Can not monitor both com radios

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I need help on my RV-8. I have installed an FlightCom 403LSA intercom and two com radios, a Becker and flightcom. I am using switches (not an audio panel) to change which com radio to transmit on and monitor.

When I have one monitor switch off, the other radio works as expected. So if I transmit on com 1 and only monitor com 1, everything is great. Same with com 2.

The problem occurs when I have both monitor switches on, and can monitor both com radios. The signal from com 2 (the flightcom) is decreased. If I turn the radio volume way up, I can hear it, but this is not right. Do you have some suggestions as to what I can do to make the volume on both radios the same when monitoring both radios. I'm thinking I need a diode on the headphone lines so the signal from the radios do not go into the other radio.

Thanks for any help
N808JA

 

[BobTurner]

You’re on the right track: when the audio signals ‘look’ backwards, into the other receivers’ output, they see nearly a short circuit. The easy fix is to install two resistors, each around 330-480 ohms, in series with each audio output coming out of each radio. The volumes may still need a minor adjustment going from one radio to both, but it will work.
The proper fix is to build an audio ‘mixer’ circuit. Some soldering needed, about $1 worth of electronics.
I’d build the mixer if you have three or more signals to mix; the resistors work okay for just two.