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Here's something you might look into re: strange noises when transmitting.

I, as I'm sure has everyone else, have two sets of headset/mike plugs
installed in my airplane. Both headsets are almost always left plugged in,
even when no one is in the right seat.

Never had too much of a problem with any kind of radio noise until one day,
for some unknown reason, I removed the passenger headset and went flying (or
started to). The first time I keyed the mike to ground control, I was
inundated with the most horrible racket I'd ever heard! I thought my radios
had gone belly-up for sure. It was so bad, I turned around and taxied back
to the hangar and shut down, ready to find out what terrible thing had
happened to the electrical system since the last time I had flown. While I
sat there, I tried to think what I had done - believe me - something as
innocuous as un-plugging a headset just didn't register for quite a while.

Anyway, long story short, and all of that, when I finally got around to
plugging it back in, PRESTO! all was as it had been before. Theorizing, I'm
guessing that with the headset out of the loop, the phone and mike wires are
un-terminated (both the phones and mike are a fairly low impedance short on
those wires when connected) and are acting like great big antennas running
straight back into the radios. Since my headset plugs are mounted behind the
seat, it means that those wires are fairly long and, running back through
the center console, are in close proximity to the com antenna cables. I was
surely getting a powerful feed-back that was driving the radio circuits (and
the controllers) crazy!

Can't guess that this is what might be happening to those of you having
problems since every Lancair is probably unique in it's wiring
characteristics, but it wouldn't hurt to check it out.

Hope it helps.

Dan Schaefer

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