I did a three part series in Kitplanes a couple of years ago on how to
homebrew your own audio panel for situations exactly like this.

BE AWARE OF A GLITCH IN THE MICROAIR radio that requires the key line to be
within 0.5 volts of ground in the "keyed" mode. Don't go doing any diode
switching with your audio panel design or the sucker won't key correctly.
Standard aircraft specification, by the way, is 3 volts or less is keyed,
more than 3 volts is unkeyed.

Jim



wrote in message
ups.com...
I have a panel mount Microair transceiver and Xcom Intercom in my
homebuilt. I also take along a Vertex handheld transceiver when I fly.
Does anyone know of a small, (space is very limited), audio panel that
would
allow me to switch between the Microair and handheld?