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My Experience with the Radio Shack
Antenna Mounted Amplifer
I know that from time to time many people on various newsgroups and email lists ask the question
"what pre-amp will improve my scanners reception?". The typical answer is "they don't
work, they'll overload your radio". And usually these comment were from people who have
NEVER tried one in their life.
I too have asked the question and after getting either no response or negative comments without
any specific information on what was tried I figured I'd experiment myself regardless of
what the nay-sayers kept harping. After searching the net I couldn't find any pre-amps
specifically for the frequencies which were of interest to me. That would be 108-136,
138-144, and 225-400 MHz ranges. So I went the next best route. Buying an antenna
mounted TV amp. Radio Shack as two antenna mounted amps, model # 15-1108 and model
#15-1109. Warning: Radio Shack also has inline TV signal amps and distribution amps,
however these will not work as well for scanning as they will amplify noise picked-up
along your coax as well as the signal.
Radio Shack 15-1108
Radio Shack 15-1109
At the time of this writing the #15-1108 is $41.99 and provides (according to RadioShacks own
specs) 20 dB gain UHF-TV and 25 dB gain VHF-TV. It has a 10 dB adjustment to help prevent
overload and also is equipped with a FM trap which can be switched off. The #15-1109 is $64.99.
RadioShack's specs simply say "up to 30 dB gain, VHF-TV, VHF-FM, UHF-TV". For the purpose of my
experiment I purchased the #15-1108 amp.
I installed this amp on an Antennawarehouse ScannerBeam. This amp consists of three parts,
the antenna mounted amp and the control/power unit. One plus here is that it has a real
120 Volt Plug, NO WALLWART that takes up 2 electrical outlets! That's a big plus in my book
as I have over 20 wallwarts for all my radio equipment! The control/power unit has TV F type
connectors so I did buy some BNC/F adapters from RadioShack to make coax connections easier.
As a compairison I used the ScannerBeam/Amp setup against a Create Log Periodic mounted at 30'
(the ScannerBeam was only at 18'. The Create (non amplified) was feeding a BC 780 scanner
and the ScannerBeam (amplified) was feeding another BC 780 so I could do side by side tests.
My first test was in the VHF and UHF TV ranges, as that was what the amp was designed for.
I figured if I couldn't see an improvement here there was no use in continuing. Well with both the
Create and ScannerBeam pointed in the same direction I let the BC 780's search the entire TV band
(both VHF and UHF). On every channel the non-amplified antenna picked up the same station the amplified
antenna picked up and was at least 1 (sometimes 2) s-meter bars higher in strength. The audio quality
was as good if not slightly better as well. The amplified antenna also picked up 3 other stations which
the non amplified antenna couldn't receive. Remember that the non-amplified antenna was mounted 12 feet
higher! For these test I left the FM trap on. If I tuned the BC 780 to a VHF TV
frequency and opened the squelch I could hear the scratchy sound of an FM station.
So without question there was a slight amount of FM overload as a result of the amp which
even its own FM trap couldn't attenuate fully. It wasn't enough to cause ill effects to frequencies
which there were true signals, even weak sigs (which the Create antenna couldn't receive) The addition
of a quality FM trap or bandpass filter for the bands you're interested in might eliminate this problem.
I've ordered some filters from Stridesberg which I'll experiment with later.
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shack and antennas.
The next experiment was the 2 meter ham band. Again, every repeater the non-amplified antenna
received the amplified antenna received as well and in most cases better. There was one repeater
(not sure if it location) which the non-amplified antenna could not receive where the amplified
antenna was able to receive a readable signal.
After testing the 2 meter band I went to the Civil Air Band. A good test case I used here is the
Sanford, FL tower on 120.3000. This tower is located about 30 miles away. Before adding the
amp to the ScannerBeam the ScannerBeam could not receive the ground side of comms on this freq.
The Create usually can (remember the Create is mounted 12' higher). With the amplifier turned
on I pointed both beam antennas at the tower. Both antennas now could receive the ground side
of the tower comms! Both were receiving it with equal quality. There is one strange think I
must note here. On the BC 780 connected to the amplifed antenna, the S-meter would be at
between 3 bar and full scale even without anyone transmitting on the monitored frequency.
I would open the squelch and only hear the normal amount of static, so it didn't appear to be
overload from a FM station. It will be interesting to see if this goes away once I add a
commercial quality FM trap. This "full-scale s-meter" situation also occurred in the 225-400 MHz
MilAir Band. It didn't appear to effect scanning, the squelch acted normally regardless of the
full-scale s-meter deflection.
As my final test I monitored many military air freqs. It seemed that in every case the
amplified antenna once again preformed as well as the other antenna. Again remember the
other antenna (non amplified). is mounted 12' higher, 12' makes a world of difference for
MilAir monitoring. Also the non-amplified Create Log Periodic is advertised to have 11-13 dB
gain where as the ScannerBeam only 6 dB gain in the tested frequency ranges.
The amplified antenna setup isn't perfect. You're going to get some FM Overload and some
Intermodulation problems (mixing of other signals). I do have some intermod problems do
to some paging systems in my area. I believe that the addition of a commercial grade filters
will reduce if not eliminate this problem. Even before trying intermod filters I've found
the problem to be manageable and not be nearly as bad as we are lead to believe by many people
on the various newsgroups. Again you need to remember the people making this comments are
usually people who have never tried this themselves!
As a side note you'll see in one of my pictures it appears I'm using a "roof mount antenna tripod"
as a temporary antenna stand. I've found that the "EASY-UP" Antenna Tripods make great
antenna stands when using 10-20' of antenna mast. As you can see I just have these setting
on the concrete patio around our inground pool. On each of the three legs I have 2 concrete
patio stones to hold the stand in place during wind. The ScanTenna has seen wind gusts over
40 MPH and hasn't moved. So far the ScannerBeam has seen 20 MPH winds with no ill effects.
When we get storms during the hurricane season its very easy to lay these antennas on the ground
until after the storm passes. Unless there are forecasts for 60+ MPH winds I have no plans on
laying down these antennas. My main antenna, the Create Log Periodic, is mounted on a 30'
telescoping mast and is attached to a cement block chimney. Even in 40 MPH winds it stays
rock solid. After running out of room on the chimney for more antennas I had to come up with
another idea. The EASY-UP Tripods was my solution. They are available from AES-Ham.com and
other sources in the net.