us to use the signals for different and sometimes unusual  
applications. For instance, at super low frequencies, such as 5 Hertz, where the magnetic  
component is extremely dominant, the US Navy has been able to propagate RF signals  
through the Earth’s core to communicate with submarines on the other side of the world.  
Try that at 13 GHz! In a more pertinent example, at much higher frequencies the highly  
reflective nature of the mostly electrical component wave can cause self-interference,  
known as multipath. Multipath can cause an RF signal to be unusable at a very short  
distance from the transmitter if not properly handled. We will discuss multipath in more  
detail later in this chapter.  
Now that we know what RF is, we can discuss what it does, how we can use it and how it  
is affected by outside forces. In its most basic form, an RF system puts information on an  
RF signal, sends it to a remote location and retrieves the information in exactly the same  
form as it originally existed. Let’s take a look at this most basic system and define some  
terms so we can talk about this process more easily. Refer to Figure 7.2.  
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Figure 7.2 An example of wireless transmission and reception.  
TRANSMIT  
ANTENNA  
RECEIVER  
ANTENNA  
TRANSMISSION  
LINE  
TRANSMISSION  
LINE  
SOURCE  
SIGNAL  
COPY OF  
SOURCE  
SIGNAL  
TRANSMITTER  
RECEIVER  
In Figure 7.2, the transmitter is a device that has an input for information, audio, data, or  
some other form of intelligence called a source signal, that needs to get from here to there.  
The transmitter then takes that information and puts it onto an RF signal. The RF signal is  
called a carrier because it, in effect, carries the source signal as it propagates. The process  
of actually putting the source signal onto the carrier is called modulating the carrier, which  
normally is referred to simply as modulation. The carrier which has had the source signal  
applied is then broadcast into the air (actually the electromagnetic spectrum) via an  
antenna. The antenna is a transducer that allows the carrier to be efficiently broadcast or  
received.  
Once the signal is broadcast into the air, it propagates out away from the transmit antenna  
and eventually reaches the receive antenna. The area between the transmit antenna and the  
receive antenna is called the propagation path, or just path. At the receive antenna, the  
signal, which is now much weaker, is collected and enters into the receiver. The receiver’s  
job is to find the one unique carrier from the transmitter and strip off the source signal so it  
exactly matches the original information. This process is called demodulation.  
Now, let’s look at the RF wave as it moves along the propagation path. We know that RF  
propagates or moves from one point to another, and that propagation can be affected by the  
frequency of the wave. Now we’ll find out how RF waves normally act in typical  
environments. You can think of an RF signal that radiates out into open space from a  
specific point, such as a transmit antenna, like the waves generated by throwing a pebble  
into a pond as shown in Figure 7.3. The energy carried by the wave moves away from the  
original point in all directions equally and each vector that can be drawn from the center  
point represents RF energy traveling away from the point of origin in a straight line as  
Figure 7.3 An example of electromagnetic waves being radiated.  
In addition, the RF wave continually gets weaker as it moves away from the transmit  
antenna. The rate at which the wave becomes weaker can be calculated via the inverse  
2
square law 1/D where D = distance traveled by the wave. This is a very important concept  
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because it shows why a wave that travels twice as far as another wave of equal magnitude  
is not half as strong. Take the following example:  
Two transmitters TXA and TXB both emit signals that are exactly the same at 1 Watt of  
power. The signal from TXA travels 10 units. Power at that point can be calculated by  
2
1/10 x 1W or 0.01 x 1W. That means there is 0.01W of the TXA signal left after it has  
traveled 10 units. Now let’s say that the TXB signal travels twice the distance of TXA  
2
or 20 units. Power at that point can be calculated by 1/20 x 1W or 0.0025 x 1W. That  
means there is 0.0025W of the TXB signal left after it has traveled 20 units. As you can  
see, the signal that traveled twice as far was not ½ the power, but ¼ the power of the  
first signal.  
Because of the inverse square law, the effective radiated power (ERP) of a given  
transmitter must increase by a factor of four times to achieve twice the operating range.  
This information is important in determining the necessary power for a wireless system for  
a given range. It is always important to use the minimum power necessary to accomplish  
the task at hand so that excess power does not affect other systems and cause undue harm.  
The theoretical range of an RF system is important to know, but it is the functional range  
you must be more concerned with. The functional range of a system takes into account a  
certain cushion factor called fade margin that will ensure the signal coming from the  
transmitter to the receiver will not only be detectable, but will also be usable. This is less  
of a concern in communications systems as you can tolerate less fade margin than in an  
on-air wireless microphone system, because a small momentary dropout will not critically  
affect communications as it would program audio.  
RF waves travel away from the source in a straight line until that path is interrupted or  
disturbed by some outside influence. Figure 7.4 shows an RF wave being reflected and  
thus changing the path of some of the RF energy. If you remember earlier when we  
mentioned multipath, this reflected energy is the cause of that phenomenon. Before we can  
discuss multipath in more detail, though, we must learn about another aspect of the RF  
wave and how it changes when it comes in contact with a reflective surface.  
Figure 7.4 An example of reflected RF waves.  
REFLECTED SIGNAL  
TX  
Antenna  
RX  
Antenna  
DIRECT SIGNAL  
Polarization is the term that describes the orientation of an RF wave. Remember back to  
when we discussed the two components that make up an RF wave, the electrical and the  
magnetic. We said that the E field was the electrical component and that the H field was  
the magnetic component. The polarization of an RF signal is determined by the orientation  
of the E field. If the E field is perpendicular to the plane of the Earth, the wave is said to be  
vertically polarized. If the E field is parallel to the plane of the Earth, the wave is said to be  
horizontally polarized. See Figure 7.5.  
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Figure 7.5 The orientation of the radiator (antenna) determines the polarization, and therefore, the  
orientation of the E and H fields.  
E Field  
Vertical  
H Field  
Vertical  
H Field  
Horizontal  
E Field  
Horizontal  
VERTICALLY  
POLARIZED WAVE  
HORIZONTALLY  
POLARIZED WAVE  
Transmit and receive antennas of the same system must be oriented in the same direction  
(plane) to have a proper transfer of the carrier. In theory, if a transmit antenna is oriented  
vertically, thus producing a vertically polarized carrier, and the corresponding receive  
antenna is oriented horizontally, the receive antenna will not be able to see the vertically  
polarized wave at all. In practice, there will always be some polarization shift in the path  
and the receiver will see a very small signal if it is close enough to the transmitter. To  
avoid this problem, antennas in a given RF system should always have similar orientation.  
There are other forms of polarization, such as circular polarization, which can be used to  
help counteract the effect of multipath, but for now we will use horizontal and vertical  
polarization for our discussion. It is important to note here the difference between  
polarization and phase, as the two terms are often confused. Phase refers to the  
relationship of the sinusoidal energy of two or more waves, not to the orientation of the  
electrical component. See Figure 7.6. Two identical waves that are in phase, and are  
combined, add to make a larger wave. Two identical waves that are out of phase by exactly  
180°, and are combined, cancel each other out. See Figure 7.7. Waves that are not exactly  
identical in either frequency, amplitude, or phase will have a composite sum that may  
increase the overall amplitude at some points, and either reduce or eliminate the overall  
amplitude at others. See Figure 7.8. It is critical to have a good understanding of these two  
principles as we start to discuss multipath.  
Figure 7.6 Waves that are in phase combine to form a larger wave.  
Figure 7.7 Waves that are out of phase cancel each other.  
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Figure 7.8 An example of combining waves that are not 180° out of phase.  
Interference  
As mentioned earlier, multipath can be described as a form of self interference caused  
when a reflected RF carrier arrives at the receive antenna along with an RF carrier that has  
taken a direct path. See Figure 7.9. The reason multipath is so detrimental to the successful  
operation of an RF system has to do with the nature of the relationship of the reflected  
signal to the direct path signal.  
Figure 7.9 An example of multipath in its most basic form.  
REFLECTED SIGNAL  
TX  
Antenna  
RX  
Antenna  
DIRECT SIGNAL  
The direct path carrier takes the most direct, and consequently, the shortest path from  
transmitter to receiver. The reflected carrier, on the other hand, takes a longer path, from  
the transmitter to the reflective surface, and from the reflective surface to the receiver. The  
waves leaving the transmitter antenna are all in phase, but because the direct carrier and  
the reflected carrier travel different distances, thus taking slightly different lengths of time,  
the two carriers are out of phase, and of different amplitudes (remember the inverse square  
law), when they reach the receive antenna. The two carriers are combined at the receive  
antenna and, being out of phase, they cancel each other out so that little or nothing can be  
detected by the receiver. This causes a momentary interruption in the RF wave, which is  
called a dropout. Dropouts are manifested in audio RF systems by a loud click or pop  
surrounded by noise. Proper system design and careful antenna placement can go a long  
way to reducing the effects of multipath on a wireless communications system. We discuss  
how to avoid multipath later in this chapter.  
The next concept that you must be familiar with to move forward in the design of your  
wireless intercom system is receiver desensitization or desensing. As mentioned earlier,  
desensing happens when a transmitter is in close proximity to a receiver, even if that  
transmitter is not on or near the receiver’s operating frequency. Receiver desensitization  
happens because receivers must maintain critical voltage and current levels throughout the  
front end stages, and a strong (i.e. close by) transmitter can cause these levels to vary  
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greatly. As these levels are changed over a wide range, the receiver performance will be  
greatly degraded. The greater the physical distance between transmitter and receiver, the  
less the receiver will be affected. Likewise, the greater the frequency separation between  
the two, the less the receiver performance will be affected.  
Selecting frequencies that are “clean,” or free from the effects of intermodulation  
products, is essential to good wireless communications. Intermodulation is often one of the  
prevalent sources of system interference. We touch on just the basics of intermod here so  
you can get a sense of what it is and how it works. As stated in an earlier chapter,  
intermodulation, or IM as it is often called, happens when two or more frequencies mix  
in a non-linear device and produce a number of related different frequencies known as  
intermodulation products. These IM products can cause severe, harmful interference to a  
wireless intercom system if they fall on or near any of the operating frequencies of that  
system.  
For intermodulation interference to take place, at least two transmitters must be  
broadcasting at the same time on frequencies that have a definite, calculable relationship  
with the affected receiver. In many cases of IM interference the receiver can detect and  
demodulate the IM product almost as cleanly as if one of the interfering transmitters was  
on the operating frequency of the receiver. Turning off either one of the two (or more)  
transmitters will cause the IM interference to cease.  
Because there is a fixed and calculable relationship between frequencies, intermodulation  
products can be calculated and avoided. Here is an example of some of the more common  
IM products that can be calculated:  
2A – B = C  
2(651.500 MHz) – 650.000 MHz = 653.000 MHz  
A – B + C = D  
184.000 MHz – 190.600 MHz + 188.200 MHz = 186.400 MHz  
3A – 2B = C  
3(518.200 MHz) – 2(520.500 MHz) = 513.600 MHz  
There are, of course, many other combinations that can cause harmful interference. These  
examples give you a good idea of how the calculations work, but for comprehensive  
frequency selection, an advanced computer program must be used.  
It is important to note that intermod products are not created in the air, they are the result  
of the mixing of signals in non-linear devices such as amplifiers or other usually active  
elements. The most common place for this mixing to take place is in the active receiver RF  
circuitry. Once RF signals get past the receiver front end and get to the first RF amplifier  
and beyond, mixing of those signals can and will take place. If the intermod products that  
are generated fall on or near the operating frequency of the receiver, harmful interference  
will be heard.  
Good quality receivers have front ends that are passive, linear devices that limit the range  
of frequencies that will enter the rest of the receiver circuitry. Making sure you pick  
wireless intercoms with well designed front ends, is critical to proper operation in hostile  
RF environments.  
The next most common place for IM products to be generated is in the final amplifier of a  
transmitter. Because the transmit antenna can and does also act as a receive antenna,  
strong RF signals from nearby transmitters can make their way into the non-linear, active,  
final amplifier and produce intermod products. These products can then be broadcast out  
with the intended signal and cause harmful interference. It is important to note that IM  
products do not have to end up exactly at a receive frequency. Sometimes, they can be of  
sufficient power at relatively close frequencies to create a desensing situation.  
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Reducing the effect that intermodulation can have on your wireless intercom system  
comes down to a few important principles. First, and foremost, you must pick frequencies  
that are intermod free with each other and with surrounding transmitters. Second, you  
should pick wireless intercom systems that have well designed receivers and transmitters  
with appropriate passive filtering. Third, you must manage the positioning of antennas and  
beltpacks within the system to optimize operational potential.  
Transmitters and Receivers  
To be able to select the appropriate wireless communications equipment you need to  
understand the basic operations of transmitters and receivers, and which aspects are  
important to proper operation. In this section, we cover generic functional block diagrams  
of transmitters and receivers, and point out the most critical aspects of each. While design  
variations are great between manufacturers, the block diagrams that follow represent the  
most basic designs.  
Let’s start with the transmitter (see Figure 7.10). The primary job of the transmitter is to  
take in a source signal, modulate it onto an RF carrier, and then deliver it to the transmit  
antenna for broadcast into the electromagnetic spectrum.  
Figure 7.10 Transmitter block diagram.  
Filter &  
Impedance  
Matcher  
Amplifier  
Multiplier  
Final  
Amplifier  
Mic/Line  
Input  
Compressor  
Modulator  
SOURCE  
SIGNAL  
TO  
ANTENNA  
First, an audio signal is brought in and any necessary audio amplification is done via the  
Mic/Line Input section. Next, the signal is sent through a Compressor circuit to ensure the  
levels of the input signal are held within acceptable limits. The signal is then mixed with a  
reference frequency in the Modulator. This reference frequency can be the main carrier  
frequency, or (as in most cases) it is a base frequency that results in a composite signal.  
Note There are many different types of Modulators, as well as, many different types of  
modulation. A detailed discussion of their detailed workings is beyond the scope of this  
book.  
The signal is then sent to the Amplifier/Multiplier. If the signal is already on the desired  
transmit frequency, it is only further amplified. If, however, the signal is only a composite  
signal, then it is frequency multiplied to reach the desired operating frequency. The signal  
is then sent to a Final Amplifier where it reaches its maximum power level. Usually this is  
slightly more than the actual output power as measured at the output connector. The reason  
for this is to make up for the losses induced by the Output Filter and Impedance Matching  
circuit(s).  
The Output Filter and Impedance Matching circuits are generally passive and therefore, do  
not provide any means of amplification. As such, they can only reduce the output signal  
levels. The Output Filter is a very narrow bandpass filter that removes any unwanted  
harmonics from the signal. The Impedance Matcher provides the necessary interface  
between the transmitter and the Antenna/Transmission Line to ensure maximum power  
transfer. If the Antenna/Transmission Line are not properly matched, significant loss can  
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occur. In some situations, it is possible for this to cause damage to either the transmitter,  
transmission line, and/or antenna.  
Now let’s look at the receiver and it’s primary functional aspects (see Figure 7.11). The  
receiver in a wireless system is the exact compliment of the transmitter, but is usually  
much more sophisticated and complex in design. Its job is to receive the signal from the  
receive antenna and extract the source signal so that it matches the original exactly. In  
practice, there will always be some modification or distortion of the source signal in the  
course of transmission, but good quality wireless systems minimize this to a level that is  
indistinguishable.  
Figure 7.11 Receiver block diagram.  
Ist IF  
Filter  
2nd IF  
Filter  
RF  
Amplifier  
Front End  
Filter  
Mixer  
Mixer  
FROM  
ANTENNA  
1st Local  
Oscillator  
2nd Local  
Oscillator  
Expander  
Demodulator  
TO  
AUDIO PROCESSOR  
As in the transmitter, the antenna will be covered in the next section. The receiver starts  
with the front-end filter. The front-end filter is extremely important to successful operation  
in high RF level environments. The front-end filter is the first line of defense. Its job is to  
limit the number of potential interfering frequencies that could affect the receiver. It is  
usually a passive, linear section and it must be impedance matched to the antenna for  
proper signal transfer. Linearity is the most important factor in a front end, even more so  
than how tight or narrow the section is. A high degree of linearity will ensure that no  
intermodulation products are generated in the front end before extraneous RF signals are  
filtered out. Having a front-end that is relatively tight and that is extremely linear is critical  
if the system is to work properly under worst-case RF scenarios.  
The next section of the receiver is the first RF amplifier. The first RF amp’s job is to take  
the extremely low level RF signal coming through from the front end and bring it up to a  
usable level. The incoming RF signal at the first RF amp can vary dramatically from less  
than 0.5 µV to almost the value of the transmitter output. The key for the first RF amp is  
that it should be able to handle very small, as well as, relatively large incoming signals  
within it’s linear region of operation. See Figure 7.12. To maintain a good linear region,  
RF amps normally require a high current drain which can negatively impact battery life. A  
compromise between linearity and effective battery life must be managed carefully.  
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Figure 7.12 Good linearity is a must for faithful signal reproduction.  
GOOD COPY  
DISTORTED COPY  
The next receiver section we look at is the first local oscillator (LO). The job of the first  
LO is to provide a reference signal that is a fixed distance from the operating frequency of  
the system. It is very important the first LO be stable over a wide range of temperatures. In  
fixed crystal systems, one or more crystals cut to a specific relationship of the operating  
frequency are used to generate this highly accurate reference signal. A different crystal is  
necessary for each operating frequency. In synthesized units, a single reference crystal is  
used in a phase-lock-loop to provide the signal for any operating frequency needed by the  
receiver.  
The First LO feeds the reference signal to the Mixer where the incoming RF carrier is  
mixed, or beat with the reference signal, to produce the First Intermediate Frequency (IF).  
The frequency of the First IF is the difference in frequency between the incoming RF  
carrier and the First LO reference signal. Unfortunately, what comes out of the Mixer is  
not a just the First IF, it is the algebraic sum and difference of the two signals being mixed  
plus numerous other harmonic junk. To get to the point where you have a clean First IF  
consisting of just the desired frequency, the signal is passed through to the First IF Filter.  
The First IF Filter is extremely important to proper receiver operation. It is a passive, very  
narrow (often 50 to 250 KHz), and precise filter that eliminates the vast majority of  
unwanted signals so the true First IF can be processed correctly. It is very important that  
the First IF Filter be sharp, as well as, very linear. Any non-linearity in the filter will cause  
unwanted distortion of the demodulated source signal.  
Next, the signal is sent to the second Mixer where a second IF frequency is produced in the  
same way the First IF was obtained. The Second LO is the same frequency for any RF  
carrier frequency the receiver is capable of because the first LO takes care of the frequency  
differences and produces an always-constant First IF frequency for the Second IF to  
handle. Again, the Second IF signal as it leaves the Second Mixer is full of harmonic junk  
and needs to be filtered by the Second IF Filter. The Second IF filter eliminates unwanted  
harmonic energy and prepares the signal to be demodulated.  
The next phase of the receiver is the Demodulator. There are several types of  
demodulators used by wireless manufacturers today and it would be beyond the scope of  
this book to discuss them all in detail. Suffice to say, through a type specific process the  
Demodulator extracts the source signal from the Second IF carrier. The quality of the  
Demodulator circuit is critical to good audio quality. Any type of signal distortion or  
modification that takes place in the demodulation process will cause the final signal to be a  
less than perfect reproduction of the original source signal.  
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Antenna & Cable Considerations  
Antennas and cables (transmission lines) are one of the least thought about aspects of a  
wireless system among RF novices. Good quality antennas and cables, however, are some  
of the most important aspects to establishing and maintaining a quality RF link. In  
addition, because antennas and cables are more easily changed and in general are less  
expensive than other system components, they can be a “quick fix” for many RF problems  
found in common wireless communications systems. In this section, we cover some of the  
more common types of antennas and the operating characteristics of each. In addition, we  
take a look at coaxial cable and what is required when selecting cable for your system.  
To adequately look at and evaluate the strengths and weaknesses of some common  
antenna types, we first must have a very general knowledge of antenna theory. Antenna  
theory is a course of study unto itself and we will not even scratch the surface in this brief  
section, but it should be enough to understand some basic principles. To start, let’s ask the  
question, “What is an antenna?” To answer that question we must look at what an antenna  
does. In a transmitter, the antenna takes electrical energy and allows it to be propagated  
out into the electromagnetic spectrum. In a receiver the antenna “gathers” the RF signal  
and converts it back into electrical voltages and currents. In either case, the antenna acts as  
a transducer to change the form of the RF energy.  
All real world antennas have a pattern or specific shape with which the RF energy is  
released or captured. There is no such thing as an antenna that sends energy out equally in  
all directions. The primary reason for this is that you have to get the signal to the antenna  
via a transmission line and that line must be connected to the antenna some how. That  
connection will always cause a disruption or altering of RF propagation in some direction.  
In theory though, it is nice to talk about a perfect antenna. This perfect antenna radiates  
equally in all directions and is called an isotropic radiator. See Figure 7.13.  
Figure 7.13 A comparison of the radiation patterns for an Isotropic Radiator (theoretical) vs. a  
Dipole (practical).  
We can look at how all other antennas emit RF energy as a comparison to our perfect  
antenna. The isotropic radiator is said to have zero antenna gain. Antenna gain is an often  
misunderstood term, so we will cover it here. Let’s start by saying that a passive antenna is  
not an amplifier and cannot increase to total RF energy being emitted or received. Having  
said that, an antenna can and does focus the RF energy in a specific direction or directions.  
This focusing of energy causes greater RF energy levels in those directions and weaker  
energy levels in the remaining areas as shown in Figure 7.13.  
We can think about this by looking at a water balloon. If we had a water balloon that was a  
perfect sphere, it would accurately represent the pattern of an isotropic radiator located in  
the balloon’s center. All of the RF energy is equally dispersed in all directions. If you  
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squeezed the balloon’s center with your hands, a corresponding bulge would appear on  
either end. The balloon is not any larger or smaller than it was, it has only changed shape.  
This is how a real world antenna works. When energy is focused in one direction, it must  
always be at the expense of energy going in another direction.  
The most basic form of real world antenna is the dipole. The dipole has 2.15 dBi of  
antenna gain over an isotropic radiator. That means there is 2.15 dB more signal in the  
direction that the energy is focused than there would be if the antenna were an isotropic  
radiator. Antenna gain is specified in one of two ways: dBi or dBd. It is very important to  
know which specification is being used when comparing antennas. dBi, as stated above, is  
referenced to the uniform radiation of an isotropic radiator. dBd, on the other hand, is  
referenced to a dipole. Most antenna manufacturers like the dBi spec because the number  
is bigger, but since there is no real world antenna that represents the 0 dB mark, many  
engineers prefer dBd. In reality, either specification is fine as long as you are comparing  
apples to apples. In the remainder of this book all antenna gain references will be in dBd,  
referenced to a dipole, unless otherwise specified.  
Important: If you need to convert from dBi to dBd, simply subtract 2.15 dB from the dBi number. If  
you need to convert from dBd to dBi, simply add 2.15 dB to the dBd number.  
There are two basic groups of antennas, omni directional and directional antennas. Omni  
directional antennas are generally low gain antennas used in the center of operational  
areas. Because the RF energy in omni directional antennas is in 360° and not in one  
specific direction, the antenna gain must always be low. The isotropic radiator and dipole  
antennas are both examples of omni directional antennas. Normally, omni directional  
antennas will be found with antenna gain less that 5 dBd. Gain in omni directional  
antennas is achieved by flattening the vertical angle of the pattern as shown in the dipole  
For proper propagation to take place, the length of an omni directional in critical. The  
theoretical minimum length for an omni directional antenna is ½ the wavelength of the RF  
carrier to be served. In many cases this ½ wave length is too long to be practical so a ¼  
wave antenna is used instead. It is extremely important to note that for a ¼ wave antenna  
to work properly, it must have a corresponding ground plane that is equal to or greater than  
the length of the antenna itself. It is for this reason that a ¼ wave antenna that works just  
fine when it is attached directly to the back of a wireless receiver has very poor coverage  
when operated at the end of a length of coaxial cable. The cable does not provide the  
necessary ground plane for proper ¼ operation as the receiver does. This is a very common  
mistake made by RF novices who are trying to improve RF performance and end up  
killing it instead!  
Directional antennas, on the other hand, seek to focus the area of coverage to something  
less than 360° to form a flashlight like coverage pattern. Directional antennas are normally  
used on the edge of a coverage area. They can have very high antenna gain factors in  
excess of 20 dBd. Normally though, in conventional wireless communications systems,  
size and cost limit directional antenna gain to less than 12 dBd.  
Directional antennas have the advantage of not only focusing the RF energy in a given  
direction, but also attenuating energy from undesired areas. This is very important for  
receive antennas in areas with high levels of RF. If positioned properly, a directional  
receive antenna can increase the desired RF energy while attenuating unwanted,  
potentially interfering RF energy from other areas. See Figure 7.14.  
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Figure 7.14 An example of a Yagi antenna.  
There are two very commonly used directional antennas in wireless communications  
systems today, Yagi and Log Periodic antennas. We will not cover the technical  
differences of these antennas here, but we will discuss the functional differences. Just as in  
omni directional antennas, directional antennas must be tuned or “cut” to a specific  
frequency range. This is all well and good when there is only one RF frequency, but if you  
are using a range of frequencies through a single antenna, it is important to ensure that all  
of the RF signals will be in the effective range of that antenna. The primary difference of  
Yagi and Log periodic antennas is the range of frequencies they can handle. Yagi antennas  
normally handle a relatively narrow range of RF frequencies, while Log Periodic antennas  
can achieve much larger effective frequency ranges.  
Figure 7.15 Telex®’s ALP-450 is an example of a Log Periodic antenna.  
On the surface it would appear the wide frequency range of the Log Periodic antenna  
would make it the obvious choice, especially when you consider that Log Periodics are  
generally also much smaller than Yagis. This however, is not always the case. Consider  
the application where there are strong off frequency interference sources (virtually all high  
RF level applications!). In these situations, the off frequency rejection of a Yagi antenna  
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can greatly improve system performance and decrease harmful interference. In general, it  
is a good idea to choose an antenna that is just wide enough to handle the desired operating  
frequencies.  
One more note on directional antennas. Because FCC rules concerning transmit power  
(Effective Radiated Power or ERP) take into account the antenna gain of the transmit  
antenna, high gain transmit antennas may not be used on transmitters in most wireless  
communications applications. The good news is that high gain antennas on the receive side  
of an RF system are also very effective for increasing system range and are commonly  
used.  
We reiterate one more important antenna concept. As stated in an earlier section, antenna  
polarization is critical to proper system operation. Transmit and receive antennas of the  
same system must be oriented in the same direction to have a proper transfer of the carrier.  
In theory, if a transmit antenna is oriented vertically, thus producing a vertically polarized  
carrier, and the corresponding receive antenna is oriented horizontally, the receive antenna  
will not be able to see the vertically polarized wave at all. In practice, there will always be  
some polarization shift in the path and the receiver will see a very small signal if it is close  
enough to the transmitter, but system range will be greatly reduced. To avoid this problem,  
antennas in a given RF system should always have similar orientation.  
Now, lets take a brief look at the role coaxial cable (transmission line, feedline) plays in  
the big picture. See Figure 7.16. Unless an antenna is attached directly to the receiver or  
transmitter in an RF system, coaxial cable is the usual means used to span the gap. The  
importance of choosing the right coaxial cable cannot be over-stressed. When choosing  
cable to use in your RF system three main factors must be considered:  
1 The cable must be properly impedance matched (correct characteristic impedance).  
Most wireless systems today are 50 ohm impedance systems. That means the final  
amplifier and filters in the transmitter, the front end of the receiver and both transmit  
and receive antennas, are designed to work using 50 ohms as the nominal impedance. It  
is extremely important to choose coaxial cable that is also 50 ohms. Coaxial cable that  
is used in video applications is normally 75 ohms, not 50 ohms. Don’t ever use video  
cable in RF transmit applications. An explanation of why this is bad is beyond the scope  
of this book, but trust me on this one, it is a bad thing, don’t do it.  
2 Consider the loss per foot of coaxial cable at your system’s operating frequency. In  
VHF systems it is usually easy to select cable with acceptable loss for runs of 100 feet  
or more. In UHF applications however, it gets a little tougher. See the coax loss chart  
below in Table 7.1. In general, it is a good idea to never have more loss in the  
transmission cable than you have antenna gain in the system. This is a good rule of  
thumb that will keep you out of trouble most of the time.  
3 Consider how the system is used. Is this a fixed installation, or a mobile one. If the  
system is being moved frequently you want to use coaxial cable that has a stranded  
center conductor. Just like other types of wire, coaxial cable with a stranded center  
conductor will tolerate being flexed repeatedly without a degradation in performance.  
However, this doesn’t mean you can tie a knot in the cable, or crimp it in a door and  
expect it to work perfectly  
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Table 7.1 Coaxial Cable Loss Chart  
Attenuation (dB per 100 feet) at the frequency given  
220 MHz  
1.8  
450MHz  
2.7  
700MHz  
3.4  
900MHz  
3.9  
Times LMR-400  
RG-8/U  
2.9  
4.5  
5.8  
6.7  
RG-213/U  
3.5  
5.2  
6.7  
8.0  
Times LMR-240  
RG-8/X  
3.7  
5.3  
6.6  
7.6  
6.0  
8.6  
10.7  
12.8  
Results are calculated and can vary.  
Figure 7.16 The typical parts of coaxial cable.  
Installation  
Having all the right gear and all the proper frequencies selected is a good first step to  
having a top notch, highly effective, wireless communications system. However, having  
the right stuff is not enough, it has to be installed properly or it is all for not. In this section  
we take the time to cover the most common do’s and don’ts of installing a wireless system  
that actually works!  
We’ll start with the general conceptual strategy for selecting a location for the RF  
equipment to live. Unlike hardwired communications systems, that can be tucked away  
almost anywhere, wireless systems must have prime real estate locations due to the  
extremely limited length of the coaxial cables that connect the transmitter and receiver to  
their respective antennas. As discussed in the previous section, the length of the antenna  
cables in a wireless system should rarely exceed 100 feet, and in some cases they should  
be kept much shorter due to frequency and cable loss. Because of this, selecting the  
location of transmitter and receiver equipment is absolutely critical to system  
performance.  
First of all, it is necessary to determine all of areas where coverage is absolutely necessary.  
These are the ‘no compromise’ areas, and your system must be designed and installed to  
consistently meet or exceed these minimum operational requirements. Anything you can  
get after these areas is gravy. Select a location for the wireless base station that is centrally  
located in the “must work” area whenever possible. Obstacles like buildings, cars, trees  
outside, walls, cameras, lighting, and equipment racks inside all act as factors to limit  
range. If they are in the direct line of site between the base station antennas and the  
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wireless beltpacks, it is important to locate the base antennas as high as possible. Getting a  
few extra feet up will often make a large difference in overall system performance.  
When installing the wireless base station it is important to avoid locating it near computer  
or other microprocessor controlled equipment. All computer type equipment radiates RF  
energy that can cause harmful interference in even the best wireless equipment. Likewise,  
your RF equipment may interfere with the operation of the computer equipment. Try not to  
have your wireless base station in the same rack as lighting controllers, audio processors or  
other highly RF radiant electronic equipment. Whenever possible, locate the wireless base  
station in its own enclosure to avoid harmful interference to or from other gear.  
The specific location of the antennas is also extremely important. Antennas should never  
be placed in close proximity to large metal surfaces that are parallel to the active element  
of the antenna. A large metal surface can cause numerous problems in most wireless  
systems. Try to locate antennas in the middle of a room (when inside) as far away from  
reflective surfaces as possible. When using omni directional antennas inside, try hanging  
them upside down with the ground plane on top, near the ceiling. This will provide the  
most effective radiation pattern. It is also a very good idea to get as much space between  
the transmit antenna and the receive antenna as is practically possible. As was covered in  
an earlier section, this will avoid the phenomenon known as desensing and increase system  
range. It is important to note that having the receive and/or transmit antennas as high up as  
practical is often more beneficial than increasing the output power of the transmitter(s).  
As covered in the previous section, it is critical to make sure that antennas are polarized  
the same on both the transmit and receive end of the wireless system. In wireless  
communications systems, the deciding factor lies with the beltpacks. Since the antennas on  
the beltpack will normally be vertically polarized it is important to ensure that the base  
station antennas are also vertically placed. Never mount an antenna using part of the  
working or active elements. Most antennas that are designed to be mounted come with  
specific mounting hardware. Trying to rig some other “innovative” mounting solution will  
almost always result in reduced system range and performance. Also, don’t paint or  
otherwise cover you antennas. Some paint has a metallic component and will greatly  
impact system performance in a negative way.  
In some extreme applications, it may be desirable to have multiple antenna locations for an  
individual wireless base station. This technique can greatly increase the effective range of  
the system if the everything is done just right. If not, it will most assuredly degrade overall  
system performance. The first thing to remember is that splitting the transmit antenna is  
never permissible! This is tantamount to setting up a frequency interference source right  
next to your operational area of coverage.  
Splitting receive antennas can sometimes be a good idea. The key thing to remember here  
is the line impedance must be properly maintained. This means you should not use a  
standard “T” connector to perform the split. The most common device used for this  
function is a Mini Circuits splitter. This device maintains the 50 ohm impedance on all  
legs. It is important to remember there is no such thing as a free lunch. Splitting antennas  
comes at a price. When you add a second antenna the signal from each antenna is reduced  
by at least 3dB. This loss then needs to be figured into the total loss/gain calculation for  
proper system performance. Multiple antenna configurations can be very challenging.  
When faced with the need to do so, it may be time to consult with an RF professional for  
help.  
As covered in the previous section, make sure you have selected a coaxial cable that is of  
the correct impedance and has a loss per foot low enough to support the length necessary  
without having more loss than you have antenna gain. Be sure to note with omni  
directional antennas, it is sometimes acceptable to have a dB or two more cable loss than  
you have antenna gain. When running RF coaxial cable, make sure the cable is not bent  
sharply as to crimp the cable. The magic of coaxial transmission lines is a direct result of  
the relationship between the center conductor, the dielectric and the shield. If a cable is  
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pinched in a door, or bent sharply around a corner, the characteristics of the cable can be  
changed dramatically and have a significant negative affect on system performance.  
Electromagnetic fields generated by other radios, AC power, arc welders or…, well you  
get the idea, can also have a negative affect on your wireless communications system.  
Avoid placing antennas near any device that has a strong electromagnetic field associated  
with it. Also, do not route antenna cables in the same runs as high voltage AC lines.  
Whenever possible, try to keep antenna cables by themselves. The thing to remember is  
the RF signal at the receive antenna of a typical wireless intercom system can be less than  
0.5µV, that’s 0.0000005 of a volt! It does not take much to disrupt such a small signal and  
anything we can do in the installation process to prevent that disruption is time well spent.  
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C H A P T E R  
8
C
HAPTER 8  
DETERMINING INTERCOM NEEDS  
DAVE RICHARDSON  
Conference Versus Point-to-Point Requirements  
As previously discussed in this book, there are at least two types of wired intercom  
systems: conference (two-wire) and point-to-point (four-wire). Although the conference  
style provides sufficient communications capabilities for some facilities, the point-to-point  
four-wire matrix offers not only functions of the conference style, but, also other  
advantageous modes. The static two-wire conference system, often seen as the back-end of  
a good matrix system, is usually comprised of belt packs, power supplies, system adapters,  
and some method of assigning channels to the ports of the matrix, such as the SAP612  
Source Assign Panel. This scenario provides the best combination of resources to cover  
most requirements of the medium to large modern broadcast facility.  
A TW intercom circuit transmits and receives audio on two wires. This format is  
conference by nature, with each station paralleled to each other. The TW system,  
originally manufactured by RTS Systems, was the first professional two-wire intercom  
to include two conference channels, call signaling, and microphone-cancel, all on three  
wires using ordinary microphone cable! Communication on a TW system may be full or  
half duplex. Operation in either of these two modes is dependent upon factors such as  
ambient noise, congestion, etc.  
Forms of communication, known as conference, party-line (PL), point-to-point (PP),  
interrupt fold back (IFB), and isolate (ISO) may be introduced by adding subsystem  
modules to the base system. The two-wire conference system, as we shall see in larger  
systems, usually requires more wiring than a digitally controlled matrix. This increase may  
be a financial and engineering consideration when choosing such a system.  
A matrix (four-wire) intercom circuit transmits audio on one pair of wires and receives on  
a second pair. This format is point-to-point by nature and can be pictured as a star  
configuration - each station connects to the center through its own multi-conductor link.  
Instead of subsystems to achieve different functions, the central processor and software  
permit the system to be dynamically configured for different forms of communication.  
Because of the digital control inherent in most modern matrix intercoms, this type of  
system usually requires much less wiring.  
Choosing either of these systems for a given facility is a blend of budget, existing wiring  
considerations, and potential intercom size. But another, less obvious reason, that studio  
control operators might prefer a two-wire intercom, in spite of wiring difficulties, is  
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subconscious panel differentiation. With a separate module used for every form of  
communication, a Directors station may have separate panels for PL, ISO, point-to point,  
and IFB control. A minimal link exists between the control stations and sub-systems. The  
link is provided by an un-switched microphone connection on the control station.  
Therefore, in the heat of a production, the director knows which panel does what, and may  
quickly access IFB to a specified talent.  
In contrast, a digital four-wire control station emulates each form of communication from  
different keys on one panel. Because panel differentiation is gone from the digital station,  
a concern for operator confusion arises. To solve the problem, the forms of  
communication can be easily be grouped into specific areas of the station panel or  
expansion panels.  
Based on wiring complexities, a two-wire intercom is often preferred for less complicated  
applications that require quick setup and teardown. A small two-wire system is easy to  
install, because it uses simply a power supply, the cable and the stations themselves. This  
configuration provides one or two channels, which is often enough.  
Figure 8.1 Wiring differences between larger conference and point-to-point styles.  
If a medium or large permanent installation is under study or system expansion is  
expected, a digital, four-wire, point-to-point system offers advantages. It inherently  
produces all forms of communications without the subsystems. The ADAM and Zeus  
matrices require minimal rack space, which is a welcome factor in tight quarters, such as  
TV mobile units.  
A static two-wire conference system can be tied to a four-wire, point-to-point matrix  
through interfaces such as the SSA324 and SSA424. It is best to avoid interfaces, if given  
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the choice, but digital interfaces, such as the SSA424, yield good intersystem  
transparency. As a result, an initial two-wire purchase can interconnect to an ADAM or  
Zeus four-wire host later without significant trans-hybrid losses.  
Fixed vs. Mobile Requirements  
A General Overview  
In the age of the portable control room, fixed and mobile requirements in larger systems  
are surprisingly similar to each other. Within television production vehicles, such as those  
used for sports and by major networks, all of the intercom forms of communication must  
be present to produce from small, to very large shows. Notwithstanding, some contrasts  
between fixed and mobile requirements could include quantities of cameras, belt packs,  
and IFBs. There are other minor differences, with the majority of them mechanical and  
weight related. For example, placing a matrix system in a truck might be better served with  
the more secure DE9 connector rather than the quick disconnect RJ12.  
In large television production vehicles, it is common to see 12 to 16 cameras covering a  
major event. This is typically more than the average television news station where three to  
six cameras would be more common. Traditionally, cameras were voltage based two-wire,  
and most of them were not directly compatible with the RTS TW intercom. A belt pack  
was used instead and connected to a SAP1026 or SAP1626 Source Assign Panel to set up  
the desired conferences.  
Along with the increase in number of cameras came the boost in IFB channels in both  
large mobile and fixed installations. Today, eight to 16 channels of IFB output in a large  
mobile vehicle are common and have matched the corresponding IFB increase in large  
fixed installations. The trend toward more IFB circuits in fixed installations has been  
fueled, of course, by the advent of the portable videotape camera and microwave links that  
permit multiple reporters to contribute to live newscasts simultaneously.  
Curiously, the requirement for vast numbers of belt packs and other two-wire devices has  
diminished slightly over the years for fixed installations and, to a lesser extent, in large  
mobile vehicles. One reason for this tendency is that camera intercoms, operating in the  
four-wire mode, can be attached directly to a digital matrix without an interface. The  
desired conference channels may be dynamically assembled in the central matrix to  
establish the required conferences.  
Also of note is that the trend toward matrix intercom for mobiles has increased over the  
last ten years when customarily, trucks would only contain two-wire intercoms with  
appropriate subsystems. The primary reason for this development is better reliability in  
matrix systems, as well as, easier reconfiguration of the intercom.  
In smaller truck systems, such as satellite and electronic news gathering (ENG) vehicles, a  
minimal intercom system is often required. These vehicles usually consist of just the  
cameraman, local director, and talent. The two forms of communication that are required  
for this kind of remote operation are conference channels and IFB circuits.  
IFB used in the ENG situation consists of both local IFB and studio director IFB with the  
local IFB downstream from the studio IFB. A system configured this way simultaneously  
allows the mobile director to communicate with the cameraman and IFB. At the same  
time, the main studio conference channel may be superimposed on the local conference net  
via either a microwave channel or a telephone interface such as the Telos Link.  
The smaller television studio can be similarly equipped. The addition of more control  
stations, a method of source assignment, and more two-wire belt packs or wireless PL  
systems is usually more than enough to provide a powerful and easily reconfigurable  
intercom for the smaller market.  
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Determining Intercom Needs, two-wire, four-wire, or both?  
In determining intercom needs for a specific application, we begin by first giving  
examples of intercom requirements. Then, we will attempt to specify an RTS intercom  
system to fill that requirement. Although specific applications are presented, we finish  
with a general discussion of how to determine whether a given system should be two-wire,  
four-wire, or some combination of each system.  
Before we begin, we should again mention that although analog two-wire conference  
intercoms continue to carry basic communications for many smaller production facilities,  
digitally controlled matrix systems offer a range of flexible alternatives. By integrating  
various forms of communications features, the four-wire matrix system for larger  
applications makes the difference between confusion and a successful production session.  
Small Studio or ENG Vehicle  
Previously, we presented the example of the ENG vehicle with its small two-wire system.  
We have also determined this application requires at least two forms of communications:  
conference and IFB  
To fill the need of a small studio or ENG vehicle, we propose the MCE325 system with its  
inherent simple IFB (meaning no tally or priority). As shown below, the MCE325 and its  
associated components make an excellent choice for this application. The powerful  
MCE325 intercom panel has the capability to produce two conference channels and two  
IFB channels, which is perfect for the electronic news gatherer. There are many other  
configurations available in the highly versatile and user programmable MCE325,  
including four-wire, vox, relays for radios, and many others.  
Note A small four-wire matrix system such as the Zeus could have been specified, but probably  
would have been overkill for this application.  
In essence, the client now has saved several thousand dollars using a small, but extremely  
versatile intercom system.  
Figure 2. The Model MCE325 provides the intercom backbone for the typical ENG  
vehicle or small studio.  
MCE325 Modular Programmable Station  
This unit is available in many physical configurations. For this application, we specify the  
MCE325-K. The ‘K’ designator includes the MCE325, MCP1 (1U rack kit), MCS325  
modular speaker, and the MCP6 removable panel microphone. The four talk buttons on  
the panel are Talk1, Talk2, IFB1, and IFB2. Talk 1 and 2 operate the two conference  
channels. The rear panel channel 1-2 connector ties to the TW5W 1x5 Splitter while its  
loop-through connects to the PS15. The channel 3-4 connector ties to the IFB325 talent  
stations. The MCE325 has a headset connector to allow the director to use the system  
privately, if desired. Other MCE325’s can be interconnected to the director’s panel. IFB  
capabilities are retained on other MCE325 panels via a special keying circuit that allows  
the slave units to operate the master unit IFB.  
PS15 Power Supply/MCP2 Rack Kit  
The PS-15 power supply and its MCP2 single component rack kit (not shown) provide  
operating power for both the BP325 programmable belt packs and IFB talent stations.  
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TW5W Splitter  
This rugged unit allows up to five BP-325’s to connect to a central location. It can be used  
outside the truck and placed directly on the ground. Using it, only one microphone cable  
needs to be connected from the truck to the cameramen, which is useful when the shoot is  
several hundred feet away. In the small studio scenario, the TW5W can be replaced with  
the TW7W 1x7 splitter mounted in the rack.  
IFB325 Talent User Station  
The IFB325 talent belt pack is worn on the talent’s belt or can be set on the ground if  
desired. It has a volume control, a XLR3 line jack, and an earset jack. A substitute for the  
IFB325 is the TT44 and TR34 wireless IFB transmitter/receiver to provide more freedom  
for the reporter, or in the case of the studio, the weather position.  
BP325 Programmable Belt Pack  
Used by the cameramen (or floor managers in the small studio), this unit features  
microphone kill, call light, and has two conference channels. It has provision for both 4  
and 5-pin dynamic binaural-headset and an additional carbon headset. A substitute can be  
the BP318 single channel belt pack.  
Headsets and Earsets (not shown)  
The PH1-R Single Muff Headset offers moderate outside noise attenuation, and allows  
ENG camera operators to use a carry-cam more efficiently. The lightweight version is the  
PH-88R for small studio use. If binaural operation is desired for the director, the PH3-R5  
Dual Muff Headset and PH44-R5 lightweight headset can be used. They offer the ability to  
maintain separate conference channels in each ear. The PH44-R5 may also be used with  
BP325 belt pack for positions such as a crane operator, who needs to communicate with  
the director, the cameraman, and hear program audio, all with separate volume controls.  
The talent earset is the model 2234, which is on-camera invisible.  
Medium Sized Studio and Mobile Intercom  
In many ways, the medium sized studio intercom is the most difficult to specify, for it is  
here we reach a thin dividing line: the extended two-wire system sometimes makes the  
most sense for such an application, until we run out fixed assets (i.e. quantities of forms of  
communications). Also, when we have more than five multi-channel, two-wire stations  
such as the RTS Model 803 or 810-CL, we should think about the four-wire matrix as a  
sensible alternative  
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We briefly touched upon the primary forms of communication used in television  
broadcast. These are PL, IFB, ISO, and PP, with the first two (PL and IFB) being the most  
important in order to produce a television program such as the news. Let’s take the  
example of the medium size system and specify first a two-wire intercom and later a four-  
wire intercom. The positional needs for our example medium studio intercom are shown in  
Table 8.1 An example of the positional needs for a typical medium sized intercom.  
Director  
Producer  
Audio  
Video  
Technical Director Tape 1  
Tape 2  
Tape 3  
Chyron 1  
Camera 3  
Teleprompter  
Talent 1  
Chyron 2  
Camera 1  
Camera 5  
Roof Access  
Talent 3  
Talent 7  
Camera 2  
Camera 6  
Telco  
Camera 4  
Floor Director  
Talent 2  
Talent 4  
Talent 8  
Talent 5  
Talent 6  
Two-wire Case (Medium Intercom)  
In Figure 3, we show a drawing of our proposed two-wire medium studio system. A  
medium mobile vehicle would be similarly equipped. It demonstrates both PL and IFB  
forms of communication.  
803-G1G5 Master Station  
In this example, we are using what we call the TW approach. Historically, TW is an  
acronym for two-wire, and has been used with reference to an RTS™ PL (conference or  
Party-Line) system for almost 25 years. We have used the model 803-G1G5 two-wire  
master stations for the more important intercom stations in the control room. This unit  
allows the operators to access up to six conference circuits in any combination with the  
additional ability to selectively listen without talking to all, some, or none of them.  
Because of the 8-channel IFB requirement, the 803 stations have been fitted with the  
G1G5 option. This option effectively moves stand-alone Model 4002 8-channel IFB  
control panel into the 803 itself, a compact, space saving feature. This G1G5 option is a  
high-end IFB system providing both tally and override with other control stations. Two  
rack units are all that is required for the full-featured 803 Master Station.  
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Figure 8.2 Figure 3. Block diagram of a medium sized intercom system using two-wire. The  
forms of communications depicted here are six conference lines and eight IFB circuits.  
862 System Interconnect  
The Model 862 System Interconnect Panel is the bridge between the Series 800 two-wire  
balanced portion and the unbalanced TW section.  
PS31 Power Supply  
The PS31 TW Power Supplies provide six powered conference channels (three each). All  
RTS power supplies contain active impedance generators to allow two-wire intercom  
audio to be superimposed on the powered channels.  
SAP1626 Source Assign Panel  
The SAP1626 Source Assignment Panel provides the TW system with its own intercom  
circuit switcher. In our particular application, the SAP1626 panel provides two functions:  
it assigns each of the 2 TW channels (stations on the right) to 1 of 12 conferences amongst  
themselves; and, it fixes each of these conferences to one of the 12-talk/listen buttons on  
the 803 stations. This provides maximum routing capability, which would be more useful  
in a mobile vehicle than in the fixed installation.  
BOP220 Connector Translation Assembly  
The BOP220 is a breakout panel that allows the TW stations to be attached to the system.  
The BOP220 (Break Out Panel, 2 Channel, 20 Jacks) connects to the SAP1626 on two  
short 25 pair ribbon cables. There are 20 positions available for user stations. Microphone  
cable or Belden 8723 is all that is required for interconnection.  
4010 IFB Central Electronics Unit  
Located in the audio room, the 4010 unit provides the logic switching and power and  
program volume adjustments for the 4030 talent user stations. One of the 4010 units  
handles the first group IFB 1-4, while the other controls the second group IFB 1-4. The  
program sources for the IFB system are introduced to the 4010 units and then fed to the  
talent stations on ordinary microphone cable.  
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4025A Splitter  
The 4025A combining device parallels up to four, 25 pair cables to yield one cable to  
connect to the 4010 IFB Central Electronics Unit.  
4030 Talent User Station  
The 4030 talent user station is a distributed amplifier with interrupt and non-interrupt  
volume controls. Studio talent personnel use a Model 2234 earset (previously described),  
which plugs into the 4030. Sports commentators wearing headphones or headsets use the  
stereo jack on the 4030. This allows IFB in one ear and a separate program feed to the  
other ear.  
MCE325-K Programmable User Station  
In our medium sized intercom, we have specified six MCE325-K units. Although  
described earlier in the small mobile unit example, these powerful stations are configured  
differently here. As you recall, we programmed the MCE325-K for two PL and two IFB  
circuits for the director. In this case, however, the panel assumes the role of a two-channel  
conference station, which contains a host of features such as individual talk/listen buttons  
and levels, footswitch control, and call light.  
BP319 Belt Pack  
The BP319 Belt Pack is a single channel, distributed amplifier (assignable to any of 12  
conference circuits via the SAP1626). It provides simple operation with its electronic talk  
switch and volume control.  
BP325 Programmable Belt Pack  
Used by the Roof Access position in our scenario, this unit was chosen for its binaural  
headset capability and high SPL, needed for a high noise area such a helipad.  
Telos Link  
This interface is a vendor unit that provides a no-fuss link to the telephone for studio-  
mobile production coordination.  
Headsets and Earsets (not shown)  
The PH-88R Lightweight Headset was chosen for the BP319 positions, the aircraft noise  
rated PH10-R5 was selected for the roof access position, and the Model 2234 talent earset  
was chosen for the news anchors because of its invisibility on camera.  
Four-wire Case (Medium Intercom)  
Referring to the position table (see Table 8.1), we now specify an equivalent four-wire  
system for our sample medium intercom. Using the four-wire matrix, we gain two more  
forms of communication, namely ISO and Point-to-Point:  
Referencing figure 3, first we notice the four-wire alternative for our medium system is  
simpler and uses less cable. Using a laptop or desktop computer (not shown), we configure  
our system as we did our application demands. In essence, we are the painters on a blank  
canvas. Attached the back end of our matrix system is a static conference line system  
linked to the Zeus matrix via four interface lines. The SAP612 provides a two-wire  
channel assignment to any of these four lines.  
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Zeus™ DSP2400 Matrix  
The Zeus Matrix is lightweight, rugged, powerful, and easy to interconnect. It also  
comes with a wonderful manual and has terrific specifications. It contains 24 ports for  
connecting to the four-wire devices. The connectors are already installed on the back plane  
of the unit. All forms of communication are integrated within the Zeus; no subsystems are  
required.  
KP96-7 Keypanel  
This master station has 15 talk keys and 15 listen keys, and it is the perfect choice for our  
application, which requires six conference channels and eight IFB circuits. Being a  
programmable unit, which can be set up differently for each position, the Video position is  
set to have 6 conference channels and 6 camera ISO channels. This allows the Video  
operator to work privately with each camera on a case-by-case basis, if required. On all of  
the KP96-7 keypanels, we add point-to-point functions between panels themselves and the  
roof access position on the remaining talk/listen keys.  
Figure 8.3 Block diagram of a medium sized intercom system using the Zeusfour-wire matrix.  
The forms of communications depicted have increased to include point-to-point and  
ISO.  
TIF-2000 Intelligent Telco Interface  
It is intelligent because it works seamlessly with the KP96-7 panels allowing the operators  
to use their keypads as telephone dialers. It also can be programmed to ring a keypanel or  
just silently tally it. This tally, or flashing alphanumeric display, continues whenever the  
telephone line has been seized, either via auto-answer by the TIF-2000 or manual answer  
by another keypanel.  
MKP4-K Modular Keypanel  
This matrix panel can be programmed just like the KP96-7. The K package designator,  
which applies to all panels in the modular series, means that a speaker, panel microphone,  
and rack kit assembly are included. The Technical Director in our scenario needs point-to-  
point capability with the Director, one IFB circuit, and two conference lines. Like all  
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matrix panels, these keys can be programmed either at the panel itself, or from the  
configuration computer (not shown) that is attached to the Zeus.  
IFB828 IFB Power Supply  
This unit is the Model 4010’s matrix brother. Since all priority, tally, and interrupt chores  
and handled by the Zeus matrix, the IFB828 acts simply as a power center for the 4030  
talent stations. There are eight of these circuits available. The program sources from the  
audio console are connected directly to the Zeus on the same ports that are used by the  
IFB828.  
SSA324 System-to-System Adapter  
The SSA324 changes a two-wire circuit to a four-wire circuit for introduction into the  
matrix. Each SSA324 is capable of two of these circuits. We have four ports in our  
scenario.  
PS15 Power Supply  
Provides operating voltage, with active impedance generator, to the BP325, BP318’s, and  
the MRT327-K.  
SAP612 Source Assign Panel  
Since a matrix typically assumes more of the traffic management role than our previous  
two-wire consoles such as the 803, less outside source assignment is required. Therefore,  
we can specify the smaller SAP612 for our application to achieve the desired circuit  
assignment. The SAP612 assigns 12 positions (TW two-wire stations) to one of six  
conference circuits. As with the larger SAP1626, the SAP612 in our system does two  
things: it assigns each of the 2 TW channels to 1 of 6 conferences amongst themselves, and  
it fixes each of these conferences to up to 4-talk/listen keys on the matrix stations.  
MRT327-K Modular User Station  
The MRT327-K was chosen for the Chyron positions in our medium system for its  
simplicity. These stations are capable of two-channel operation, one channel at a time.  
PAP951 Program Assign Panel and UIO256 GPI  
These ancillary devices attach to a special connector on the matrix. No extra ports are  
required, preserving the maximum size of the matrix. Meaning, more of these units can be  
added to the system. The PAP951, located in the Audio position, allows the operator to  
quickly assign programs to IFB circuits. The unit attaches to the matrix on a digital pair,  
and no actual audio flows through this controller device.  
The UIO256 is a 16x16 General Purpose Interface unit. It is included in our intercom for  
keying a two-way radio in future expansion of the system. If a squelch relay contact  
closure is available from the radio, the UIO256 can cause a flashing tally to appear at any  
given matrix keypanel when there is activity on the radio.  
Cameras in the Medium Intercom  
If the cameras can be set to four-wire intercom operation, they can be tied directly to the  
matrix. They may be established as any number of conferences. Operating in this manner  
gains the advantage of camera ISO ability from any matrix station (on the left side in  
figure 4). Also, the audio levels to and from the cameras can be set internally within the  
matrix. No extra outside audio amplifiers are necessary. The reason for this is the RTS  
Zeus is a mixer, not just a matrix of physical crosspoints like those we had in the past.  
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Large Studio or Mobile Vehicle  
Before the advent of the digitally controlled matrix system, large intercom systems were  
cumbersome to specify. The engineer had to know precisely how many forms of  
communication to obtain for the system. Any increase in these after the initial sale would  
mean major physical changes in equipment. Also, to accommodate the special needs of  
customers, manufacturers were driven to produce special, one of a kind intercoms that  
were difficult to test, install, and provide support.  
The arrival of the first digitally controlled four-wire matrix systems changed customers  
thinking. Wary at first, because of early reliability problems, customers were slowly  
purchasing matrix systems to test the waters. The arrival of the ADAM system in the  
late 1990’s brought many welcome changes. The most important of these were two  
enhancements: the ability to change individual audio levels at the stations, and matrix  
linear expansion, instead of logarithmic expansion, which effectively lowered the price of  
systems (which previously cost thousands of dollars more).  
To determine the needs for a large intercom system is, in many ways, easier than of the  
small and medium systems. First, we assume a four-wire matrix will most likely be a  
better choice for such an application than an extended two-wire system. The ADAM  
136x136 expandable matrix and its small cousin ADAM -CS 64x64 make excellent  
choices for these larger systems.  
Figure 8.4 Figure 5. Block diagram of a large size intercom system using a twin ADAM™  
configured as a 200x200 matrix.  
In very general terms, we only need to know two things to get into the ballpark when we  
specify the equipment list: the size of the matrix; and, the type of keypanels in each  
location. We cover that exact process the next section, but for now let’s look at a typical  
large system.  
After we determine the specific needs of the control rooms and studios in the figure 5, we  
duplicate these areas to get the total equipment count. A large two-wire system like our  
sample, would leave us facing such issues such as excessive cabling, mixing loses,  
routing, and a host of other problems. Working with a digitally controlled matrix makes a  
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large design effortless. Apparent in our sample system is the ADAM here is a storehouse  
for 10 separate intercom systems! These internal intercom systems are configured to work  
separately or concurrently with each other. With the new automated server feature in AZ-  
Edit, files can be downloaded without human intervention by the powerful new UPL (User  
Programmable Language). This set of useful Boolean algebra expressions allows an  
almost endless chain of events to be introduced to the system to solve any problem. In  
short, the days of custom intercoms are over.  
Determining the Makeup of the Intercom Matrix  
First Step--Determine the Size  
The matrix is composed of audio in/out ports (four-wire). These are further classified as  
panel ports (6 wire) and non-panel ports (four-wire). A non-panel port is simply a regular  
port without the data lines tied to the matrix leaving only the four-wire audio in and audio  
out. A typical broadcast intercom system consists of Users, IFB Circuits, Cameras, and  
Miscellaneous ports (to include static Party-Line systems, 2-way radios, telephones, etc.).  
The first step is to determine the size of the central matrix by counting everything that is  
attached it. We will use our large sample for this exercise.  
Users  
The users of the matrix are operators with keypanels. Going down the list of stations  
(derived from a source-destination table, block diagram, or position list), we count them  
one by one. In figure 5, we have 10 keypanels x 6 large control rooms plus 1 keypanel x 4  
small control rooms. Thus, in this example, we have a total 64 users. The 64 users narrow  
our deciding matrix down to either an ADAM or ADAM -CS (barely) depending on  
subsequent port counts. A Zeus (24x24) would definitely be too small.  
IFB Circuits  
The next port count we need to add is the number of IFB circuits. All RTS matrices have  
the unique ability to use a port delegated for IFB in a split fashion. What this means is a  
port counted for IFB automatically yields an input port for the program feed from the  
audio console. Therefore, program sources do not typically become a factor in the count  
unless there are more of them than IFB circuits. The situation is rare, though.  
The IFB circuit, used in virtually all television facilities, is usually a one direction audio  
cue to on-air talent. The signal interrupts a predefined audio source, such as program  
audio, to inject a directive from the director, producer or audio. In its simplest form, IFB  
uses an earpiece, an external headphone box (to permit the talent to control the audio  
foldback level), a program source and a control station. A common IFB application is the  
live TV newscast where a director wishes to advise the talent a cut-in is starting.  
Since all routing of the programs to IFBs is performed outside the matrix in our example,  
no large matrix assignment panel, such as the LCP102 (64x64 switcher) or PAP950-50  
(50x50 switcher), is required. Unlike the PAP951 and PAP952, these panels sometimes  
find use in larger systems because of their ability to switch to any part of the matrix and  
thus, not fixed to any section.  
With the influx of ENG vehicles, many of today’s IFB circuits are telephone dial-in. These  
particular circuits are sometimes left out of the count for various reasons. Including all IFB  
circuits not only insures correct matrix size, but also helps specify ancillary equipment  
such as the program assignment panel as described above.  
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In our large intercom system, we find 4 IFB x 6 large control rooms plus 4 IFB x 4 small  
control rooms. This makes our IFB count 40, which brings our total count so far to 100.  
This means we cannot use an ADAM -CS 64x64 for this application.  
Cameras  
Most high-end cameras are capable of operating in the four-wire intercom mode. In our  
sample large intercom system, the engineering staff has chosen the best cameras available  
and purchased a great quantity of them. Continuing our count of points in the system, we  
find 6 cameras x 6 large studios plus 3 cameras x 4 small studios. The total number of  
cameras is 48. This makes our total count so far 148, which means our ADAM will consist  
of at least a twin frame combination using bus expanders to connect two matrices together.  
Each frame alone is capable of 136.  
Miscellaneous  
Static Party-Lines  
On the back end of our matrix, we find a number of belt pack rings. As discussed earlier,  
these static Party-Lines (2 in each studio) are fixed to dynamic Party-Lines (created by the  
matrix amongst panels). Under the AZ™-Edit configuration program, the static Party-Line  
is set as permanent talker and listener on the dynamic PL. Since each static Party-Line  
must be counted as a port, we find 20 in our large system (2 PL’s x 6 large studios and 2  
PL’s x 4 small studios) bringing our total matrix count to 168.  
Wireless Intercom  
In each studio, we have added a wireless intercom to consist of a BTR300 base and two  
TR300 transceivers. Each of these is counted as one port. There are 10 studios total, so our  
matrix count is now 178.  
Telephones  
We have three telco lines for each of the large studios, two for production coordination  
(TIF951) and one provided by a vender for talent dial-in and other general use. Our total  
telephone circuits are 18, (3 telco’s x 6 large studios). Our matrix total now stands at 188.  
Studio Announce and Dressing Room Paging  
We have one stage announce amplifier and one dressing room page amplifier in each large  
studio. That is 2 amplifiers x 6 large studios equals 12. This brings our total matrix count  
to 200.  
Second Step--Determine the Panels  
Now that we have found the matrix size (200x200) for our large application, it is time to  
establish the type of keypanel to specify for each of the control positions. The RTS  
matrix intercom product line has almost 25 different panels from which to choose, from  
four keys to 64. Generally, we are interested in the quantity of these keys that are needed  
for each control position. These keys (talk and listen on each panel) are programmed to  
emulate the four forms of communications. Discussions with operators might be of help in  
determining the type of intercom console to assist them in performing their jobs.  
In our large system scenario, we find two styles of matrix panels are more than enough to  
fulfill the needs of all 10 positions in each large studio and the director/producer position  
in the small studios.  
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KP96-7 Keypanel  
The KP96-7 matrix intercom panel has 15 talk and 15 listen keys with alphanumeric  
displays. This is a perfect quantity for the Director and Producer positions. In the large  
control rooms, we have added the EKP96-8 Expansion Panel to these positions which  
gives us an additional 16 talk and 16 listen keys with alphanumeric displays. These extra  
keys are used for the IFB circuits. We have specified these panels, instead of the new  
KP32 (32 Talk and Listen Keys, 2U), because of the customer’s desire for panel  
differentiation between the IFB circuits and the other forms of communications (PL, ISO,  
and PP) that will be programmed into the main KP96-7 panels.  
KP96-6 Keypanel  
All other positions in the large control rooms will have the KP96-6 keypanel. This unit has  
seven talk and seven listen keys with alphanumeric displays. Most of the RTS matrix  
keypanels have the ability to adjust individual volumes of the point-to-point and  
conference lines.  
Other Considerations in Determining Intercom Needs  
Physical Constraints  
In mobile and fixed applications, there are times when the client does not have the luxury  
to choose a given panel because there is not enough room to mount the panel. We will  
cover alternative panels and other devices that can be substituted for both two-wire and  
four-wire systems.  
two-wire Conference Systems  
For rack mount speaker stations, consider using the MRT327-K (1U) rather than the older  
RMS300 (2U). You will gain call light ability with the MRT327, a removable panel  
microphone, and a speaker that sounds great despite its small size.  
In a tight fit, when using multi-channel master stations, the 810-CL may be substituted for  
the model 803 Master Station. While not possessing all the features of the 803, this  
compact 1U station still features 10 conferences.  
In the central equipment rack, when considering a SAP1626 Source Assignment Panel to  
add to an 803 system, you may consider the 4012 Break Out Panel instead. Though the  
ability to quickly assign conference channels is lost, you will gain 6U in space. The reason  
for this is that the 862 and SAP1626 are eliminated from your system, and the 4012  
mounts in the back of the rack. Conferences are set to 803 buttons by connecting the TW  
XLR3 cable to one of 12 jacks that determines the button assignment (1-12).  
Four-Wire Point-to Point Systems  
The Zeus matrix may be specified if the port count is 24x24 or less. It is lightweight,  
only 2U high, and all the connectors are on the back.  
In a tight area where a 2U matrix intercom panel such as the KP96-7 (15T/15L) has been  
specified, a substitute could be the KP12. The KP12 (2U) has 12 keys, alphanumeric  
displays, speaker, and optional panel microphone. If a KP96-6 (7T/7L) has been specified,  
the substitute in this case might be the MKP4-K. This 1U panel has four keys,  
alphanumeric display for the call waiting window, panel microphone, and speaker.  
In the case where a high-end station such as the KP96-7 with EKP96-8 expansion (4U  
total) is earmarked, a KP32 keypanel (2U) could be specified gaining 2U of rack space.  
This is particularly valuable in the large mobile situation.  
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How old is Too Old?  
Should you completely replace your existing system? Probably not! The RTS TW  
system has been around for a long time. As such, there are products that have been in  
constant service for 20-25 years. The good news is the newer two-wire conference  
products are completely compatible with the older two-wire products, as long as the older  
units are Phase 3. Phase 3 (circa 1979) means that operating power is required on only one  
channel, not both. Adding a source assignment panel and more user stations can be done  
rather easily as long as the existing power supply (a PS10 or PS50) can handle the  
increased capacity. Even an 803 system can be added to an old system with little or no  
modification, as well as the addition of a front-end matrix to the older system.  
In the case of older matrix systems, such as those currently in use worldwide, existing  
keypanels can be used with a new system. Even those panels used as far back as the  
CS9400+ disk based system, can be used with a new ADAM matrix with a little  
modification.  
Expandability  
As discussed earlier, one of problems with the extended medium and larger two-wire  
conference systems is you will need to know precisely what you need in advance of the  
purchase. This is more apparent when specifying IFB, ISO, and Point-to-Point forms of  
communications. If you have purchased the 4001 4-channel IFB system, you will find  
yourself in a bit of a pickle the day you need six IFBs! In the case of conference channels,  
you can certainly add more belt packs or master stations without much of a problem. This  
is because the RTS TW system is a current based system rather than a voltage based  
one. All TW stations exhibit high impedance to the line, and hence, do not load it down.  
In terms of the matrix systems and their expandability, it depends on the application. A  
Zeus matrix is expandable up to a 24x24, and indeed comes with the maximum 24 ports.  
Therefore, additional panels or other devices can simply be added without having to do  
anything to the frame. The ADAM™-CS can be ordered in groups of eight ports to a  
maximum of 64. It is a good choice for medium applications where a Zeus might work  
initially, but expansion is foreseen. Finally, the standard ADAM can be used in larger  
applications from 8x8 to 136x136 and beyond via frame expansion.  
Interoperability  
One of the key things to consider in determining intercom needs is when a television  
station is owned by a network or has a mobile vehicle already with an RTS matrix.  
Additionally, if there is a need for trunking to other intercom systems, which are of the  
ADAM or Series 9000 vintage, a similar system should be specified. With trunking, as  
described in other sections of this book, up to 20 intercom systems can work intelligently  
with each other, as if they were one very large system. This sets up the ability to use the  
scroll list on a given matrix keypanel to access the Director in another intercom system,  
either locally or halfway around the world.  
Maintenance  
Less is more, so they say, and so it is with the intercom (i.e. less wiring the better). In the  
age of the digital matrix, even with its fewer wires, comes another welcome arrival, AZ-  
Edit. Virtually, anything regarding the health of the system may be determined through  
this intuitive program. Gone are the days of troubleshooting audio because any keypanel  
can produce a tone to follow. The crosspoint screen can be displayed to show why people  
are hearing at any given point. You can even show what keys are activated on a miniature  
keypanel at the configuration terminal. Recent advances also include software upgrades to  
keypanels and matrix via active download, audio level control, and other interesting  
features.  
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Keypanels in RTS matrix systems do not store configurations. Therefore, if a panel  
needs to be replaced at any location, the new panel will assume the identity of the old one.  
On the matrix, there are diagnostic LEDs on the hardware that show if there is a problem  
or fault.  
Budget  
Getting back to reality, budget is always the determining factor whether you will purchase  
a two-wire, four-wire, or some combination of both. Generally, if your budget is limited,  
you can start with a small two-wire system with idea of making this system the back end of  
a future matrix system. Tailoring a purchase in this way takes a bit of doing, because of the  
increased level of planning that must be done. Telex Communications, Inc will work with  
you to help you in this early stage of equipment specification. Whatever your decision,  
you will have a new system that works flawlessly and becomes an invisible part of your  
work life.  
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CHAPTER 0  
CHAPTER 0  
CHAPTER 0  
C
HAPTER 0  
GLOSSARY  
A
Acoustics The science of sound.  
Acoustical A term used to differentiate a sound signal from its electrical signal counterpart or representation.  
For example: A microphone converts an acoustical signal (from music or speech) to an electrical  
signal. A loudspeaker converts an electrical signal to an acoustical signal.  
Active Devices Devices requiring operating power (battery or other) in addition to the signal. Examples are  
transistors, integrated circuits, amplifiers, and intercoms.  
AF Audio Frequency. Within the range of 20 hertz to 20,000 hertz.  
AGC Automatic Gain Control.  
All Call For talk key assignment only. Activating an All Call key will also activate all talk keys to the left  
of the All Call key (up to, but not including another All Call key).  
Alpha Alphas are the user-changeable names which identify destinations (intercom ports, Party-Lines,  
etc.). Change Alpha names for intercom ports using the Port Alpha button in AZ™EDIT Change  
Alpha names for everything else using the Other Alpha button. When you assign a destination to  
a talk key, the alpha name will appear in the alphanumeric display for that key (on keypanels so  
equipped).  
AM Amplitude Modulation.  
Ambient Conditions existing at a location. Example: ambient temperature.  
Ambience Background noise or sounds.  
Ampere The amount of electrical current when one volt is applied to one ohm. Also equal to one coulomb  
of electrical charge passing a point in one second.  
Amplitude The size of analog electrical signal as opposed to its frequency or other parameters. Magnitude  
also indicates a size. Amplitudes focus more from the measurement viewpoint, for example: a one  
volt peak sine wave amplitude, a one volt average amplitude.  
Amplifier Usually an electronic device that increases the amplitude of an electrical signal. Examples include  
a microphone preamplifier that brings millivolt signals to volt levels. A power amplifier that  
makes a one milliwatt signal into a 10, 100, 1000, or more watt signal.  
Analog vs. Analog (as opposed to digital) here refers to the way information is put onto an electrical signal.  
Digital  
An analog signal varies in voltage or current in step with the signal it represents. In the case of the  
acoustic pressure wave from speech, the pressure wave is converted to an electrical signal by a  
microphone. The voltage from the microphone varies as the sound pressure from the acoustic  
wave. A digital electrical signal either represents a binary number 0 or binary number 1.  
Combinations of numbers represent the amplitude of the pressure wave. The pressure wave is  
sampled at a rate two or more times the highest frequency to be transmitted. Therefore, there are a  
sequence of digital numbers representing the speech over a period of time. The advantage of  
analog circuitry is that it is conceptually simple and relatively easy to create. The disadvantage of  
analog circuitry is that it is sensitive to distortion and the quality of the circuit design and  
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fabrication must be very high. Advantages of digital circuitry include 1. Frequency response, and  
distortion are constant and independent of the circuitry (either it works or doesn’t, the circuitry  
doesn’t change the frequency response or distortion). 2. Physical aging, wear, and tear have little  
effect on the quality of the signal. 3. The circuit design and fabrication are very straightforward.  
The disadvantages of digital are that a substantial investment in system / circuit design must be  
made, the circuitry tends to produce and radiate interfering signals, more circuitry than analog is  
required in small units.  
Attenuation The decrease in magnitude of a wave as it passes through a transmitting medium (including air,  
cables, circuitry). Attenuation is also used to indicate a numerical value of the attenuation through  
an electrical attenuator, for example: a 10 decibel attenuator (or “pad”).  
Attenuator A device, usually passive, that decreases the amplitude of an electrical signal. For example: to  
(Loss Pad)  
prevent the overload of a sensitive microphone input when the signal is much larger than a  
microphone signal.  
Audio 1. A term used to describe sounds within the frequency range of human hearing. Also used to  
describe devices that are designed to process signals generated from audio (acoustic) energy or to  
be used to generate audio (acoustic) energy. 2. In television, the sound portion of the program.  
Audio Range of frequencies lying within the range of human hearing, often 20 hertz to 20,000 hertz,  
Frequency  
where hertz is cycles per second.  
Auto Follow A key assignment for listen keys only. Auto follow causes a key's listen assignment to always be  
(AF)  
the same as the talk assignment. Thus, if you change the talk assignment, you do not also have to  
change the listen assignment. You can manually activate an auto-follow listen key independently  
of the talk key. If you want auto-activation (or deactivation) of listen during talk, use one of the  
other auto key assignments, such as auto listen or auto mute.  
Auto Functions Auto functions are special key assignments that work with other key assignments. For further  
information, see the glossary descriptions of individual auto functions: auto-follow, auto-listen,  
auto-reciprocal, auto-mute, auto-table, all-call, DIM.  
Auto Listen (AL) A key assignment for listen keys only. This assignment works like auto follow, except that listen  
automatically activates during talk, Auto listen is sometimes a good assignment for use with  
Party-Lines or other non-keypanel devices that do not have talk-back control of matrix  
crosspoints.  
Auto Mute (AM) A key assignment for listen keys only. This assignment works like auto follow, except that listen  
automatically mutes during talk. Auto mute can help prevent feedback or echo when talking to  
certain destinations. In some cases, you may find it works better to disable talk latching for this  
type of key, because if you accidentally leave talk latched on you will never be able to hear the  
destination. To disable latching, in the Keypanels / Ports menu of AZ™EDIT, check the “D”  
check box for any talk key that has auto mute selected as the listen assignment.  
Auto Reciprocal A key assignment for listen keys only. This assignment forces you to continuously listen to  
(AR)  
whatever is assigned to the talk key. It is used commonly on keypanels which are not equipped  
with listen keys, to allow listening to Party-Lines. It is also useful to force listening when it is  
desirable to have an operator continuously hear a Party-Line or other source.  
Auto Table (AT) A key assignment for listen keys only, when the corresponding talk key is assigned to an IFB.  
Auto Table causes a listen key's assignment to always be the same as the Listen Source for  
whatever IFB is currently assigned to the talk key. (You define the Listen Source in AZ™EDIT  
during IFB setup.) Auto Table is convenient in a broadcast environment when a director needs 2-  
way communication with the IFB talent, AND the IFB keys are frequently reassigned during the  
course of a program to talk to new talent locations. Using AZ™EDIT, several IFBs can be set up  
in advance, and their Listen Sources can also be defined during setup. Then every time an IFB  
talk key is reassigned on a keypanel, the Listen Source for each new IFB will automatically  
become the listen key assignment for that key. For further information about Auto Tables, Listen  
Sources, and IFBs, search for “IFB” in AZ™EDIT help.  
AWG American Wire Gage. For example: the AWG wire size recommended by RTS™ Systems for  
intercom wiring is 22 gage.  
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B
Balanced line A balanced two conductor line carries audio that is differentially driven and balanced to ground.  
Neither conductor is tied to circuit common. Circuit common is either tied to a transformer center  
tap, or is an electrical center point, or not tied at all. The signal (with respect to ground) on one  
conductor is equal and 180° out of phase with the other conductor. Balance Adjustment or  
Control In stereo audio, an adjustment to balance the left channel versus right channel. At RTS™  
Systems a name given to the null adjustment control. The null adjustment or balance control is  
used in two lines of products: user stations and interfaces — two to four-wire interfaces and two-  
wire to two-wire interfaces. In the headset user stations the balance control (called sidetone in this  
case) is adjusted until the side tone heard in a headset is optimum. In a speaker user station, the  
control is adjusted for the best null so that a full duplex conversation can be held with both the  
panel microphone and loudspeaker enabled at the same time (without feedback).  
Bathtub Curve A curve showing failure rate versus elapsed time. Typically this curve is bathtub shaped. Initially  
a high failure rate occurs when active and passive parts fail (“infant mortality”). The parts fail  
under initial turn-on and burn-in stress. The flat part of the curve is the normal life of the  
equipment. The curve rises again when the equipment ages and is in the wear-out part of its life.  
Inspecting parts before they are used reduces the initial failure rate. Using higher quality  
components and proper derating of components in the equipment design, lengthens the equipment  
operating life. RTS™ Systems burns-in power supplies and other equipment to catch early  
failures before the equipment goes to the end user.  
Bel Originally a unit of measurement that meant that a sound was twice as loud. A more convenient  
unit for other reasons is a decibel, which is a tenth of a bel. Therefore an increase of 10 decibels is  
twice as loud (and a decrease of 10 decibels is half as loud). Mathematically a unit that represents  
the logarithm of the ratio of two powers. See also decibel.  
Beltpack Portable headset user station. This station is designed to be worn on a user’s belt, but is also  
fastened to the underside of consoles, taped to a structure near the user, or mounted on a piece of  
equipment.  
Binaural 1. A special process of using an artificial head and two microphones to closely emulate the spatial  
and frequency hearing of a human. 2. Two earphones, two signals, may be stereo or may be two  
different signals.  
Biscuit A portable speaker station.  
Bit Binary Digit. One eighth of a byte. One eighth of a dollar.  
Block Diagram / A diagram to show the basic concepts of a device or system. Often the block diagram has system  
Single Line  
parameters such as transfer functions, gain, loss, level, DC voltage, inputs, outputs, and so on. I.)  
Block Diagrams are used on the Product Data Sheet to clarify the functions, show performance  
Diagram  
capabilities, and to show the input, output, control, and interconnection points. This diagram also  
defines and clarifies the specifications called out on the data sheet. II.) The diagrams called Block  
Diagrams are often, in fact, “Single Line Diagrams”. Single Line Diagrams are similar to the  
Block Diagrams but show more detail such as number of conductors in a cable, connector  
designations, connector details such as male/female, Equipment Model Numbers, and Equipment  
Designation Names/Numbers. At RTS™ Systems, these single line diagrams are called “System  
Block Diagrams” and are used for several purposes: 1. Act as a check list against the customer  
requirements. 2. Demonstrate to the customer the meeting of the customer’s requirements. 3. Are  
used to develop the equipment list (Lists the Quantities and Models numbers of equipment  
required to make the system). 4. Provide the information necessary to perform a system test. 5.  
Provide information to estimate wire and cable requirements. 6. Provide information to aid  
installation at the customer site. (Wiring Diagrams and Wire List can be generated from this  
information). 7. Graphically give a measure of the size and complexity of a given  
communications system. 8. Provide a means of troubleshooting system problems during  
commissioning, during operation, and during maintenance. 9. Provide a documentation basis to  
expand the system in the future. 10. Provide documentation for telephone support of the customer  
from the factory.  
Blocking A communication system blocks a requested call or access usually by a busy signal.  
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Bridging Bridging impedance means an impedance that when paralleled with a nominal impedance will  
have an non-significant effect on a circuit. For example: for a nominal impedance of 600 ohms, a  
parallel impedance of 3,000 ohms (5 times) would make the net impedance 500 ohms, 17 percent  
less than 600 ohms or 1.6 dB. A parallel impedance of 6000 ohms (10 times) would cause about a  
9 percent change or about a 0.82 dB difference. A parallel impedance of 12,000 ohms (20 times)  
results in about a 3 percent change or 0.26 dB. In present day audio systems, line level and power  
amplifiers have input impedances specified at 600 ohms or 15,000 ohms. Microphone  
preamplifiers are usually ten times the expected source impedances. For example: for 150 ohm  
microphones the input impedance is 1,500 ohms or greater. Earlier RTS™ Systems intercoms  
also had this microphone input value, but a compromise value of 470 ohms was necessary  
because of the crosstalk in headset cords. However, RTS™ Systems professional audio  
equipment generally adheres to current audio standards.  
BW Bandwidth.  
Byte Eight binary digits or bits.  
C
Call light A feature in intercoms that is used for two different purposes: 1) To get a user to put his headset  
back on (blinking call light). This method is the standard way for RTS™ Systems equipment. 2)  
To generate a cue (steady call light). The usage in this case is often as follows: light on means  
standby, light off after light on means execute. This method is used by other manufacturers and IS  
optional with RTS™ Systems equipment. In some user stations, the call light feature is standard  
(BP325, MCE325), in other stations, it is an option.  
Capacitance The ability to store electrical charge between two conductors. Measured in farads (Named after  
Michael Faraday). A capacitance value of one farad can store one coulomb of charge at one volt.  
One farad permits one ampere of current when the voltage changes at the rate of one volt per  
second. Typical sizes are measured in: millifarad one-thousandth of a farad microfarad one-  
millionth of a farad nanofarad one-thousandth of a millionth of a farad picofarad one-millionth of  
a millionth of a farad.  
Capacitive The opposition to alternating current through a capacitor. Capacitive reactance, Xc is measured in  
Reactance  
ohms and is equal to: 1 / [2 * π * frequency * capacitance].  
Capacitor Two conducting surfaces separated by a dielectric. The dielectric could be a material, air, or a  
vacuum. The capacitance of the capacitor is a function of the area of the surfaces, dielectric, and  
spacing between the conducting surfaces.  
Cardioid Pick- The pick-up pattern of a directional microphone is frequently of cardioid (heart) shape. The  
up Pattern  
maximum cancellation (minimum pick-up) occurs at an angle of 180°. The sound power  
concentration is approximately three times.  
CCU Camera Control Unit. Usually located in an equipment room (studio) or a bay in a mobile truck  
(mobile). The CCU is connected to the camera “Camera Head” via a cable. The cable is either  
wire “multicore,” triaxial cable “triax,” or coaxial cable “coax.”  
Channels and Channels and Buses are pathways for signals to travel. There are more than one channel or bus to  
Buses  
allow for multiple conversations or information flows to occur simultaneously. Multiple buses  
separate signals using space and the process is sometimes called space multiplexing.  
Analog Channels and Buses In the discussions here, analog Channels or buses carry signals  
representing audio. There is an exception, the call light signal is superimposed over the signals  
representing audio. This signal is not heard by humans because of its 20.0 kilohertz frequency. In  
this case the voice audio and the call light signal are multiplexed using frequency separation. The  
words “channels” and “buses” are often used interchangeably. In a twelve channel or bus system,  
it is possible for a user station to be tied to say system bus 5 and system bus 3 when the user  
station channel selector switch reads 1 and 2 respectively. For purposes of distinction, discussions  
that talk about system channels or buses and user station channels, the word bus will refer to  
system buses and the word channel will refer to user station channels.  
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Digital Buses In the microprocessor units, addresses and data are moved on digital data buses.  
These buses vary in width from three to 16 bits. Some buses are bi-directional and the logic  
transmitting and receiving data on these buses is usually of the “three state” variety. Data is  
multiplexed on these buses using time division or separation.  
Characteristic The Characteristic Sound Pressure Level of a headphone is the sound pressure level that an  
Sound Pressure  
electrical output of 1 milliwatt generates.  
Level  
Circuit 1. A complete path for electrical power or an electrical signal (usually two conductors). 2. In a  
system, a channel for one or two way conversation may be called a circuit.  
Circumaural A headset where the earpieces surround the ear usually providing some isolation of outside noises  
Headset  
from the ear.  
Clipping A type of distortion resulting from overdriving an amplifier.  
Close-Up Found in a pressure gradient microphone, this effect causes strong low frequency pickup at near  
Effects  
distances.  
Coil Effect The inductance exhibited by a spiral-wrap shield at audio frequencies.  
.Communicatio The audio signal from any input port can be routed to any output port. For example: during  
n between Ports  
(Point-to-Point,  
keypanel setup, you assign keypanel keys so that keypanel operators can talk and listen to other  
intercom ports. Communication of this type is called point-to-point communication. You can also  
route signals between intercom ports without keypanels. One way to do this is to force crosspoints  
or P-P)  
in the Crosspoint Status screen of AZ™EDIT. Another way to do it is with a GPI input.  
Compression Headset wearing comfort is affected by weight and the force of the earpieces on the head. This  
Force  
“compression force” is measured in newtons, N. One newton is about the weight exhibited by a  
mass of 100 grams.  
Condenser A microphone using a capacitor as the sound pressure sensing element. Condenser microphones  
Microphone  
require a polarizing voltage. Condenser microphones outputs are high impedance and need to be  
buffered by an active device. The active device(s) needs power, so various phantom and A-B  
powering schemes are used to buffer the active device(s).  
Conductivity The ease by which a material will support an electrical current. Mathematically the reciprocal of  
resistivity.  
Conductor A material that will support an electrical current.  
Conference A conference system allows a group of people to intercommunicate. For example, one person can  
Intercom  
Systems,  
Conference Line  
Intercom  
Systems, Party-  
talk and all the others on the bus or channel can hear. When the system is full duplex, anyone can  
talk and the rest can hear or interrupt the speaker at any time. The conference and distributed  
matrix systems presently sold by RTS™ Systems are full duplex and are non-blocking, which  
means that access to the channel is immediate and there is no busy signal. Conversations on  
Line (PL) conference systems are in general, non-private. A conference system can be two-wire or four-  
Systems  
wire. RTS™ Systems sells both two- and four- wire conference systems. The two-wire  
conference system (RTS™ Systems “TW” system) is simple, economical, and very convenient to  
use. The four-wire conference system performs as well as the two-wire system, is easier to  
interface to other systems, but requires more equipment and is more costly. Conference systems  
can be distributed or centralized. Most of the systems that RTS™ Systems makes are distributed  
conference systems. Distributed means that a station can be plugged-in at any arbitrary point  
along the bus or channel. Centralized means that all stations are tied to a central point where the  
conferencing function is actually accomplished. Note: Sometimes the conference intercom  
system is called an interphone or headphone / headset system.  
Control Room A room, usually adjacent to a studio, where the production is controlled by the producer, director,  
technical director, (and sometimes the audio mixer, lighting director, assistant director,  
production assistant, and Chyron operator). In remote pickups the control room is in the mobile  
unit, which may be several kilometers from the televised action.  
Coupling with Basically differentiation between ear-pieces that are worn on the auricle (supra aural headsets),  
the Ear  
and those that envelop the auricle (circumaural headsets).  
CPS Cycles Per Second. Obsolete designation replaced by Hertz (Hz).  
Crosspoint The term “Crosspoint,” like the term “Matrix” is inherited from intercom systems, such as the  
RTS™ CS9500, CS9600, and CS9700, that use a switching matrix to route intercom audio. In  
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those systems, the crosspoints are the actual switches that close or open to connect or disconnect  
talk and listen paths. RTS™ ADAM™, ADAM™ CS, and Zeus™ Intercom Systems do not  
actually use crosspoint switches, but use a technique called time division multiplexing (TDM), in  
which communications are routed as digital packets. However, use of the term “crosspoint”  
persists since packet routing basically accomplishes the same thing as conventional crosspoints:  
namely, connecting distinct talkers and listeners. In this sense, a crosspoint can be thought of  
simply as a communication link between any two points in the intercom system.  
Crosstalk Interference caused by audio energy from one line coupling (“leaking”) into adjacent or nearby  
lines.  
Current A current is a flow of electrons past a point in a circuit and is measured in amperes (coulombs per  
second). Practical currents in electronics are measured in: amperes, milliamperes one-thousandth  
of an ampere, microamperes one-millionth of an ampere, nanoamperes one-thousandth of one  
millionth of an ampere, picoamperes one-millionth of a millionth of an ampere, femtoamperes  
one-thousandth of a picoampere  
Current Sources RTS™ Systems uses “Current Source” technology in many of its communications products. This  
technology allows the summing of signals on a single pair of conductors across a single system  
bus termination. This allows a distributed conference line system. Stations can be added  
arbitrarily anyplace in the system. The system allows two to 75 stations to be put on the system  
with only a maximum level difference of six decibels. The current source allows a signal to be put  
on the bus without shorting out the other signals.  
D
Daisy Chain Some TW user stations allow the stringing together (or daisy chaining) of user stations. These  
stations have a “loop through” or “extension” connector as well as a ‘line” or “line input”  
connector. Connecting up a TW system by connecting one user station to another via the line and  
loop through or “ext” connectors. This is as opposed to “home running,” which is running a cable  
from each user station to a central point (“home”).  
dB Decibel, see definition for decibel.  
dBm A reference level where 0 dBm equals 1 milliwatt. In a 600 ohm system 1 milliwatt corresponds  
to a voltage of 0.775 volts.  
dBu A reference level where 0 dBu equals the voltage as a dBm (0.775 volts) but without the 600  
ohms in the circuit.  
DC Direct Current. Example: current as from a battery.  
decibel (dB) 1. One-tenth of a bel. It is equal to 10 times the logarithm of the power ratio, 20 times the log of  
the ratio of voltages or currents. Three decibels increase represents a doubling of power, six  
decibels increase represents four times the power or a doubling of the voltage in a circuit. 2. A  
derived unit of loudness. The human ear perceives a 10 decibel increase as twice as loud, and a 10  
decibel decrease as half as loud.  
Dedicated Line 1. A term used by some to indicate a single path in a point-to-point system. 2. A term used instead  
of point-to-point or matrix system, for example: a dedicated line system. (This term seems to be  
more marketing than engineering oriented).  
Destination A destination is anything that a talk key talks to or a listen key listens to. A destination can  
therefore be any port, Party-Line, IFB, etc.  
Dielectric An insulating (nonconducting) medium or material.  
Dim “Dim” occurs in two contexts in RTS™ Digital Matrix Intercom Systems.First, there is the Dim  
Table feature. Dim tables are used to correct a feedback problem that can occur between two  
keypanels operating in close proximity that have keys assigned to talk/listen to a common  
destination. Dim tables are set up in AZ™EDIT (search for keyword “dim” in AZ™EDIT help.  
Once a dim table is set up, it can be assigned as a level 2 talk assignment for those keys that are  
causing the feedback problem. For information about how to make this assignment from a  
programmable keypanel, search for “Dim Table” in the keypanel manual index.There is also an  
adjustable speaker dim feature available on the KP-32 Keypanel. This causes the speaker or  
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headphone volume to diminish by a preset amount whenever a talk key is activated. This can help  
to prevent occasional feedback between the speaker and microphone due to volume settings,  
microphone placement, etc. For setup and usage, search for “Speaker Dim” in the keypanel  
manual index.  
Distortion Distortion is the effect when the output of an electronic device contains undesired signals that  
were not present at the input. This is assuming that the electronic device is supposed to be a linear  
device. The undesired signals have a frequency or frequencies that are related to the input signal.  
If the frequency(ies) is/are harmonically related to a single frequency input, then the undesired  
signal is ‘harmonic” distortion. If the signal is the sum or difference of two input frequencies, then  
the distortion is called “intermodulation” distortion. If the distortion is the result of a pulse or step  
input, and the frequency(ies) is/are related to sums and differences of the frequencies determined  
by the Fourier transform of the input pulse or step input, the distortion is called “transient  
intermodulation distortion”. Distortion can occur both in active devices (e.g. amplifiers) or  
passive devices (e.g. transformers). Harmonic Distortion is measured in percentages or decibels  
below the fundamental signal. For example: a distortion of 0.1 percent is “60 dB down”.  
Intermodulation Distortion requires two input signals (say 1000 and 400 hertz) to be inserted and  
the sum and difference to be measured.  
Double Headset Headset with intercom in one ear and program in the other.  
Double-Muff Headset with two earphones plus a microphone. It can be connected monaurally (same  
Headset  
information, both ears) or binaurally (separate feed each ear). In binaural operation, the feed can  
be intercom in one ear and program in the other, or intercom channel A in one ear and intercom  
channel B in the other ear. Channels A and B are either conference line channels or other  
intercom feeds. To get a binaural feed requires a binaural/stereo capable user station such as  
BP320, BP325, Model 802, Model MCE325, or any station so optioned.  
Drain Wire An uninsulated wire in contact with a shield throughout its length, and used for connecting  
(“terminating”) the shield.  
Dry Pair / Dry A dry pair or dry line is a communications line that has audio signals but no direct current (DC)  
Line  
voltage or current.  
DSP Digital Signal Processor. Usually a microprocessor with two memory addressing capability. One  
memory is the program memory which tells the microprocessor what to do, and the second  
memory contains: data to be processed, intermediate results, and final results. The advantage of a  
DSP is its speed. It is fast enough to process analog (or audio) signals in real time, and is often  
used in that application. Some applications are system to system interfaces (e.g. Telos “Link” for  
interfacing a standard telephone line to an RTS™ Systems TW Intercom line).  
Dual Listen This is either an option or feature of intercom user stations. Dual listen permits an operator to  
listen to two channels at once. This may be a mix of two channels to one ear, or in a binaural or  
stereo user station, one channel can be assigned to one ear and the other channel to the other ear.  
Dual Listen could also be an intercom channel and a program audio source. The dual listen pots  
are functionally configured in one of three ways: 1. One pot controls the audio of the channel  
actively used, and the second pot controls the audio of a monitored channel. 2. One pot is always  
one channel and the other pot is always the other channel. 3. On three channel systems, operation  
is similar to 1. except if the active channel and the monitored channel coincide, the monitor feed  
is blanked out to prevent a 6 dB increase in volume and feedback.  
Dual Listen An option for user stations that allows a monaural mix of two channels. Usually the station has  
Option  
two volume controls, sometimes two concentric volume controls.  
Duplex / See Full Duplex, Half Duplex, or Simplex.  
Simplex  
Dynamic Converts sound pressure waves to electrical signals by means of a coil attached to a diaphragm  
Microphone  
moving in a magnetic field.  
E
E
A symbol for voltage used in electronics, and engineering. Also used as the symbol for the  
electric field (volts per meter).  
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Earth British term for a reference ground. Earth may mean power line ground or a facility zero-  
reference ground.  
Earphone A device used to hear an electrical audio signal. The earphone converts electrical signals to  
acoustic signals that can be heard.  
EFP Electronic Field Production. Production of television programming using field equipment (mobile  
trucks, portable gear, et cetera).  
EIA Electronic Industries Association (formerly RMS or RETMA).  
EIA Sensitivity Also called Gm rating. Adding the EIA sensitivity to the SPL at the microphone gives the  
microphone power output in dBm into a matched load. Sensitivities for open-circuit can be  
considered as follows: -65 dB re 1 volt / microbar = high sensitivity (usually results in better  
signal to noise ratio). -75 dB re 1 volt I microbar = medium sensitivity -85 dB re 1 volt / microbar  
= low sensitivity.  
Electret A microphone using a capacitor as the sound pressure sensing element. Electret microphones are  
Microphone  
a special case of condenser microphones in that they are permanently polarized and require no  
special polarizing voltage. Electret microphone outputs are high impedance and need to be  
buffered by an active device. The active device needs power so various battery, phantom, and A-  
B powering schemes are used to buffer the active device, (which is very close to or on the  
microphone diaphragm).  
Electronic Audio and other signals can be switched either electronically or mechanically. The electronic  
Switching  
versus  
Mechanical  
switching is generally faster and quieter, but usually has some losses. Mechanical switching is  
generally slower, noisier, but has less or little loss. In switching signals from current sources,  
electronic switching prevents loss of termination for a significant amount of time.  
Switching  
EMF Electromotive Force (voltage).  
Energy The capability of doing work.  
Energy Loss of energy by conversion to other forms, usually heat.  
Dissipation  
ENG Electronic News Gathering. Accomplished using television and accessory equipment in a small  
van, with the capability of relaying pictures and sound back to a broadcast station or network  
control center. The equipment used may be of special design, for example smaller “ENG type”  
television cameras.  
EMI Electromagnetic Interference. Interference caused by the radiation of electrical or magnetic fields  
from sources such as radio transmitters, light dimmers, computers, and transformers.  
Equalization The ability to correct or adjust non-uniform frequency response in a sound system. The  
(EQ)  
equalization may be applied to a signal to be recorded, that has been previously recorded or to a  
real time (“live”) signal.  
Equalizer An electronic device or circuit that allows for the adjustment of a signals frequency response.  
F
Farad A measure of the ability to store electrical charge between two conductors. Farad is named after  
Michael Faraday. A capacitance value of one farad can store one coulomb of charge at one volt.  
One farad permits one ampere of current when the voltage changes at the rate of one volt per  
second. Practical sizes are: millifarad one-thousandth of a farad, microfarad one-millionth of a  
farad, nanofarad one-thousandth millionth of a farad, picofarad one-millionth of a millionth of a  
farad.  
Feedback 1. Audio deliberately fed back to a user, for example a monitor for a musician to hear his own  
instrument or voice, 2. Audio feedback to a headset or earset as in IFB operations (see IFB), 3. An  
unintentional return of an electrical or acoustic signal to a microphone or amplifier input, the  
result of which is an oscillation.  
Filter A circuit that is sensitive to signal frequency and is capable of attenuating some signal  
frequencies and not attenuating others.  
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Film-Style Directing separate takes or scenes that are to be later edited in postproduction. These takes or  
Directing  
scenes are not necessarily in the same sequence as they will appear in the film or tape.  
FM Frequency Modulation. A method of adding audio to a radio frequency carrier. FM signals are  
usually more noise free than amplitude modulation (AM) signals. Wireless intercom units usually  
use FM.  
Follow Spot Used to accent or light action on stage, the follow spot is a focused high power light that focuses a  
beam from a large circle to a small spot. The operator of the follow spot is usually on the lighting  
intercom line, and sometimes in small productions on the primary intercom line. The follow spot  
operators have been known to tape their beltpack to the spotlight or a nearby metal structure. This  
practice can cause hum and noise in the intercom line because of the large currents involved in  
lighting. Some of the currents are induced into the metallic structure of the facility causing large  
“ground” currents. If a belt pack is to be taped to something, a layer of tape should be put around  
the belt pack first to insulate it from any metal. The newer BP325 has a nonmetallic case, so  
adding tape to the case is unnecessary, but it is necessary to prevent contact of connector shells  
and other metal objects with ground or metallic structures.  
Four-Wire A communications system where the path is different for talk and listen. In electrical pathways  
there are, in fact, four wires (two paths). Four-wire systems can be four- wire balanced and four-  
wire unbalanced.  
Four-Wire Four-wire balanced is similar to four-wire unbalanced except that conductors are not tied to  
Balanced  
circuit common. Circuit common is either tied to a transformer center tap, or is an electrical center  
point, or not tied at all.  
Four-Wire A four-wire system that uses a circuit common and two additional conductors. The talk pathway  
Unbalanced  
consists of one conductor plus circuit common. The listen pathway consists of another conductor  
and circuit common.  
Full Duplex Duplex communication allows simultaneous two-way conversations, that is one person can  
interrupt the other. In data communications, full duplex permits confirmation of sent data by the  
receiving terminal echoing or sending back the same data or confirming data.  
Frequency The number of times per second a periodic action occurs. Frequency is measured in Hertz  
(formerly cycles per second).  
Frequency The range of useful frequencies for a particular device, circuit, or system. For example: a  
Response  
microphone frequency response of 20 Hertz to 20,000 Hertz 3 dB would be considered  
excellent. The design goal of the TW system is 75 Hertz to 20,000 Hertz (system), 75 Hertz to  
10,000 Hertz (microphone preamplifier), and 75 Hertz to 8,000 Hertz (headphone/speaker  
amplifiers). The response on an actual system will vary according to the amount of cable in the  
system, various trade-offs, and the number of stations in the system.  
G
Gain 1. Level of amplification for audio/video signals. Operators may need to periodically adjust these  
levels during production (especially those gain controls on the audio mixer board). 2. An  
important parameter of a functional block or a circuit device. The gain is the output voltage  
divided by the input voltage, the output current divided by the input current, or the output power  
divided by the input power. For example: a microphone preamplifier in a TW user station may  
have a maximum gain of 54 dB (a voltage ratio of 500). Note that, in the case of the bilateral  
current source, it is a voltage controlled current source, and is characterized not by gain, but by  
transconductance. Transconductance is given by the output amperes divided by the input volts.  
The units of transconductance are siemens (formerly the units were mhos). The bilateral current  
source used in RTS™ Systems user stations usually has a transconductance of 5 milliamperes  
divided by 1.5 volts or 3.3 millisiemens.  
GND An abbreviation for ground.  
GPIO General Purpose Input / Output. (You may also see this referred to simply as “GPI”.) GPIO is a  
means of controlling devices using switch contact closures, DC voltages, or similar methods. For  
example: you can control a lighting system from keypanel keys, or key a transmitter from a talk  
key during transmit. Or, simply operate a light or buzzer for cueing. In ADAM™, ADAM™ CS,  
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and Zeus™ intercom systems, you can also control intercom events from external switches. For  
example: you can activate key assignments, close or open crosspoints, activate GPI outputs, etc.  
In CS9000 Series intercom systems, general purpose control outputs are provided by optional  
FR9528 Relay Frames (8 relays each). In those systems, a relay may be assigned to an intercom  
key on a keypanel using the Relay key assignment type. Pressing the intercom key activates the  
relay. ADAM™, ADAM™ CS, and Zeus™ intercom systems all have a dedicated GPIO  
connector (J27 on a Zeus™ Frame, J903 on an ADAM™ CS Frame, and J11 on the XCP-  
ADAM™-MC Master Controller Breakout Panel in an ADAM™ Intercom System). This  
connector supports 8 control inputs and 8 control outputs. Additionally, one or more UIO-256  
Universal Input/Output frames may be connected to the intercom system. Each UIO-256 provides  
another 16 control inputs and 16 control outputs. Control outputs may be assigned to intercom  
keys using the Relay key assignment type, and the intercom keys can then control external  
devices the same as the FR9528. Control inputs can be assigned to activate “virtual” key  
assignments. (A virtual key assignment is a key assignment at an intercom port where there is not  
actually any keypanel connected. Basically, you use an external switch to act like a talk or listen  
key.) The control inputs and outputs can also be used as conditions for UPL statements in  
AZ™EDIT.Finally, there is a GPIO option available for the KP-12 keypanel, and a connector  
module option for the KP-32, which includes GPIO. These are referred to as “Local” GPIO, since  
they are assigned and used locally at the keypanel. Each local GPIO includes 4 control inputs and  
4 control outputs.  
Green Room A room for performers / talent to stay just before making their appearance on stage. This room is  
usually close to the stage, and has amenities plus a video and audio monitor.  
Ground The term ground has several meanings. One meaning is a circuit common point potential. Another  
meaning is a 0 volts point. Another meaning is a connection to the earth. Another meaning is the  
chassis of radio equipment. Radio Frequency engineers almost always connect circuit return to  
the chassis. This can cause a ground loop in systems if the chassis is connected to earth ground as  
well, and the circuit return in the system encounters another earth ground. The TW system circuit  
return is bypassed to earth ground and tied to earth ground through a 10,000 or 22,000 ohm  
resistor, in order to prevent ground noises or hums from being introduced into the intercom  
system. Connection of a chassis grounded device to the TW System should be done through an  
audio isolation transformer.  
Ground Loop A ground loop occurs when a system circuit common is tied to earth ground or another ground or  
another conductor at two places in the system. This allows “ground currents” to be superimposed  
on the intercom system circuit common, causing hum and spurious noises.  
Ground Often the potential of the earth, but also the potential at a zero voltage point in a system or an  
Potential  
electrical/electronic circuit.  
H
Half Duplex Half Duplex communication allows two-way conversations, one-way at a time, such that one  
person cannot interrupt the other. In data communications, half duplex means sent data is not  
confirmable by the receiving end on a continuous basis.  
Harmonic A distortion at the output of a device where the amplified input signal is accompanied by the sum  
Distortion  
of unwanted signals that are harmonics o the input signal. Harmonic distortion can be expressed  
as a percentage of the total output intensity, or in decibels. See also Distortion.  
Headphones / Headsets are headphones with microphones added. Headphones and headsets are available in a  
Headsets  
wide range of variations. Some of the variations include: Lightweight, Heavyweight, Medium  
Weight: Lightweight can often be used or worn for a ten hour shift with only mild discomfort;  
medium weight usage ranges from two to six hours continuous, and heavy weight usage ranges  
from 15 minutes to 2 hours. Acoustic Isolation: which varies from 0 dB to 40 dB. Usually more  
isolation means a heavier headset. Acoustic Isolation (30 to 40 dB) is required in high ambient  
noise environments such as concerts, auto racing, construction areas, aircraft engine run-up, near  
machinery such as printing presses. Medium isolation (10 to 20 dB) is required in quieter  
concerts, near crowds, near quieter machinery. Low acoustic isolation can be tolerated in  
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environments such as television studios (news). Impedances: Impedances of headphones range  
typically from 2000 ohms to 2 ohms. Common impedances per earphone are 300 ohms, 150  
ohms, 50 ohms, 25 ohms. Headphone total impedances depend on the earphone impedance and  
whether they are connected in series or parallel. The headphones in standard headsets sold by  
RTS™ Systems ranges from 25 ohms to 300 ohms. Military headphones may be very low  
impedance, 10 ohms or less. A fuel tank entry system sold by RTS™ Systems has 2000 ohm  
headphones. Lower impedance headphones allow a louder sound (up to 110 dB SPL) to be  
generated with relatively low voltage in the user station (say 12 volts DC). Microphone Types:  
(for headsets) The microphones types may be carbon, carbon emulate, dynamic, electret. The  
carbon types produce high output levels but have higher distortion, the carbon emulate types, put  
out high levels with low to moderate distortion but require special electronics and a way to power  
the electronics. The electrets usually have electronics built on the microphone, but there is no  
voltage gain from this electronics, just impedance matching (from megohms to kilohms).  
Electrets have about 10 dB more level than dynamics, but are very prone to “popping”. To  
prevent popping, windscreens need to be installed or placed over the microphone element, and the  
following circuit should have a circa 500 hertz high pass roll off. Dynamic and electret  
microphones usually have low distortion and good frequency response (100 to 8,000 hertz). Some  
dynamic microphones made with low technology may have poor frequency response. Some  
typical microphones impedances are as follows: carbon: small button 600 ohms, large button, 50  
ohms; dynamic: 2 ohm (military), 150-200 ohm (RTS™ Systems recommends), 600-1000 (lower  
cost push-to-talk and others). Microphone impedances can also be higher such as 50 kilohms, but  
these usually are not on headsets. Most RTS™ Systems User Stations microphone inputs allow  
for an impedance range of 50 to 1000 ohms for dynamic microphones, 1000 to 2000 ohms for  
electrets, 50 to 200 ohms for carbon or carbon emulate.  
Headroom The difference between the instantaneous level of a signal and the peak signal possible in a given  
system. Headroom is often expressed in decibels. System headroom in the TW system is about  
eight to ten dB. Headroom for the microphone input is an apparent 40 dB because of the 30 dB  
limiter compression ratio. Because of the design of the TW and 800 series systems, and the  
consistency of levels, the peak to average speech ratio is close to 10 dB.  
Hertz The unit of frequency, cycles per second. One thousand hertz equals one kilohertz equals one  
thousand cycles per second.  
Home Run Running the user station system connection cables to a central point (as opposed to Daisy  
Chaining).  
Hot 1. A wire actively carrying power or signals. 2. Equipment that is turned on, for example a “hot”  
microphone.  
Hum Hum is an interfering addition to audio. Its frequency is within that of human hearing and it is at  
the frequency of the power line or its harmonics. For example: a pickup of the fundamental will  
result in a 50, 60, or 400 hertz tone in the audio. If the hum is due to excess ripple in a full wave  
rectified supply the frequency will be 100, 120, 800 hertz. If the power line waveform is distorted  
(which it often is), other harmonics will be heard. Hum is induced electrostatically via unshielded  
wires in high impedance circuits, or electromagnetically via unshielded dynamic microphones,  
transformers, tape recorder heads, or ground loops.  
Hypercardioid A microphone pick-up pattern. This pattern has its maximum rejection at 100° off axis. This  
pattern has good rejection of far field sound and room reverberation. Good in house speaker  
systems.  
I
I
Symbol used to designate current.  
IBEW International Brotherhood of Electrical Workers  
IFB The IFB * System is a special intercom system used for television shows with highly flexible  
formats or where important program changes are likely, for example, newscasts or special events  
telecasts. The IFB system connects control room personnel such as the director, producer, audio  
mixer, and technical director directly with the performers or “talent”. The performer wears a  
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either a small earpiece or headset ** that carries the program sound unless the director or another  
member of the production team operates the IFB and interrupts the program sound with special  
instructions. * IFB means Interrupted Feedback, or Interrupted Fold-Back. This system is also  
called Interrupted Return Feed (IRF), program Interrupt, or prompt-mute. ** In sports, stadium,  
and parade remotes, a double muff headset is used. Impedance is the resistance to an alternating  
current.  
Impedance Impedance is composed of resistance and reactance (rectangular coordinate representation).  
Impedance can also be viewed as a vector quantity with a magnitude and a phase angle.  
Impedance can be measured with an impedance meter. Impedance may vary with frequency. In  
the discussions in other sections, the impedance is usually that at one kilohertz, unless otherwise  
specified. The unit of impedance is the ohm. An impedance stated in rectangular coordinates is a  
complex number. In RTS™ Systems equipment the impedance is important over a band of  
frequencies and this band is normally stated in the specifications.  
Inductance A property of a conductor or circuit that resists a change in current. Transformers, coils, chokes,  
wires, and printed circuits have inductance. Inductance is measured in henries. The symbol for  
inductance is L.  
Insertion Loss A measure of the attenuation of a device by determining the output of a system before and after  
the device is inserted into the system.  
Intercom 1. A means of organizational communications. The design of the intercoms systems produced by  
RTS™ Systems focuses on the concept of team communications. A team is an organization of  
members who perform individual tasks to accomplish a team goal or objective. The intercom is  
the pathway or means for the voice communications used to coordinate the team activity. 2. In  
larger systems, intercom refers to the matrix or point-to- point communications equipment, and  
interphone refers to the conference type equipment.  
Intercom Data For data routing purposes, port numbers are arranged in groups of 8 sequential intercom ports. In  
Groups and Port  
an ADAM™ or ADAM™ CS Intercom System, each Audio I/O card comprises one data group.  
In a Zeus™ Intercom System, each group of 8 port connectors comprises a data group. Within  
each data group, each keypanel is uniquely identified by its address setting. Whenever you  
Number  
Calculation  
display the Panel ID, the intercom system determines which data group the keypanel is connected  
to, and also the address setting. It then reports the calculated address. For example: suppose a  
keypanel is connected to data group 3 and the keypanel address is set to 5. Since each data group  
consists of 8 sequential intercom ports, the calculated port number for this keypanel will be (2*8)  
+ 5, or 21. This is the total of all intercom port numbers on the first 2 data groups, plus the offset  
of 5 ports into the third data group.  
Interconnect A cable, device, or method of connecting one device to another, or one system to another.  
Interface The place where two systems or a system and a subsystem meet. Also the device that adjusts  
levels and other parameters such that one system appears to the other system as a compatible  
extension.  
Intermodulation See Distortion.  
Distortion  
Inverse Square The decrease in level as a listener moves away from a loudspeaker, or a microphone is moved  
Law  
away from an acoustic source. The law says that the sound pressure will decrease six dB every  
time the distance is doubled. This law applies to the outdoors, and to the indoors where  
reverberation and room effects are negligible.  
IR Drop Applies to the voltage drop along a wire as a function of the current (I) and the resistance of the  
wire (R). For example, the resistance of 10,000 feet of a number 22 gage pair is 320 ohms. The  
DC voltage drop at the end of the wire due to a user station using 50 milliamperes of current is  
0.040 amperes times 320 ohms equals 12.8 volts. If the power supply is 32 volts and the drop is  
12.8 volts, the voltage at the end of the wire is 19.2 volts. The minimum operating voltage for a  
user station operating in the high impedance mode is 18 volts. So a belt pack user station such as  
the BP317, or BP300 has enough DC voltage to work at the end of 10,000 feet of a 22 AWG wire  
pair.  
Isolation The ability of a circuit or component to reject interference, usually expressed in dB.  
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ISO (Camera ISO is a means for a keypanel operator to isolate a particular intercom port for private  
ISO)  
communication. While the intercom port is isolated, it can only hear audio from the keypanel  
operator. ISO is frequently used in television broadcasting to temporarily isolate a member of a  
camera Party-Line. The isolated camera operator can then receive directions without interference  
from other audio traffic on the Party-Line. ISOs are setup using the intercom system  
configuration software. Each ISO can also be given a name which is meaningful to keypanel  
operators. Once an ISO has been set up and named, it can be assigned to any keypanel key  
(provided that ISO assignment has not been restricted or disabled in the intercom system  
configuration software). For further information about ISOs, search for “ISO” in AZ™EDIT help.  
J
K
k
(kilo) metric prefix symbol for 1000.  
K
(Kilobyte) prefix symbol for 1024 (common usage).  
kilo A prefix meaning 1000.  
L
L
Symbol for inductance.  
Lavaliere A small microphone. There are two types: 1) a very miniature type that clips onto clothing on the  
front of a performer below his head, and 2) a larger microphone on a cord worn around the neck  
of the performer with the microphone hanging below the neck on the chest.  
Leakage The undesired leakage of a current or signal into another path.  
Level The amplitude of power of a signal. If in decibels, the level has to be stated relative to a reference,  
and the reference has to be made clear.  
Light Signaling See Signaling. Accomplished on the intercom line, using DC levels (Clear-Com®, HME, Theatre  
Visions) or a 20 kilohertz tone (RTS™ Systems, Telex® AudioCom®).  
Limiter An effective communications system needs to limit dynamic range to ensure adequate  
intelligibility to the listener. The limiter/compressor in the TW system user stations has three  
functions: I) It helps loud talkers and soft talkers to be heard equally well, 2) It prevents a loud  
voice from being severely distorted, 3) It keeps the voltage levels from exceeding system limits.  
Function 3 is important because the user station must operate over a wide range of power  
voltages, and the limiter makes a practical system possible.  
Line A single communication path.  
Line Level Line Level depends on the system and the reference. It is often used to differentiate microphone  
level (-40 to -60 dBu) and a higher level (often 0 dBu).  
Local Power Local Power Source is a small AC converter that converts AC line power to low voltage in order  
Option  
to power a user station --a separate connector is provided. User stations usually get DC from the  
converter, although occasionally low voltage AC power is used.  
Loop-Through See “Daisy Chain”.  
Loudspeaker A transducer that converts the electrical output of an amplifier to a audible sound.  
M
mA Shorthand for milliamperes or thousandths of an ampere.  
Main Station A user station where a user station and a system power supply are combined into one package.  
Master Station A multichannel user station. There may be one or more of these stations in a system. Another  
definition is the primary station in a system.  
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Matrix “Matrix” is a term inherited from earlier point-to-point intercom systems, where all point-to-point  
communication was accomplished by closing specific switches in a switching matrix. Examples  
include the RTS™ CS9500, CS9600, and CS9700 Intercom Systems. In many instances,  
“Matrix” is used interchangeably with “Intercom System”. RTS™ ADAM™, ADAM™ CS, and  
Zeus™ Intercom Systems, on the other hand, do not use a switching matrix, but use a method  
called Time Division Multiplexing (TDM), in which communications are routed as digital  
packets. However, use of the term “matrix” persists since packet routing basically accomplishes  
the same thing as a conventional switching matrix: namely, connecting distinct talkers and  
listeners.  
Maximum SPL The acoustic level above which operation changes from linear to nonlinear. This is a specification  
usually for microphones.  
Mho The old unit of conductance or transconductance, now a siemen. The more familiar units of  
transconductance are amperes (output) per volts (input). For electronic devices, the units are  
usually millisiemens or milliamperes per volt.  
Mic Short for Microphone  
Micro (µ) Micro is a prefix meaning one millionth. For example a one microfarad capacitor has a  
capacitance of a millionth of a farad.  
Microcontroller A Microprocessor that has a built in RAM (Random Access Memory), built in ROM (Read Only  
Memory), parallel type inputs / outputs, and often a serial input / output.  
Microphone A transducer that converts sound into an electrical output or voltage.  
Microprocessor The heart of a computer on a chip. Has inputs and outputs and can read RAM (Random Access  
Memory) and ROM (Read Only Memory). Used in the Model 802 to process stimuli such as  
button pushing and incoming tally signals and produce reactions such as blinking or steady lamp  
illumination, crosspoint closure, tally generation, relay control, or audible chime signal.  
milli (m) A prefix that means one-thousandth.  
Mixer An electronic device used to combine several signals inputs to a single output or to stereo outputs.  
Often other features are added to make it easy to achieve the basic goal.  
Mix-Minus Bus / 1. In the studio, a mix-minus feed can be fed to a singer on stage. The mix- minus consists of a  
feed  
prerecorded orchestra. The performers microphone signal and the mix-minus feed are combined  
in another mixer output for the final air or recorded feed. This method is used for reasons of  
economy and to simplify production. 2. In ENG operations, a mix-minus feed is used for the IFB.  
The mix-minus allows the talent to hear the program audio that includes the voices of other talents  
at other venues, but not the talent’s own voice. The effect is to allow more normal conversations,  
on air, among the performers. The bus feed refers to the mixer mix-minus feed available to one or  
more IFB program inputs.  
Monaural Containing one source of audio although the source may be a summation of two or more original  
sources.  
Monitor An audio speaker used to supply program audio to the control room, audio mixer, and to others  
who need an acoustic audio feed. Some special monitors are used for musicians to hear their own  
instrument or voice. Usually a monitor is placed in the Green Room.  
Mu (µ) Greek letter, mu, symbol for permeability (magnetic), amplification factor, prefix for micro (one-  
millionth).  
Mu Metal Shield A highly effective magnetic shielding material.  
Multiplexing A method of carrying more than one signal on a single “path.” Multiplexing may be by means of  
frequency, time division, and / or space. The TW system frequency multiplexes DC power,  
speech signals, and a 20 kilohertz call signal on a single pair of wires. The Models 848A / DC848  
use time multiplexing in a digital RS485 signal to send data for all 24 stations down a single path.  
mV Millivolt or one thousandth of a volt.  
mW Milliwatt or one thousandth of a watt.  
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N
O
NAB National Association of Broadcasters.  
NABET National Association of Broadcast Employees and Technicians.  
NEC National Electrical Code  
NEMA National Electrical Manufacturers Association  
Nibble A nibble is half a byte or four bits.  
Noise Usually an unwanted sound or signal that interferes with a sound or signal normally present in a  
system, device, or circuit. Sometimes a special noise source such as a pink noise source or a white  
noise source is used to test a system or acoustically test a room.  
Ohm The electrical unit of resistance. One volt will maintain one ampere of current through one ohm.  
Ohm’s Law This law relates the electrical parameters of voltage, current, and resistance. The symbol for  
voltage is V*, current is I, and resistance is R. Voltage, V=I*R. Current, I=V/R. Resistance,  
R=V/I. *An older symbol or term for voltage is E. E is also the symbol for the Electric field,  
which has units of volts per meter.  
Omega () Symbol for ohm.  
Omnidirectional A microphone that picks up sound from all directions with the same amplitude.  
Microphone  
Option Options are extra features available (for a price) on intercom and pro-audio equipment.  
Output The useful signal (voltage, current, power) produced by a system, device, or circuit.  
P
Paging Making a voice announcement over a sound system. The sound system is “P.A.” in the sound  
contractor world, and “SA”, Stage Announce, in the television / theater world.  
Parallel Circuit In a circuit, the paralleled elements would be across the same voltage and the currents would  
or Connection  
divide amongst the elements. This kind of connection can apply to circuits, devices, or systems.  
For example: two RTS™ Systems TW Intercom Systems can be paralleled, by coupling with the  
appropriate capacitors, and switching each system power supply(ies) from 200 ohms to 400 ohms  
on the channels to be paralleled.  
Party-Line (PL) A Party-Line (also called a conference line) is a group of intercom ports which can always talk  
and/or listen to each other. Party-Lines have default names PL01, PL02 etc. These names can be  
changed to more meaningful names using Other Alpha setup in AZ™EDIT. Members are  
assigned to a Party-Line using Party-Line setup in AZ™EDIT. Once a Party-Line has been set up,  
it can also be assigned to a keypanel key either from the configuration software or at a  
programmable keypanel. This allows the keypanel operator to talk and/or listen to the Party-Line  
without being a member. IMPORTANT: Do not confuse special lists and Party-Lines. A special  
list is used when a keypanel operator needs to occasionally talk or listen to a group of intercom  
ports that are otherwise unrelated. A Party-Line is typically used when several users of non-  
keypanel devices (such as belt packs or camera intercoms) are engaged in a specific common  
activity and they need to talk and/or listen to each other all the time. Keypanels are almost never  
members of Party-Lines (although they can be). However, a keypanel key can be assigned to  
occasionally talk or listen to a Party-Line if desired. Just remember: Party-Lines are primarily set  
up for Party-Line members, with occasional access by keypanel operators, while special lists are  
set up exclusively for keypanel operators to talk or listen to several unrelated intercom  
poRTS™.For specific information about Party-Line setup, search for “PL” or “Party-Line” in  
AZ™EDIT help.  
Patch Bay / A system of interconnecting audio signals. Consists of fixed connectors interconnected with  
Patchboard  
flexible “patch” cords that are cords usually with a male connector on each end.  
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Peak The crest value of a voltage, current, or power.  
Phantom Power There are three standard voltages: 12, 24, and 48, according to DIN 45 596. Voltage is applied to  
the circuit in a balanced fashion using a center tapped transformer or two resistors. The size of the  
resistors depend on the voltage.  
Phase, Phase Comparing the reference of one waveform to the reference point of another waveform. With  
Shift  
periodic waveforms, the phase varies from 0 degrees (waveforms line up), to 180 degrees  
(waveforms opposite), to 360 degrees (waveforms line up but one is delayed by the time of one  
waveform).  
Pi (π) Symbol for the quantity 3.14159...  
Pickup Pattern Refers to the sensitivity of a microphone to acoustic audio signals originating from different  
spatial directions.  
Pink Noise Equal noise energy per octave.  
PL See Conference Intercom Systems.  
PLL Phase Lock Loop. A tone decoder utilizing a phase lock loop is used in many of the TW System  
stations.  
Point-to-Point A point-to-point system allows two or more people to intercommunicate. But the conversations  
(Matrix)  
Systems  
are limited to those selected by the originator of the call. This system normally includes a “tally”  
subsystem. The “tally” subsystem tells the called station where the originator is so that the called  
station operator can press a button to answer. Some systems automatically press the button and  
complete the return path. Most systems made by RTS™ Systems are full duplex (one can  
interrupt the speaker), and non- blocking (access to the channel is immediate and there is no busy  
signal). Conversations on point-to-point systems are in general, private. There are two kinds of  
point-to-point systems available. One is a distributed matrix system; the other is a central matrix  
system. The Models 848A and DC848 are modules in a distributed matrix system. The McCurdy  
Models 9500 and 9400 are examples of central matrix system.  
Pop An undesired effect on a microphone output when a puff of air hits the microphone diaphragm.  
The effect sounds like a thump or pop. The effect is noticed with the following sounds: “p”, “b”,  
“t”.  
Pop Filter Material placed between a sound source and a microphone that reduces the “pop” effects. It  
slightly affects microphone performance.  
Port Ports are the individual channels that devices are connected to. Devices include: 2-way  
communication devices, such as keypanels, belt packs etc. Audio sources, such as broadcast feeds  
or background music. Miscellaneous audio output devices, such as powered loudspeakers, PA  
systems etc.  
Port Gains RTS™ Keypanels are calibrated to send and receive audio at the standard operating levels of the  
intercom system. No audio gain adjustment is normally required when connecting these.  
However, many other types of devices may not operate at the standard intercom system levels. To  
assure signal level compatibility between the various types of audio devices connected to the  
intercom system, there are separate analog input and output gain adjustments for each intercom  
port. It is also possible to adjust the listen gain for any specific intercom port when listening to  
any other specific intercom port. This is called the point-to-point listen gain, or crosspoint gain.  
For example, a keypanel operator might want to monitor a music source connected at some  
intercom port, but at a reduced audio level so that it does not interfere with normal intercom  
communications. The crosspoint gain can be reduced for the keypanel port listening to the port  
where the music source is connected.Analog gain adjustment is only available using AZ™EDIT.  
Crosspoint gains can be adjusted either within AZ™EDIT or from a programmable keypanel. For  
further information on any gain adjustment in AZ™EDIT, search for keyword “gain” in  
AZ™EDIT help. For procedures to adjust gain from a programmable keypanel, look for “gain” in  
the manual index.  
Port ID Numbers Intercom ports have identification numbers 001, 002 etc. These numbers cannot be changed, but  
and Alphas  
may not be commonly known to intercom system users. Each intercom port also has a default  
name, called an “alpha”, because this name appears in the alphanumeric displays on keypanels  
when you assign the ports to keys for talking and listening. The default alpha names are N001,  
N002 etc. These default alpha names can be changed to ones that are meaningful to keypanel  
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operators using Port Alpha setup In AZ™EDIT. (Click the “Port Alpha” button in AZ™EDIT,  
then press F1 on the computer keyboard if you need help.)  
Postproduction Production activity that occurs after the actual production phase. For example the editing of a  
television or motion picture production.  
Postproduction The process of making decisions and actually manipulating the media (film or tape) to change  
Editing  
action sequences, delete, insert, and modify images and sound.  
Pot A device to electrically change audio or video levels. Potting up means increasing a level from a  
(Potentiometer)  
control panel. An audio mixing console is an audio control panel.  
Power Amplifier An amplifier used for driving lower impedance (8 to 500 ohms) headphones or speakers (2 to 45  
ohms).  
Power Supply 1) The source of electrical power (“power outlet”). In North America this source is generally 120  
volts AC, 60 hertz. In Japan the source is generally 100 volts, 50 or 60 hertz. In Britain the source  
is 240 volts, 50 hertz. In Europe the power is usually 220 volts, 50 hertz. There are exceptions in  
every location, and there are still isolated odd systems throughout the world. RTS™ Systems  
equipment has been designed to operate at these various voltages. In addition, some equipment is  
operable off of DC sources such as batteries, automobile 12 volt power, aircraft 28 volts, and  
aircraft 120 volts, 400 hertz. 2) A unit used for converting power outlet power to DC power.  
Power Supply, A special power supply to run user stations on the RTS™ Systems TW system. This supply  
TW  
provides low noise DC power (nominally 32 VDC) and an audio impedance of 200 or 400 ohms.  
This impedance extends from 100 hertz to 20000 hertz.  
Power Ratio See decibel.  
Preamplifier An amplifier usually used to raise the small signal from a microphone to a “line level” sized  
signal.  
Presence Peak A rise in the response of a microphone in the range of 2000 to 10, 000 hertz. In circuits, a  
deliberate alteration of the frequency response in the range of 1000 to 10,000 hertz. RTS™  
Systems Model 802 has a small presence boost in the speaker amplifier change in the 1000 to  
2000 hertz range.  
Pressure Zone Used to pick up audiences or groups. A microphone with a reflecting surface such that the sound  
Microphone  
waves arrive in phase at the microphone element, providing good frequency response. Also used  
for orchestral pickup.  
(PZM)  
Program, In television, the audio signal that is being sent out with the picture to be broadcast.  
Program Audio  
Push- To- Talk Usually used on handsets or push-to-talk microphones. Pushing the button enables the  
(PTT)  
microphone and often also enables an electronic switch in an intercom station. The electronic  
switch prevents amplifier and cable pickup from going on the intercom line as undesired noise.  
Q
R
R
Abbreviation for resistance, and the symbol for a resistor.  
Rack Unit(s) A standard unit of measure used when dealing with electronic equipment racks. 1 RU = 1.75”  
(RU)  
(44.45 mm). For example: a particular piece of equipment is described as being 3 RU in height.  
This means that it is 5.25” (3 x 1.75”) in height. Detailed information on the specification of  
standard electronic equipment racks can be found in EIA RS-310-D (See the references section).  
Reactance A property of an inductor or capacitor that is frequency dependent. Capacitive Reactance is  
opposite to Inductive Reactance. Inductive reactance increases with frequency. Capacitive  
reactance decreases with frequency. See Capacitance and Inductance.  
Relay Relay is used interchangeable with GPI output. The relay feature works with the 16 GPI outputs  
of an optional UIO-256 Universal Input / Output Frame, and with the relay outputs of an FR9528  
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Relay Frame. The relay feature also works with the 8 GPI outputs of an ADAM™, ADAM™ CS,  
or Zeus™ intercom system (J27 on a Zeus™ Frame, J903 on an ADAM™ CS Frame, and J11 on  
the XCP-ADAM™-MC Master Controller Breakout Panel in an ADAM™ Intercom System).  
You can assign a keypanel key to control a GPI output from any of these devices, and then use  
that key and output to control an external device. For example: you could use a keypanel key to  
control lighting. Or, you could assign a relay as a level 2 talk key assignment in a stacked talk key  
arrangement to both send audio and key a device, such as a paging amplifier or a 2-way radio.  
Remote Station A user station located at a distance from the master station.  
Remote Truck, A mobile television studio. Supports television productions with equipment and production  
Remote Unit  
personnel operating positions. Carries cameras, CCUs, switcher, monitors, audio console and  
ancillary equipment, VTRs, and last, but not least, intercom systems.  
Resistance In DC circuits, the opposition to current, in AC circuits, the real part of the opposition to current.  
Resonance A condition where an applied signal’s frequency coincides with a natural response frequency of a  
circuit, device, or system. There must be reactances in the circuit for a resonance, a pure  
resistance doesn’t resonate.  
Retractile A cord whose jacket is treated and formed to retract as a spring.  
RF Radio Frequency. Frequencies generally ranging from 15 kilohertz to 150 gigahertz. The  
electrical energy at these frequencies is often converted to electromagnetic waves that are  
propagated through space. These waves are the basis of the wireless intercom, radio broadcasting,  
television broadcasting, microwave ovens, industrial processes. Frequency Name of Band  
Examples: 3 to 30 kilohertz Very Low Frequencies (VLF) Underwater Communications 30 to  
300 kilohertz Low Frequency (LF) Navigation 300 to 300 kilohertz Medium Frequency (MF) AM  
Radio Broadcasting 3 to 30 megahertz High Frequency (HP) Short Wave Radio, Long Range  
Terrestrial Communications 30 to 300 megahertz Very High Frequency (VHF) TV, PM  
Broadcast, Fixed I Mobile Communications, Walkie Talkie, Wireless IFB, Wireless Intercom,  
Airborne Communications 300 to 300 megahertz Ultra High Frequency (UHF) TV Broadcast,  
Mobile Communications, Walkie Talkie, 3 to 30 gigahertz Super High Frequency (SHF) Satellite  
Uplink/Downlink 30 to 300 gigahertz Extremely High Frequency (EHF) Satellite Uplink/  
Downlink kilohertz = 1000 hertz megahertz = 1000000 hertz gigahertz = 1000000000 hertz  
RFI Radio Frequency Interference. This interference may originate from AM and FM radio stations,  
television stations, light dimmers, electric motors, intermittent incandescent or fluorescent lamps,  
doorbells, et cetera. It results in either direct demodulation into audio circuits or position sensitive  
effects.  
RMS The abbreviation for root-mean-square. The effective value of an alternating current waveform.  
The root-mean-square current, power, or voltage is as follows: Square the amplitude, so that the  
positive and negative halves of a waveform are the same polarity. Then the value is averaged over  
time. Finally the square root of the average or mean is taken. The RMS value of a one volt peak  
sine wave is 0.707  
Roll-off The frequency at which the response of a filter, circuit, network, device, or system changes from  
its center value by 3 dB.  
RU See Rack Unit(s).  
S
SA or S.A. Stage Announce. A public address system originating in a control room and ending up on the  
stage. The SA may also have the functionality of an IFB. This allows the director to interrupt  
dance music and address the dancers. The SA function is a standard function on the Series 4000  
IFB system, the Model 801 / Model 860 system, and the Model 802/ Model 862 system. The SA  
function is available as a special option on almost any RTS™ Systems user station. In the option  
case, the SA does not necessarily include the IFB function. An IFB option has to ordered to assure  
IFB functionality.  
Semiconductor A material whose conductivity falls between a conductor and an insulator. Semiconductors  
include the elements carbon, silicon, and germanium in crystal form. Other semiconductors  
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include compounds. Some examples are semiconductor diodes, transistors, integrated circuits,  
transector overvoltage devices, thyristors, and carbonized substances.  
Sensitivity 1. The electrical output of a microphone for a given SPL input. Open circuit sensitivity is the  
output voltage a microphone produces (in dB relative to 1 volt) into an open-circuit load, at a  
sound pressure of 74 dB SPL (1 microbar or 0.1 pascal). In practice, this is hard to do because of  
ambient noise, so readings are taken at 94 dB and the calculation adjusted accordingly. 2. Defined  
as the on-axis sound pressure level at a distance 1 meter in front of a speaker driven by 1 watt  
continuous average input power of a specified waveform. 3. Defined for headsets to indicate the  
SPL generated for a given set of conditions. The Beyer DT 108 headphone has a sensitivity of 94  
dB SPL produced for one milliwatt input. The Telex® PH10 headphone has a sensitivity of 105  
dB SPL produced for one milliwatt input. A Telex® EMV -2 announcer earset has a sensitivity of  
120 dB.  
Series Circuit An arrangement of circuit elements, circuits, devices or systems such that the components are  
arranged and connected end to end to form a single current path.  
Shield An electrostatic shield prevents crosstalk from one conductor to another by blocking the electric  
field. For example: by shielding wires in a cable, crosstalk can be dramatically reduced. A  
magnetic shield prevents electromagnetic coupling of undesired signals from one transformer to  
another. For example: the magnetic field from a power transformer to an audio output transformer  
can be attenuated by mu metal shielding.  
Shotgun A highly directional microphone for long distance pickup. Looks like a shotgun.  
Microphone  
Sidetone In the truest sense, sidetone is a small amount of microphone signal that is fed back to the  
earphone of the individual speaking into the microphone. In RTS™ TW user stations, the null  
balance control is sometimes used to adjust the amount of sidetone the user hears. This control is  
sometimes (technically erroneously) called the sidetone control. Other RTS™ TW equipment  
have both null balance adjustments and a true sidetone adjustment (Models 802, 848 for  
example).  
Signal The name applied to visual, audible, or electrical energy that carries information.  
Signal to Noise In a given circuit, device, or system, the ratio of the Signal plus Noise to Noise. The noise spoken  
Ratio (S/N or  
of is the residual noise in the system when no signal is present. The signal is a signal at a reference  
level representing typical operating conditions of the system. This ratio is usually specified across  
[S+N]/N)  
a frequency band. The S/N ratio of a microphone is specified at a given SPL ratio. For example, a  
S/N ratio of 60 dB at 94 dB SPL is considered good, 65 dB, very good, 70 dB is excellent.  
Sigma Symbol for summation, also used to indicate a summing amplifier or summing function.  
Signaling Signaling in these intercoms has several meanings. In the TW system, signaling is accomplished  
by a blinking light initiated from any Call Light equipped station on that channel. Signaling is  
often used to get attention such as getting someone to put their headset back on, or getting a sound  
mixer person to turn down the monitor speaker and talk on the intercom. Signaling can also be  
used as a visual cue. The blinking light can be used for a cue, but theatre productions often prefer  
a steady light. The light coming on is a “Standby” signal. The light going from on to off is an  
“Execute” signal.  
Simplex Simplex communication is one person at a time. There is only one communication channel  
available and it is unidirectional at a time, usually in the direction determined by the call initiator.  
An example of this is a CB or Citizens Band radio.  
Single-ended Unbalanced, using circuit common or “ground” as a return lead.  
Single Channel / In the RTS™ Systems TW Intercom system, most user stations are two channel. Other channel  
Two Channel  
numbers available (some optional some standard) are 1, 3, 4, 5, 6, 10, 12, 24. The term channels  
usually is applied to conference style user stations. The TW system can carry two channels on a  
standard microphone cable. Other systems carry one balanced channel (Telex® AudioCom®), or  
one unbalanced channel (Clear-Com®, Telex® AudioCom® in unbalanced mode, HME, Theatre  
Vision).  
SMPTE Society of Motion Picture and Television Engineers. An organization that (among other things)  
pioneers standards used in the television industry.  
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SMPTE/EBU Recorded on videotape or audiotape. Provides a time address for each video frame in hours,  
Time Code  
minutes, seconds, and frame numbers. Requires a SMPTE code generator to create. Some RTS™  
Systems audio equipment can be used to distribute SMPTE time code. Consult RTS™ Systems  
Engineering Department for details.  
Sound Variations in pressure (usually air) caused by vibrating bodies. Examples are air columns (pipe  
organs), strings (violins), vocal cords and larynxes (humans).  
Sound System A combination of transducers, amplifiers, and interconnections. A simple sound system could  
consist of a microphone or pickup and an amplifier and a headphone or speaker.  
Special List A special list is a means for a keypanel operator to talk and/or listen to several unrelated  
destinations using a single key. Special lists are useful for group call or zone paging. Special list  
members are defined in the intercom configuration software. Once a special list has been  
configured, it can be assigned to a keypanel key. A special list is a group of intercom ports that a  
keypanel operator can talk or listen to by activating a single key. Special lists are typically used  
for paging, all call, group call etc. Special lists have default names SL01, SL02 etc. These names  
can be changed using Other Alpha setup. You define the members of the special list using Special  
List setup. Once a special list has been set up, you typically assign it to a keypanel key using  
Keypanel setup. The keypanel operator can then activate the special list key to talk or listen to all  
members of the special list. IMPORTANT: Do not confuse special lists and Party-Lines. A  
special list is used when a keypanel operator needs to occasionally talk or listen to a group of  
intercom ports that are otherwise unrelated. A Party-Line is typically used when several users of  
non-keypanel devices (such as belt packs or camera intercoms) are engaged in a specific common  
activity and they need to talk and/or listen to each other all the time. Keypanels are almost never  
members of Party-Lines (although they can be). However, a keypanel key can be assigned to  
occasionally talk or listen to a Party-Line if desired. Just remember: Party-Lines are primarily set  
up for Party-Line members, with occasional access by keypanel operators, while special lists are  
set up exclusively for keypanel operators to talk or listen to several unrelated intercom ports. For  
specific information about special list setup, search for “special list” in AZ™EDIT help.  
SPL Sound Pressure Level. Sound is alternating pressure waves. Sound Pressures (amplitudes) are  
measured in pascals. The amplitudes can be converted into decibels using an equation. These new  
numbers are Sound Pressure Levels.  
Squawk (Versus A term to differentiate two kinds of point-to-point intercom. A squawk type intercom allows  
Matrix)  
instantaneous momentary communication. The Model 810 in the “squawk” configuration  
(momentary buttons only) is a pure squawk system. The Model 810 is available in a “matrix”  
configuration (alternate action buttons, electrically the same).  
Stacked Key See the descriptions for talk level, talk level 2.  
Stereo Recording, transmitting or reproducing a sound source with two or more separate sound pickups.  
The recording has two or more separate channels.  
Studio Camera Used both in studios and remote locations. A heavier, larger camera mounted on a pedestal or  
other suitable mount. Generally has better quality pictures than a lighter, smaller field camera.  
Studio Talkback A loudspeaker system from the control room to the studio. Also called SA (Stage Announce, or  
Studio Announce).  
Supra Aural A headset where the earpieces rest on the ear.  
Headset  
Supercardioid A microphone pattern with a maximum rejection at 125 degrees off axis. A compromise design  
between the cardioid and the hypercardioid.  
Switcher Person who operates the switcher to switch the video; the switching device itself.  
(usually the  
Technical  
Director)  
System 1. An assemblage or combination of things or parts forming a complex or unitary whole. 2. The  
structure or organization of society, business, or politics. 3. The interrelationship of a collection of  
interdependent elements and processes.  
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T
Talent Collective name for all performers and actors who appear regularly on television.  
Talk Level 1 Talk level 1 is the normal talk key assignment. This is the assignment that normally appears in the  
alphanumeric display (on keypanels so equipped). You may add a talk level 2 assignment to  
activate a second device along with talk level 1.  
Talk Level 2 Talk level 2 is used with stacked talk keys. A stacked talk key activates two types of  
communication at once. For example: a stacked talk key could simultaneously activate audio  
output to a transmitter and key the transmitter using a relay. The audio output is called the level l  
assignment and the relay is called the level 2 assignment.  
Tally An intercom’s tally usually identifies a calling party to a called party, tally can also indicate a call  
waiting.  
Telco Abbreviation for Telephone Company. Refers to communication lines owned and operated as part  
of a standard telephone system.  
Tone Signaling An audio tone distributed on the intercom line (may be associated with light signaling). This tone  
is often used for alerting an operator.  
Transducer In sound, a device that converts acoustic energy to electrical (e.g.: microphone) or vice versa  
(e.g.: loudspeaker).  
Transformer Audio transformer: a device that can isolate two circuits, and, in addition, match impedances, step  
up or down voltages or currents. A microphone transformer can be used to optimize the signal to  
noise ratio of a microphone preamplifier combination. Power transformer: a device that isolates  
electronic circuitry from a direct connection with the power line, and provides power at a  
convenient voltage for the electronic equipment (usually rectified and filtered first).  
Transient In acoustics, a sudden change such as that from a percussive instrument (drum or piano). In  
electronics, a sudden change such as a stepped signal or spiked signal.  
Transient See Distortion.  
Intermodulation  
Distortion  
Transient Equipment needs to be designed to be damage proof from power line transients. Good audio  
Response  
equipment needs to handle well signal transients that occur normally. Transient handling may  
require headrooms of 20 to 60 decibels. The headphone amplifiers used in RTS™ Systems  
intercoms generally have good transient handling capability.  
Trunking Trunking is a method of interconnecting two or more independent intercom systems. The  
connection is accomplished by reserving one or more audio ports in each of the intercom systems  
for use as audio links between the systems. A special device, called a Trunking Master Controller,  
is required to control access and usage for the trunked intercom ports. A configuration utility,  
called CStrunk, is used to set up the Trunking Master Controller.  
Two-Wire A communications system where the path is the same for both talk and listen. In electrical  
pathways there are, in fact, two wires (one path). Two-wire systems can be two- wire balanced or  
two-wire unbalanced.  
Two-Wire Two-wire balanced is similar to two wire unbalanced except that neither conductor is tied to  
Balanced  
circuit common. Circuit common is either tied to a transformer center tap, or is an electrical center  
point, or not tied at all.  
Two-Wire A two-wire system that uses a circuit common and one additional conductor for a pathway. This  
Unbalanced  
system allows easy addition of DC power as well. Although a balanced two wire system has less  
sensitivity to outside electrical interference.  
Unbalanced A communications line that uses circuit common or “ground” as a return path. In the case of  
Line  
intercom systems, in general, an unbalanced line is more susceptible to noise interference. But  
practically speaking, a low impedance unbalanced line (200 ohms) works well in the real world,  
and has the added advantage of being able to operate on just two wires, carrying the DC power,  
the full duplex audio signal, the 20.000 kilohertz call light signal, and the 24.000 kilohertz  
microphone reset signal. Many installations have been previously wired for telephone operation  
and the two wire intercom works on these pairs. A special “golf’ system application of the TW  
System has the advantages of the TW system and balanced line operation. A standard TW power  
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supply operates a string of belt pack or other user stations in an isolated, balanced mode. The  
balanced system is transformer coupled into the regular unbalanced system.  
V
V
The symbol for volt.  
VA The symbol for volt-ampere. A volt-ampere describes the demand on the power line without  
regard to power factor or true power. This figure is more helpful in determining the maximum  
load on a circuit, that has a given ampere rating.  
Voltage The term for electrical potential of electromotive force.  
Voltage Drop See IR drop.  
VU Volume Units.  
VU Meter Used to show the relative levels of signals. A change of one VU is a change of one dB. VU meters  
have their 0 VU point referenced to different levels. This level may be 0 dBm, +4 dBm  
(Recording Industry), +8 dBm (Broadcast Industry). In addition, correct calibration is further  
involved. The VU Meter has certain characteristics tailored for monitoring sound. Generally  
speaking the audio peaks are 10 dB above the indications shown on a standard VU meter due to  
the lag of the meter. Some VU meters are combined with peak reading meters. Levels stated in  
“VU”s generally apply to program material. Readings in dBm generally apply to a steady state  
sine-wave.  
W
W
The symbol for the unit of power, the watt.  
Watt A unit of electrical power. One watt is the power delivered by one volt at a current of one ampere  
in a DC circuit, and one volt at one ampere with a phase angle of 0 degrees in an AC circuit.  
Wave Form A graphical representation of a varying quantity. The x (horizontal) axis usually represents time  
and the y (vertical) axis usually represents amplitude, energy, or power.  
White Noise Equal noise energy per hertz.  
Windscreen A microphone cover designed to reduce extraneous noises caused by gusts of wind. Also useful  
for reducing pop from speech plosives such as “b”, “p”, and “t”.  
Wet Line An intercom or telephone line that carries both audio and DC voltage / current. As opposed to a  
dry line that carries only the audio.  
X
Y
Z
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INDEX  
Numerics  
A
ADAM™ (including ADAM™ CS and Zeus™) Intercom Cable Connections . . . . . . . . . . . . . . . . . . . . . . . 67  
B
C
Camera Isolate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6  
Cascaded Trunking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76  
D
I n d e x 1  
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digital four-wire control station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114  
E
effective radiated power (ERP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98  
F
G
H
I
IFB Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124  
Interfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77  
Interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100  
2
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K
L
Large Studio or Mobile Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123  
limiter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14  
M
modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97  
N
O
P
PAP951 Program Assign Panel and UIO256 GPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122  
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R
S
Simple Matrix System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2  
Special List or Group Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54  
Studio Announce and Dressing Room Paging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125  
T
4
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Typical ADAM™ Matrix Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62  
Typical single channel belt pack headset user station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11  
U
Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124  
V
W
Y
Z
I n d e x 5  
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