wrote in message ...
I would start by disconnecting the antennas from ALL of the receivers
or if the antenna does not have a separate connector then removing the
receivers and using the hand held to detect the offending signal. If
you inject a strong enough signal into the antenna input you force the
receiver's RF amp into overload and it generates the intermod products
and sends them back OUT the same antenna to be picked up by the other
antenna's

OK, here is what I don't understand:

We have this problem with the airplane's master switch turned OFF

Can the receiver's RF amp generate intermod products when the
power is switched OFF?

We have some avionics which don't have separate off switches
(the KMA20 audio panel/mb is one) but the only thing which
operates independently of the master switch is the airplane's
clock.

If the antenna farm itself is generating intermod products,
can it be picked up by an installed antenna (connected to a
receiver which is turned OFF) and re-radiated to our comm
antennae?

There is one brand of ELT that is infamous for this type of problem
but I can not remember the model and brand.

This was suggested to us initially. We disconnected the ELT
(but DH left it sitting in the back seat of the plane unfortunately,
instead of on the ground) and we still had the problem.

So people at the time thought that pretty much absolved the ELT
(it's an old one-Narco 10). I could certainly disconnect and
physically remove the ELT and see if that helps.

It's not that I'm unwilling to disconnect all the antennae in the
plane, but some of them are a terrible PITA to reconnect and I'd
like to understand the theory of what's supposed to be happening
to produce this problem with the power to all of the receivers
turned OFF.

Thanks,
Sydney