"Seagram" writes:

Portable PTTs come in two flavors: the kind that pass audio through all the
time, and the kind that only pass audio through when the radio key is
pushed. You need the kind where the audio can get through all the time.

It's easy to convert one that doesn't always pass the audio though. It's
just a matter of bridging one side of the switch. I hacked my old DC
switch and it's worked well for years.

(I had a flight instructor swear up and down that it couldn't be done.
I hated flying with him. That didn't last.)

--kyler