A couple of months ago I flew down to my father's farm to survey some
recent storm damage, and while orbiting the place to take pictures, I
heard the local Army ATC warn a helicopter about my position. The
helicopter said he didn't have me in sight, and ATC replied that I had
my transponder "turned off". This was pretty alarming news, and when I
got near home I requested HSV approach to verify they had my position,
and they couldn't located me, even with IDENT! I subsequently requested
a PAPR ADSB performance report (as I usually do after each flight), and
discovered that "baro alt" was 100.0% failure! The previous flight had
a high percentage of baro alt failure, but was usually 100% pass on
previous flights.
So this was quite sudden, and I couldn't imagine why, but I went through
the echoUAT setup and verified everything was correct, as well as
checked out the wiring and mounting, making sure nothing was
disconnected or shorting the antenna. I even swapped the antenna with a
known good one and went for another flight....same 100% failure rate. I
also checked the antenna cable, using an ohm meter to check for
continuity and shorts, and it was fine. I couldn't swap the cable out
to check it because of the weird combination of connectors on each end,
nor did I have a proper tester for it anyway.
The Becker transponder appeared to be working properly, complete with
displaying my baro altitude in the display just like it always did. But
I got no interrogation indication, so assumed something was wrong with
the transponder....so I sent it out for repair. They ran it all day
long on their test equipment, and said it was fine, suggesting I check
my antenna or antenna cable. I found this hard to believe, as this
antenna cable was professionally made, and was only a few years old, but
I ordered another one (and custom cables with different connectors on
each end are not cheap)! After replacing the cable all subsequent
flights have been 100.00% pass!
I'm not sure of the moral of this story, but don't rule out all
possibilities when troubleshooting this kind of stuff. I'm also quite
impressed with this Becker transponder, as it's worked flawlessly for 15
years now. The previous transponder, a Terra, croaked early because the
antenna connector worked itself loose, and apparently fried the output
stage due to a lack of "load". Something else to worry about....
--
Mark Langford
m...@n56ml.com
http://www.n56ml.com
Huntsville, AL
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