Jay Honeck wrote:

Hey Mike,

What's the cure for "bleed through" from one com radio to the other?

Usually "bleed through" refers to the effects of RF overload on Com2
while transmitting on Com1, or vice versa. Most audio panels contain
automatic muting circuits which completely block the audio from opposite
com reciever while the other's transmitter is keyed.

We usually keep "Com 2" tuned to our local AWOS frequency. When we're near
Iowa City, we can faintly hear it in the background through our
headphones -- even when "Com 2" or "Both" aren't selected on our audio
panel.

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.

It is likely that your installer did something funky with the audio
wiring between Com1/Com2 and the audio panel to induce this. Could be
that the Speaker outputs of the Com radios are wired to 8 Ohm dummy load
resistors inside the audio panel. If the installer took a shortcut and
shared the ground connection from speaker-low output on the Com(s) to
the audio ground on the audio panel, it created a classic ground loop
between the speaker audio loop and the headphone output loop, thereby
creating the crosstalk. Better wiring technique might have prevented this.

Most modern Com radios dont care if the speaker outputs are terminated
into a dummy load resistor when not connected to the overhead speaker,
so it isn't even necessary to utilize those loads built into the audio
panel.

Of course, this isn't an issue without ANR headsets (couldn't hear it), or
when we're far enough away from the strong signal -- but it's one of those
little annoyances that always bugs us.

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.
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.

MikeM
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