Transponders and ATC's Radar

[Marco Leon]

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.

Marco



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[Robert M. Gary]

Yes, I've had this happen. I don't understand all the physics behind it
but the transponder replies after a set amount of time. Apparently, if
that time is off a variety of variables could cause certain controllers
to have problems (perhaps distance from transmit station). In any case,
an hour in the avionics shop fixed the problem for good.

-Robert

[Marco Leon]

What did the shop do? Adjusted settings? Replaced tubes? Both?

"Robert M. Gary" > wrote in message
oups.com...
> Yes, I've had this happen. I don't understand all the physics behind it
> but the transponder replies after a set amount of time. Apparently, if
> that time is off a variety of variables could cause certain controllers
> to have problems (perhaps distance from transmit station). In any case,
> an hour in the avionics shop fixed the problem for good.
>
> -Robert
>



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[Robert M. Gary]

They just did some sort of adjustment. It wasn't expensive.

[Denny]

Likely they did nuttin other than a normal check out for actual
failure... The problem is often with TRACON receivers not the
transponder... In my locality there is an area about five miles across
where many aircraft are told they need to reset their transponder...
Having flown this area for decades, when told that by the controller
while near this area I simply reply, "roger that 5 7 pop", and do
nothing... Sure enough 3 or 4 miles later he informs me "Mode C
received"... I reply, "roger that 5 7 pop"...


denny

[Tauno Voipio]

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

[Robert M. Gary]

> Likely they did nuttin other than a normal check out for actual failure...
No, they found something "out of phase". Since then I"ve not had a
problem. If the radio is out of phase some ATC's will have problems,
others will not. Best solution is to fix the radio.

[Robert M. Gary]

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

[[email protected]]

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.

[Marco Leon]

"Denny" > wrote in message
oups.com...
> Likely they did nuttin other than a normal check out for actual
> failure... The problem is often with TRACON receivers not the
> transponder... In my locality there is an area about five miles across
> where many aircraft are told they need to reset their transponder...
> Having flown this area for decades, when told that by the controller
> while near this area I simply reply, "roger that 5 7 pop", and do
> nothing... Sure enough 3 or 4 miles later he informs me "Mode C
> received"... I reply, "roger that 5 7 pop"...

Now THAT's interesting. I have a suspicion that that may be the case.
However, Gary's experience as well as other's I've seen on Goggle searches
point to at least a partial blame on the box. Maybe certain radars won't see
weak signals?

Marco



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[Private]

"Marco Leon" <mmleon(at)yahoo.com> wrote in message
...
> Has anyone out there experienced transponder problems with one controller
> but not with a subsequent controller after a hand-of?
>
snip

I seem to remember reading reports of the transponder antenna from a Diamond
Katana being shielded by the front landing gear leg.

Happy landings,