Transponders and ATC's Radar

Marco Leon wrote:
Has anyone out there experienced transponder problems with one controller
but not with a subsequent controller after a hand-of?

For the third time yesterday (with the other two occurring over the past
year or so) a NY Approach controller informed us that our transponder was
only responding with a squawk and altitude once every couple of minutes or
so. However, upon hand-off to another controller (who I believe was in the
same facility), it was rock-solid. This has happened a couple of times
before--all with NY Approach--where one guy said our xponder was inop and
the next guy said it was fine. I don't think it was a warm-up issue since
the last time it was on the descent from a long flight.

Any ideas? I don't want to send-off my transponder for service unless I'm
reasonably sure that the problem could be with the box.


If it's an old KT-76/KT-78 it may be slightly off-frequency.
Other makes of similar design age are also suspectible.

One SSR (also called an interrogator) may have a wider tolerance
to incoming response frequency than another. Of course, this line of
thought needs that the controllers are looking at different
SSR sensor stations.

The frequency adjustment is simple. The transponder usually
starts to drift off-frequency when the transmitter tube
(valve in British) gets old.

HTH

--

Tauno Voipio
tauno voipio (at) iki fi

That sounds about like what my avionics shop said. I clearly remember
them saying something about the transponder being slightly out of phase.

I have heard about problems where the transponder appeared inop at one
class D, but was good at the next a few miles away. Apparently the
transponder's frequency was slightly off and some ground equipment
could read it, while the other ignored it.
That there should be an issue simply because a different controller has
you on his screen sounds odd.
As others have suggested recalibrating your transponder (or replacing
worn out tubes) should make sure that it operates on exactly the right
frequency.