RF interference issue again (esp. for E Drucker and Jim Weir and other RF wizards)

On 4 Nov 2003 06:01:30 -0800, (Snowbird)
wrote:

wrote in message .. .

What you have here is a pretty classic case of intermodulation
interference.

Elliot, given what we did, is there a way to pinpoint what
signals might be the source of the problem?

An example of how difficult IM can be to find:

Two years ago we received a report of interference from our repeater
(on 147 MHz) to one of the services in Lansing. (that's about 70
miles). The interference was intermittent.

It turned out that there were three stations involved and none were
within 30 miles of each other.

Out repeater signal and a pager in (I believe it was Chesasining MI)
was mixing in a commercial repeater (fire I believe) and being
retransmitted on the input frequency for a Police repeater in Lansing.
The resultant signal being well off the frequencies used in the other
repeaters was understandably weak, but strong enough to key the Police
repeater and be clearly understandable.

It took several weeks of dedicated hunting by a number of crews in an
area nearly a 100 miles by about 30 miles to finally locate the
offender.

snip

At this point the question is whether the interference poses a threat to
safety or merely an annoyance. When the interference "breaks squelch while
you are tuned to the TRACON freq are you still able to hear the controller
when he/she transmits?

On one installed radio and the handheld, yes. On the other installed
radio, the controller becomes very faint against a background of
continued noise.

IF the signal bothers one receiver far more than the other then I
would think the problem is more likely on the plane. IF it is
external and close, both receivers on the same frequency should have
the same problem.

To me that says "bad connection" some where.

There are many other possibilities, but with that information I'd tend
to lean heavily toward "on board"

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

It may be a good idea for you to notify the FAA about the problem.

OK, I was thinking about this. Can you suggest which person in the
FSDO I'd ask for?

Thanks,
Sydney