"scratchy" radio transmission

Jim, do you have an audio mix panel, and if so does the mic input go
to it before splitting to the radios? Also, I read your original post
pretty quickly and didn't notice the part where you said you were
hearing the sidetone okay. That eliminates a lot of potential failure
points.


Another thought: Do you have an "intercom" that both mics and the PTTs

connect to before the mic audio gets to the radios? If so, the
intercom
could be the culprit. There are so many ways that your aircraft could
be wired up that its hard for me to think of all of them. You could
probably get to the bottom of it all pretty quickly with an
oscilloscope
if you have one and know how to use it.


RST, if both radios have the same static problem (with their different
RF XMIT sections, T/R switches, and antennas), it is not very likely an

RF problem.


OTOH, it could be a DC voltage problem, as in the DC voltage supply to
the radios is too low, causing the transmit power to be less than it
should.


Jim, have you tried both radios and verified that ATC hears them both
as
scratchy?

No audio mix panel. Mic goes to the intercom then goes through a DPTT
switch (to deliver Mic to either radio but not both at the same time
and same with the PTT and audio output). When the intercom is turned
off the mic input bypasses it straight to the radios and it is the
'radio' sidetone I hear clearly from both radios, not the intercom's.
ATC verifies both radios sound the same. I used to suspect the landing
gear getting in the way but as I said I have one antenna on the bottom
and another on top. Since I'm always headed to the facility on callup I
even had the whacky idea that the metal prop was getting in the way so
I would turn the plane 90 degrees and call again. Needless to say, no
difference.
I am also leaning to checking the DC supply circuits again. Thanks.

Jim