"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