where exactly to put the noise filter

Jay Honeck wrote:

This sounds like inadequate isolation in the audio source switching of
the audio panel. Most of modern audio panels (King, PSE, RST) do not
intrisically have this problem. I think you have a PSE, which shouldn't
do this.


Actually, I have a Narco CP-136 audio panel.

I do not have any experience with these, so the lack of isolation could be
a shortcoming of the design.

(See a picture of this model at http://www.ronhahn.com/Hawk-XP/CP136.html )


For further diagnosis, I'll bet that if you turn the volume control of
the non-selected comm radio down, then the bleedthrough will go away.


Yep, I believe it does. So this means the audio panel is wired incorrectly?

It just means that the bleed-through is happening at audio frequencies; not by
one IF coupling to the other IF as another poster postulated.


Also try switching the non-selected com receiver to the overhead speaker
while listening to the primary com on the ANR headsets, and report back.


Okay, will do. I should expect to hear the AWOS broadcasting quietly on the
speaker, I presume, same as I hear in my headset?

Yes, but try to determine if the faint feedthrough you hear in your headphones
is reduced by routing com2 to the speaker. It will be a subtle difference,
because the speaker audio will leak into your headphones accoustically. If the
feedthrough is reduced, then my speculation about the dummy load resistors would
warrant more investigation.

MikeM
Skylane '1MM
Pacer '00Z