How can I add a back seat intercom?

[Mike Gilbert]

I often rent Cessna 172's that come pre-equipped with headset jacks for radio
and intercom for both front-seat passengers (including separate push-to-talk
buttons for the radio.)

However, there are no headset jacks in the back seat, so the pilot/co-pilot
can't chat with any back seat passenger(s) during cross-country trips.

What can I buy to use in rental planes to add intercom capability to the back
seat? I've seen headphone/microphone splitter cables on sale from Sporty's,
and there are various portable intercom units. But are the splitter cables
what I want? Can the portable intercom units piggyback on a built-in intercom
system? Or are there other solutions that I'm overlooking?

Thanks,

Mike Gilbert
uunet!sli!jng j...@sli.com

[Geoff Peck]

In article <1991May16.1...@sli.com> j...@sli.com (Mike Gilbert) writes:
> What can I buy to use in rental planes [which are equipped with two-place
> intercoms] to add intercom capability to the back seat?

You can give the back seat folks "listen-only" capability by using splitter
cables. I wouldn't recommend this for the microphones, though.

The simplest solution is to turn off the intercom in the airplane and plug
your own four-place portable intercom into the airplane at the pilot
station. Turning off the built-in intercom should result in having the
pilot's mic and headset jacks connect directly to the radios ("fail-safe"
operation).

Piggybacking a portable intercom with the built-in may not work -- the
microphone output from the portable may or may not drive the built-in, and
there may be funny interactions between the two squelch circuits.

Geoff