Garbled transmission from my '66 172G

Garbled transmission from my '66 172G

Was wondering if anyone could help steer me to a solution:
Aircraft has new Flightcom 403MC voice activated intercom, Terra TMA230D audio panel, com 1 is an ARC, com 2 is Narco MK12D. While inbound on a flight about 1 week ago, tower advised me that my transmission was garbled & they could barely understand me, but cleared me for the approach.  As we neared closer, tower said they could understand a little better.  We made our approach, and landed.  A neighbor pilot who keeps his airplane at a hangar just across from mine happened to be 3-4 miles behind us on approach, and stated that he could understand us clearly throughout the approach.  Testing led me to question the PTT switch in my airplane, which was replaced.  While ground testing to validate the switch replacement, tower once again confirmed garbled transmission.  I borrowed my neighbor’s H10-30 David Clark headset, which is more well-used than mine, and tower was able to clearly hear all ground radio transmissions.
What I do not understand: Each of my David Clark H10-13.4 headsets sounded fine to us while using the airplane intercom --- no choppy cutoff’s & absolutely no indication of any “garbled” communications, while at the same time tower confirmed “garbled”.  Is there any way, any chance that both of my David Clark headsets could be experiencing a similar problem at the same time?  It seems like switching to someone else’s headset “clears” my airplane from further investigation.  Are there any suggestions?

cppiechowiak
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Re: Garbled transmission from my '66 172G

It could be that your headset mics are louder than the one you borrowed.  The intercom may handle it ok, but the radios may be over modulating a bit.  If I remember correctly, there may be a trimmer pot of the headset mics that allow you to adjust the mic volume. Also, be sure to use a mic sock.... it cuts down the ambient noise!

Hope that helps!

Bob

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Re: Garbled transmission from my '66 172G

Bob, thanks for the response.  I will look into the trimmer pot idea.  So far I did find one loose microphone connection on one of my headsets, and a microphone jack that had a shoulder washer that had insufficient shoulder to prevent the microphone jack from occassionally contacting ground (on the Flightcomm intercom that I have, all microphone jacks must not be at ground potential & need to be isolated from the mounting brackets).  Seems to be working better now.

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