THE ‘LOGI’
LOG PERIODIC
ANTENNA
Ramsey Electronics Model No.
LPY915
Constructed on rugged FR-4 material, it requires no tuning and
has no fragile antenna elements to break or twist! Covers the
entire 900 to over 2,500 MHz frequency range.
Why settle for any old antenna… this little baby “compresses”
the signal into a powerful beam that is 4 times more powerful in
the direction you desire!
•
•
•
•
•
Easy hookup to your Receiver or Transmitter
Small thin size with excellent broadband performance
Solid 6 dB gain from 900 to over 2,000 MHz!
VSWR less than 2:1 - great for transmitters up to 10 Watts!
Easily mounted by itself or makes a great feed for reflector
dishes
• Construction ideas for a wideband corner reflector and a
‘grid’ reflector dish are covered in the manual!
• Very directional - ideal for point-to-point links
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Ramsey Publication No. MLPY915
Price $5.00
KIT ASSEMBLY
AND INSTRUCTION MANUAL FOR
Logi
LOG PERIODIC
ANTENNA
TABLE OF CONTENTS
Introduction.................................4
Antenna Description ...................4
Standard Hook-up ......................5
Low Frequency Modification .......7
Building a Corner Reflector.........7
Building a Reflector Grid.............9
LPY915 Return Loss Plot ...........10
Return Loss vs. VSWR Chart .....10
Warranty.....................................11
RAMSEY ELECTRONICS, INC.
590 Fishers Station Drive
Victor, New York 14564
Phone (585) 924-4560
Fax (585) 924-4555
LPY2 • 3
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INTRODUCTION
This small log periodic antenna, which we call the ‘Logi’, is ideal for getting the
maximum performance out of any UHF to low frequency microwave wireless
system. Its directional properties “compresses” the signal into a powerful beam
that is 4 times more powerful in the desired direction. It is the ideal antenna for
scanners, wireless LANs, and other wireless devices. Its directional properties
make it exceptionally well suited for point-to-point links! The units small size
and wide bandwidth also make it ideal for feeding reflector antennas, such as
the easily constructed corner reflector or grid that are discussed later in the
manual.
ANTENNA DESCRIPTION
To start with, what is a log periodic antenna? The seeming simplicity of the log
periodic antenna belies the remarkable features of the design. It uses a
common transmission line to alternately feed a group of 1/4 λ dipoles that are
strung together. These antennas together display excellent radiation qualities
over a wide range of frequencies as well as relatively uniform input impedances
and good VSWR characteristics. While the log periodic design has been
around since the late 1950’s it has now been discovered to be at the cutting
edge of antenna development.
Looking at the physical layout of a
log periodic antenna, one would see
that it is comprised of multiple
elements working together to provide
a wide bandwidth of usable
frequencies. The active (radiating or
receiving radiation) portion of the
antenna effectively shifts with
Feed
Point
frequency as one stage becomes
‘more resonant’ than the next. The
lowest operating frequency is
determined by the longest element
and the highest operating frequency
is set by the shortest element. As the frequency of the transmission (or
reception) increases, the active region of the antenna shifts forward to the
shorter 1/4 λ dipole elements or vice versa as the frequency decreases.
Obviously then the ‘secret’ for proper operation must lie in the length and
spacing of the antenna elements. These and other factors must be carefully
chosen to cover the desired frequency range for the antennas’ application.
Instead of forcing you to figure out all the math and spend hours experimenting,
the creation of the Logi antenna (for frequencies between 900 and 2600 MHz)
comes to the rescue!
LPY2 • 4
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STANDARD HOOK-UP
Normal applications are well suited by the default performance of the unit
without the need for cumbersome reflective elements. The standard wiring
configuration is simply to use the Logi as the complete antenna and merely add
a means of connection for your radio. The easiest method to interface your
antenna and radio is through the use of a coaxial cable with a pre-mounted
connector. Standard RG-58 and a BNC connector are often used by ‘scanner
buffs’ to quickly and easily monitor the airwaves. Other types of coaxial cable
such as RG-142, .141 and .085 semi-rigid will also provide you with a good low
loss connection as well as excellent high frequency characteristics.
Let’s take a look at the circuit board for a moment to
become more familiar with its layout. The bottom side
Via
Bottom
Top
is the ‘ground’ connection and is labeled with the
designers call sign “WA5VJB”. Notice that the via (the
small plated through hole) near the narrow front of the
board is not directly connected to the center trace on
the bottom side. It is directly connect on the top side
however.
ˆ 1. Scrape off the protective solder mask coating on the bottom side center
ground trace with a razor. Only remove the mask along the center trace,
not the perpendicular elements. Be careful not to accidentally cut them
while removing the mask. This is where you’ll attach the ground shield of
your coax.
ˆ 2. Tin the center ground trace you just scraped with a thin layer of solder.
This will make mounting the ground conductor easier in a moment.
ˆ 3. Measure back 4 3/4” from the open end of your coax and remove the
outer protective sheath (if applicable) to expose the ground conductor.
ˆ 4. Using a small pair of wire cutters (or a razor for the semi-rigid coax
variety), clip away a 1/2” of the ground braid from the same open end to
expose the inner dielectric layer.
ˆ 5. You now need to trim away the end 7/16” of the inner dielectric layer
giving access to the center conductor. Position your razor for the cut and
roll the coax on the table top to slice through the entire circumference
(Don’t mark-up the wife’s table!!). The end goal is to leave about 1/16” of
the dielectric between the ground conductor and the
center conductor.
ˆ 6. Carefully tin (solder the braid wire together to
keep it from fraying) the first 1/4” of the ground braid.
Be careful not to melt the dielectric with too much
heat.
4 1/4"
7/16"
1/16"
LPY2 • 5
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ˆ 7. From the bottom side, slide the center conductor of the coax through the
open via at the front of the circuit board.
ˆ 8. Gently bend the remaining cable to mount flush along the tinned center
ground strip.
ˆ 9. Look closely at the ground
Soldered Coax Positioning
conductor and make sure there are
no stray braid wires hanging
around. They can short out the
coax near the via when you solder
it in place rendering your antenna
useless!
ˆ 10. Solder the length of the ground
conductor to the circuit board along
the tinned center ground strip. Be
careful at this point not to overheat
the ground conductor and melt the
dielectric layer. Spot soldering the
ground braid at the element junctions works well to avoid overheating the
coax.
ˆ 11. It’s time for the last connection! Solder the center lead of the coax in
place on the top side of the circuit board where it passes through the via.
ˆ 12. Visually examine the junction you just soldered and again make sure
the center feed of the coax is not shorted to ground.
Note that using an ohmeter to check you LPY915 antenna for shorts will not
work. By default, the top and bottom layers are connected together by small
traces near the end of the board. Normal operation requires these traces to be
left intact. An optional low frequency modification for improved performance
near 825 MHz will be discussed next.
Time to start playing! Interface the other end of the coax feed with your radio
and enjoy the benefits of a broadband
Final Installation View
directional antenna!
LOGI LOW FREQUENCY MODIFICATION
If your radio system requires DC isolation
or you plan to use your Logi below 900
MHz, the small connecting traces near the
rear of the antenna should be cut. By
removing these traces you can extend the
effective frequency range down to 825
MHz. You will however wind up with some
‘lumps’ in the matching response on the
LPY2 • 6
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high frequency end.
BUILDING A CORNER REFLECTOR
Corner reflector antennas have long been used
by the Military and Radio Amateurs for high
forward gain applications like field data links.
Using a properly sized 90° angle corner reflector
will typically give you a 10 dB gain or higher over
that of a stand alone dipole antenna. The
construction of a traditional corner reflector is
very simple. Two plates are connected at a 90° angle with a feed element,
usually a dipole, positioned along the vertex at the angular focal point of the
plates. The dimensions of the reflector plates are luckily not critical (within
reason of course) and the frequency characteristics are much better than most
other parasitic arrays with the same gain rating. One drawback of the normal
corner reflector arrangement is the fact that the active (radiating or receiving)
element is usually a narrow bandwidth dipole. In our case, we suggest using
the ‘broadband’ Logi as the feed element. This gives you the same corner
reflector benefits but without the normal narrow bandwidth limitations!
With the wealth of information available today on the Internet, countless
articles and design schemes can be found covering the construction of corner
reflectors. The main difference from the norm is the use of the Logi as the
main element versus a simple dipole. The following diagram gives a few basic
dimensions for an experimental corner reflector. The main points to key in on
are the base reflector size and the element (the Logi) placement for proper
broadband coverage.
Different types of materials can be used to form the reflector plates. Any type
of perforated aluminum or copper sheet will work well. Small holes in the
material help to cut down on wind resistance. The overall reflector length and
width sizes should be chosen to properly work at the lowest frequency you
plan to use. In the case of the Logi, 900 MHz was used to calculate the
dimensions. A gain of 10 dB can be obtained with a reflector side length of
one wavelength. A two wavelength reflector can be used to achieve upwards
of 12 dB gain! It just means you’ll have a bit more wind resistance to factor in.
The positioning of the Logi as the active element must also take into account
the frequencies you’ll be dealing with. Thankfully, the physical layout of the
circuit board takes care of this for us automatically! The narrow front end of
the board should be placed so that it points into the vertex of the reflector
plates. Rotate the board so that it lines up directly with the seam created by
the two plates. This allows one side of the Logi to collect (in receive mode) or
emit (in transmit mode) the electromagnetic energy from one plate to one side
of the active element. If the Logi is turned 90° so that it does not line up in
LPY2 • 7
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parallel with the seam, the antenna will not function properly.
The boom length that positions the Logi at the focal point of the reflector is
also critical factor. This will require a bit of trial and error to get things just
right. Use a piece of PVC pipe (1/2” to 7/8” will work well) with a slot cut in the
end just big enough to wedge the entire Logi in place. The narrow front edge
of the circuit board should be positioned between 1.5” to 3” from the seam
formed by the two reflector plates. PVC couplers can be mounted in the vertex
of the reflector to allow you to slide the boom in and out while testing. Once
the optimal position of the Logi is set, tighten the coupler and your ready to go!
BUILDING A REFLECTOR GRID
Building a reflector grid antenna as a home-brew project is a little harder then
the corner reflector. It would be very difficult to achieve the proper parabolic
shape for the reflector by banging on an old BBQ grill! The best way to insure
your antenna will function the way you want is to use a pre-fabricated dish.
There are a few different dishes that are easy to get and very affordable. We
10.0" -12.0"
°
90 Corner Reflector
12.0"
Insert the Logi
narrow end first.
Cut a slot into
the PVC boom.
Logi front edge placed
1.5" to 3" from vertex.
LPY2 • 8
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experimented with the ISM19R and ISM24R and found that they work
wonderfully with the Logi!
Look at the how the Boss used a piece of PVC and a few couplers to form a
boom. He cut a slot in one end of the PVC pipe to hold the Logi antenna in
place. Then he used a nylon wire tie at the end of the boom to squeeze the
slotted pipe like a vise! Wow!!! Simple to make and highly effective!
LPY915 mounted on a Grid Reflector
If you plan to do the same,
here is a quick shopping list:
LPY915 mounting Boom for a Grid Reflector
ˆ 1 Ramsey ISM19R
or ISM24R (or
equivalent)
ˆ 1 16 1/2” piece of
1/2” PVC pipe
ˆ 1 1/2” to 1” PVC
coupler (non
threaded)
ˆ 1 3/4” to 1” PVC
coupler (threaded on the male 3/4” side only)
ˆ 1 can of PVC cement
ˆ 3 4” minimum nylon wire ties
LPY2 • 9
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LPY915 RETURN LOSS PLOT
RETURN LOSS VERSUS VSWR - CONVERSION CHART
Return Loss VSWR
(dB)
Return Loss VSWR
(dB)
Return
Loss (dB)
VSWR
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
17.391
8.724
5.848
4.419
3.570
3.010
2.615
2.323
2.100
1.925
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0
1.785
1.671
1.577
1.499
1.433
1.377
1.329
1.288
1.253
1.222
21.0
22.0
23.0
24.0
25.0
30.0
35.0
40.0
50.0
60.0
1.196
1.173
1.152
1.135
1.119
1.065
1.036
1.020
1.006
1.002
The LPY2 offers exceptional wide band characteristics from 900 MHz to 2.6
GHz and can be used as a Receive or Transmit (10 Watts max) antenna!
Standard guidelines for antenna systems:
•
•
Receiver Antenna Match >
Transmitter Antenna Match > VSWR = 2.0 : 1.0 or better
VSWR = 3.0 : 1.0 or better
LPY2 • 10
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The Ramsey Kit Warranty
Please read carefully BEFORE calling or writing in about your kit. Most problems can be
solved without contacting the factory.
Notice that this is not a "fine print" warranty. We want you to understand your rights and ours too!
All Ramsey kits will work if assembled properly. The very fact that your kit includes this new manual
is your assurance that a team of knowledgeable people have field-tested several "copies" of this kit
straight from the Ramsey Inventory. If you need help, please read through your manual carefully.
All information required to properly build and test your kit is contained within the pages!
1. DEFECTIVE PARTS: It's always easy to blame a part for a problem in your kit, Before you
conclude that a part may be bad, thoroughly check your work. Today's semiconductors and passive
components have reached incredibly high reliability levels, and it’s sad to say that our human
construction skills have not! But on rare occasions a sour component can slip through. All our kit
parts carry the Ramsey Electronics Warranty that they are free from defects for a full ninety (90)
days from the date of purchase. Defective parts will be replaced promptly at our expense. If you
suspect any part to be defective, please mail it to our factory for testing and replacement. Please
send only the defective part(s), not the entire kit. The part(s) MUST be returned to us in suitable
condition for testing. Please be aware that testing can usually determine if the part was truly
defective or damaged by assembly or usage. Don't be afraid of telling us that you 'blew-it', we're all
human and in most cases, replacement parts are very reasonably priced.
2. MISSING PARTS: Before assuming a part value is incorrect, check the parts listing carefully to
see if it is a critical value such as a specific coil or IC, or whether a RANGE of values is suitable
(such as "100 to 500 uF"). Often times, common sense will solve a mysterious missing part
problem. If you're missing five 10K ohm resistors and received five extra 1K resistors, you can
pretty much be assured that the '1K ohm' resistors are actually the 'missing' 10 K parts ("Hum-m-m,
I guess the 'red' band really does look orange!") Ramsey Electronics project kits are packed with
pride in the USA. If you believe we packed an incorrect part or omitted a part clearly indicated in
your assembly manual as supplied with the basic kit by Ramsey, please write or call us with
information on the part you need and proof of kit purchase.
3. FACTORY REPAIR OF ASSEMBLED KITS:
To qualify for Ramsey Electronics factory repair, kits MUST:
1. NOT be assembled with acid core solder or flux.
2. NOT be modified in any manner.
3. BE returned in fully-assembled form, not partially assembled.
4. BE accompanied by the proper repair fee. No repair will be undertaken until we have received
the MINIMUM repair fee (1/2 hour labor) of $25.00, or authorization to charge it to your
credit card account.
5. INCLUDE a description of the problem and legible return address. DO NOT send a separate
letter; include all correspondence with the unit. Please do not include your own hardware
such as non-Ramsey cabinets, knobs, cables, external battery packs and the like. Ramsey
Electronics, Inc., reserves the right to refuse repair on ANY item in which we find excessive
problems or damage due to construction methods. To assist customers in such situations,
Ramsey Electronics, Inc., reserves the right to solve their needs on a case-by-case basis.
The repair is $50.00 per hour, regardless of the cost of the kit. Please understand that our
technicians are not volunteers and that set-up, testing, diagnosis, repair and repacking and
paperwork can take nearly an hour of paid employee time on even a simple kit. Of course, if we find
that a part was defective in manufacture, there will be no charge to repair your kit (But please
realize that our technicians know the difference between a defective part and parts burned out or
damaged through improper use or assembly).
4. REFUNDS: You are given ten (10) days to examine our products. If you are not satisfied, you
may return your unassembled kit with all the parts and instructions and proof of purchase to the
factory for a full refund. The return package should be packed securely. Insurance is
recommended. Please do not cause needless delays, read all information carefully.
LPY2 • 11
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LPY915 LOG PERIODIC ANTENNA
Quick Reference Page Guide
Introduction ........................................................4
Antenna Description...........................................4
Standard Hook-up..............................................5
Building a Corner Reflector ................................7
Building a Reflector Grid ....................................9
LPY915 Return Loss Plot...................................10
Warranty ............................................................11
REQUIRED TOOLS
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•
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Soldering Iron
Ramsey WLC-100,
Ramsey RTS12
Ramsey RTS05
Ramsey RTS04
Thin Rosin Core Solder
Needle Nose Pliers
Small Diagonal Cutters
<OR> Complete Soldering Tool Set RS64-2801
ADDITIONAL SUGGESTED ITEMS
•
•
•
Optivisor Magnifier Headband
Holder for PC Board/Parts
Desoldering Braid
Ramsey OPMAG
Ramsey RTS13,
Ramsey RTS08
TOTAL SOLDER POINTS
Price: $5.00
Ramsey Publication No. MLPY915
Assembly and Instruction manual for:
2
ESTIMATED ASSEMBLY
TIME
RAMSEY MODEL NO. LPY915
Beginner ........... 1.00 hrs
Intermediate...... .50 hrs
Advanced.......... .25 hrs
RAMSEY ELECTRONICS, INC.
590 Fishers Station Drive
Victor, New York 14564
Phone (585) 924-4560
Fax (585) 924-4555
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