[amsat-bb] Intermittent loss of full-duplex with Arrow, built-in-duplexer and TH-D72a

John Brier johnbrier at gmail.com
Fri Aug 19 17:48:01 UTC 2016

For the third time I've lost the ability to hear myself on the
downlink of SO-50 using this setup. This was on today's 1521 UTC SO-50

In the past I had what appeared to be very similar behavior with a
different arrow antenna, no duplexer and two radios. I troubleshot
that issue to the screw in the gamma match coming lose which caused
high SWR.

In this case I tested the SWR with my MFJ-259B SWR analyzer and it was
1.1:1 and X=45-55 across almost the entire band.

I actually was able to hear myself in the beginning of the pass and
then it got worse until the point where I could not hear myself for
the rest of the pass.

Actually, in this case, unlike the other two times where I wasn't able
to hear myself on the downlink I had another unusual behavior which
was I *WAS* able to hear myself but it was extremely loud and
distorted. This happened maybe twice in the middle of the pass and
then after that I just couldn't hear myself when I transmitted.

When I was able to hear myself very loud and distorted I felt it
wasn't how I was getting into the bird, but somehow my radio was
demodulating my 2 meter transmission. I confirmed with W4FS who was
also on this pass that my audio never sounded odd.

Very annoying and my only guess as to what could be causing this is
some sort of external interference occasionally getting into my radio.

Any ideas?

73, John Brier KG4AKV

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