On Feb 21, 7:04*pm, Darryl Ramm wrote:

The ball being plastic is a bit strange. I'd find an all
metal one next time.

Yup, I was surprised too but this seems to be Piper original equipment
fit and the TED antenna, which is now obsolete, was mostly fabricated
by TED but has a ball end and mounting disk (washer) supplied by King
(now Honeywell). The current model TED antenna has a brass ball end
but it does not fit the hole in the aircraft. I chased down the
drawings so I could buy a brass ball and drill and tap it to fit the
antenna. That would have detuned it and probably made my problem
worse.

I had a private email from an MRX user who had experienced a similar
spurious threat problem. In his case it was caused by a
malfunctioning MRX baro sensor. I can see that if the sensor
originally tracked the local transponder alt and then stepped off and
drifted back it could cause the symptoms I see.

Part of the difficulty is that I have been chasing multiple problems.
The really critical one was that my encoder was thousands of feet in
error when cold. That was fixed a while a go by buying a new one but
proving it was the problem required making an encoder test box and
running some cold soak tests. (I reported on that earlier).

ZAON customer sircice has been helpful and suggested I send it back
for testing but, being a stuborn engineer, I want to characterize the
problem first

Andy