I'm guessing that because of all the new B.S. concerning Homeland
Security, the airport probably has a fence around it with a security
coded gate control so that non-pilots can't get onto the field...

Scott


John S. wrote:




Rather than re-broadcasting the signal why not try something simpler.
Just set up an Airport Traffic room within the airport and pipe the
audio in. Hang some old pictures and other memorabilia of the airport
on the walls to make it interesting.

Scott wrote:
I'm guessing that because of all the new B.S. concerning Homeland
Security, the airport probably has a fence around it with a security
coded gate control so that non-pilots can't get onto the field...

Scott


John S. wrote:




Rather than re-broadcasting the signal why not try something simpler.
Just set up an Airport Traffic room within the airport and pipe the
audio in. Hang some old pictures and other memorabilia of the airport
on the walls to make it interesting.


Most airports have a lounge of some kind....

All,

Thanks for all the suggestions, advice and information. I learned a lot
about VHF that I didn't know. Should have stayed with it way back when I
almost finished my "Novice" amateur license (couldn't manage the Morse code
part -- I guess that gives away my age).

Fred nailed it, although by the time I saw his note, I'd solved the problem.
After relocating the receiver as far away as I could (60 feet, given the
limitation of where the units needed to be and sources of power) which
didn't really help, I tried some simple filters, etc. During the course of
this, someone keyed a mike while I had the antenna disconnected, and it
worked fine with no antenna connected! A bit more experimentation indicated
that the 120.6 interference dropped out completely while the desired 123
signal could still be picked up from five miles away if I left the short
coax jumper inside the box from the receiver to the antenna disconnected at
the antenna end. I'm not sure I fully understand why I still get a pretty
robust signal this way, but I guess enough 123 MHz RF is leaking in from the
bare antenna or all the other wiring. Since the radio traffic of interest
is mostly local planes near the airport or in the traffic pattern, a five
mile radius is probably more than adequate, and this is certainly the
cheapest solution.

I will also look into the regulations about rebroadcasting non-commercial
radio signals. The transmitter satisfies the part 15(IIRC?) FCC reg about a
100-foot reception limit, but I thought the rules about rebroadcasting were
to prevent commercial rebroadcasting. The 100 foot limitation will keep
all reception on the airport grounds, but I will do some more research on
this. Thanks.

As far as an area inside the building where people can listen to the radio
is concerned, we already have that. This project is for the people who sit
in their cars in the parking lot and watch the planes on their lunch hour,
etc. We get quite a few of these. Anything that improves relations with
the general public should help alleviate some of the problems we have with
the neighbors. I still can't understand how anyone can buy a house near an
airport, and then feel that they have a right to complain about airplane
noise. The airport has been there since 1946, but that's another issue.

Again, thanks for all the help.

--
Bob (Chief Pilot, White Knuckle Airways)


"Fred McKenzie" wrote in message
...
In article , "Bob Chilcoat"
wrote:

Unfortunately, while this setup worked perfectly at home well away from
the
airport, we have an Automatic Weather Observation Station (AWOS)
transmitting continuously on 120.60 MHz only 50-60 feet from the place I
need to site the receiver. Even though this is only a 5 Watt
transmitter,
it overloads the front end of the receiver. As soon as anyone keys on
123.00 and the automatic squelch is triggered, all you hear is the AWOS
recording.

Bob-

By now you have probably solved your problem. If not, someone else
suggested that you insert attenuation in the Sony's antenna lead. I think
that approach is most likely to produce the results you want.

If you were to replace the Sony's antenna with a dummy load, there may
still be sufficient signal bleeding into the radio to make your system
work. The interfering signal would also bleed into the radio, but at such
a low level that the Sony's tuned circuits ought to be able to handle it.

If even this does not solve the interference, you may find the problem to
be audio rectification inside the 88.1 equipment, perhaps in the
oscillator stage!

Please keep us informed of what it takes to make it work.

73, Fred, K4DII

"Bob Chilcoat" wrote in message
...
... a rather old but serviceable Sony digital air band receiver
...piped the audio out to an FM microwatt transmitter.
... visitors ...can listen on their car radios on
.... Advisory Frequency (CTAF), which at our airport is 123.00 MHz (AM).
...5 Watt transmitter,
it overloads the front end of the receiver. As soon as anyone keys on
123.00 and the automatic squelch is triggered, all you hear is the AWOS
recording. Bob (Chief Pilot, White Knuckle Airways)

My turn...

Lots of really good ideas here. Make sure it is the Sony antenna that is
picking it up...

1- The stub-trap idea may work with some large number of odd-quarter waves.
As you stack more odd multiples of quarter waves on (extend the shunt trap
length), the dips get closer together and as a result the peak-to-null
distance shrinks. A stub that is 21 quarter waves long has peaks and nulls
very close together (you could calculate this). Of course the dips will be
less deep due to cable loss. This may make it easier to get the desired
"Pass / Null" response. You need to make sure the signal is getting into
the antenna and not the receiver itself. The 2.4 Mc spacing is quite close.

NEW IDEA:
2- Try tuning it on the image (for your 123 Unicom frequency). You will
probably need to do this away from the airport . You should hear the Unicom
in two places on the dial spaced _TWICE_ the IF frequency away. These
radios usually have pretty wide front ends There may be a schematic inside
the radio to help determine this. If the IF is 0.455, the image is 0.910
away. This radio probably uses low side injection meaning the LO is below
the 123 by 0.455. Therefore you must tune the radio 0.910 HIGHER than 123.
This places the on channel further away from the 120.6 AWOS. Not knowing
the IF, you have to hunt.
-Maybe doing this _AT_ the airport will yield a tuning that fixes it.
Just try "tuning around".
Related idea, you could also figure out where the RF stage stuff is in
the radio and de-tune it upward to get more attenuation at 120.6, but if
that works, then just some attenuation in the antenna line may work as well
and be easier.

3- Put the radio FAR away, but run the audio in some small coax to the 88.1
closer to the visitors.

4- I like the "cross Polarization" idea. Do a light saber thing with the
Sony antenna. There may be a sweat spot that just might get the levels down
and fix the IM or whatever is going on..


Mike T. Use the airport receiver...

Sounds good, but they probably don't want you messing with it.... and what
about the airport's transmissions...

5- HOWEVER, how about simply a microphone right next to this receiver and
within earshot of the airport's microphone---ON the 88.1 Tx ?? You may
hear other stuff in the FBO, but it may be ok too...

Related... I have a little thing I plug into my dual band rig speaker
output and it transmits the audio to my car FM radio. They're made for
listening to battery operated CD players in your car.

73, Steve, K;9.D,C'I

Around here, most "lounges" or "Terminal buildings" are inside the
fence, so the original problem remains that limits non-pilots (or pilots
who happen to be driving by a strange airport) from gaining access to
the field.

Scott


John S. wrote:

Scott wrote:

I'm guessing that because of all the new B.S. concerning Homeland
Security, the airport probably has a fence around it with a security
coded gate control so that non-pilots can't get onto the field...




Most airports have a lounge of some kind....