wrote in message
link.net...
54-60 mHz carrier at 55.125

(55.125 * 2) + (2 * 10.7) = 131.65
(55.125 * 2) + 10.7 = 120.95

76-82 mHz carrier at 77.125

(77.125 * 2) - (2 * 10.7) = 132.85

225.525 (digital? ham repeater?) - 77.125 - (2 * 10.7) = 127.00.

Just playing...

If it's intermittent then are there any ham repeaters or other
comms repeaters in the area?

And, two, a 'directional' antenna.

If an AM radio station was causing the problems and you
wanted to know which mast was causing it, you could tune
in the ADF and see where the needle points! :-)

If the source is outside the plane, you're conclusively dealing with front
end overload intermodulation interference.

Unless you're getting in-band interference from outside the plane,
such as harmonics, intermod from rusty bolts or other transmitters
as others have mentioned, etc.

If that's the case:
1) high-Q bandpass filtering, to eliminate the out-of-band interference
sources.
wouldn't work. I'd say it was worth a try first though, relatively
easy to stick in-line with an antenna and it would get rid of most
of the out of band signal straight off. Not to leave the filter there
but just as a trial to see if the interference is in-band or out-of-band.

Paul