KT-76 low power?

Hey all... finally got around to taking a trip in my plane this
weekend (busy with school stuff). The transponder appears to be weak and
the controllers were none-too-pleased without seeing a squawk, IFR,
running next to a TFR... They had a tough time receiving my squawk,
especially when far out. I saw the blinky-blinky interrogate light
lighting up just as normal, though. I just (June) took it in for IFR cert
and they said it was all fine.

I thought it might be disconnected antenna or dirt on it, but the
BNC connector looks new and antenna was slick and clean. I'm assuming
this thing is old enough to have a tube output that might be losing power?
I think I will first try replacing the antenna and entire coax run... it's
cheap and easy to do.... just looking for other thoughts.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Is it a KT76 or a KT76A? I just took my KT76 in because it "received" but
did not transmit.
They put it on the bench and 260watts output but at the wrong freq(just
adjustment). I believe the
KT76A is more reliable than the KT76 for stability. Anyway, $175 later it's
in the plane
but not tested yet. It needed some service bulletins performed also....
John

wrote in message
...
Hey all... finally got around to taking a trip in my plane this
weekend (busy with school stuff). The transponder appears to be weak and
the controllers were none-too-pleased without seeing a squawk, IFR,
running next to a TFR... They had a tough time receiving my squawk,
especially when far out. I saw the blinky-blinky interrogate light
lighting up just as normal, though. I just (June) took it in for IFR cert
and they said it was all fine.

I thought it might be disconnected antenna or dirt on it, but the
BNC connector looks new and antenna was slick and clean. I'm assuming
this thing is old enough to have a tube output that might be losing power?
I think I will first try replacing the antenna and entire coax run... it's
cheap and easy to do.... just looking for other thoughts.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

John P wrote:
: Is it a KT76 or a KT76A? I just took my KT76 in because it "received" but
: did not transmit.
: They put it on the bench and 260watts output but at the wrong freq(just
: adjustment). I believe the
: KT76A is more reliable than the KT76 for stability. Anyway, $175 later it's
: in the plane
: but not tested yet. It needed some service bulletins performed also....
: John

It's a 76, not a 76A. I just took it up the other day after getting back, and
the local Class-C was able to see me from 2000' AGL, 20 miles away in "mountainous"
(i.e. Appalachian) terrain. Whatever it is, it's either low power, intermittent
problem, or both. I suppose it could be a frequency tolerance issue and some
centers/approaches are more tolerant of that. Wouldn't an transponder cert check
that?

-Cory


--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote:
It's a 76, not a 76A. I just took it up the other day after getting back, and
the local Class-C was able to see me from 2000' AGL, 20 miles away in "mountainous"
(i.e. Appalachian) terrain. Whatever it is, it's either low power, intermittent
problem, or both. I suppose it could be a frequency tolerance issue and some
centers/approaches are more tolerant of that. Wouldn't an transponder cert check
that?

Cory,

Transponder reception problems are usually caused by being off-frequency
or a/c gate misalignment. The older units really do drift over
time...hence the importance of the 2 year check. A simple test at your
avionics shop can reveal what's wrong, and chances are it just needs an
adjustment.

That said, if the problem is ultimately determined to be the tube or
some other hard-to-diagnose intermittent problem, I have a KT76 in good
operating condition that I could let you have for a steal. Email me if
you are interested.

-Doug

--
--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

Speaking of KT-76A's, the little 'blinky' interrogation light on the
front of mine gave up the other day. The transponder still reports
just fine as confirmed by San Antonio class-C controllers. But no
indication light.

Anybody know how difficult it is to replace the light (bulb) or what
type it is???


Chuck



On Thu, 16 Sep 2004 12:34:22 GMT, Doug Vetter
wrote:

wrote:
It's a 76, not a 76A. I just took it up the other day after getting back, and
the local Class-C was able to see me from 2000' AGL, 20 miles away in "mountainous"
(i.e. Appalachian) terrain. Whatever it is, it's either low power, intermittent
problem, or both. I suppose it could be a frequency tolerance issue and some
centers/approaches are more tolerant of that. Wouldn't an transponder cert check
that?

Cory,

Transponder reception problems are usually caused by being off-frequency
or a/c gate misalignment. The older units really do drift over
time...hence the importance of the 2 year check. A simple test at your
avionics shop can reveal what's wrong, and chances are it just needs an
adjustment.

That said, if the problem is ultimately determined to be the tube or
some other hard-to-diagnose intermittent problem, I have a KT76 in good
operating condition that I could let you have for a steal. Email me if
you are interested.

-Doug

NoOne wrote:

Speaking of KT-76A's, the little 'blinky' interrogation light on the
front of mine gave up the other day. The transponder still reports
just fine as confirmed by San Antonio class-C controllers. But no
indication light.

Anybody know how difficult it is to replace the light (bulb) or what
type it is???

I dunno, but it also has a photosensor that controls the lights
intensity. So it could be more than simply just the bulb...

Hrm... certainly could be it, but I would think that the IFR transponder cert
(just done in June!) would have discovered that. Things won't drift *that* fast.

It really bugs me that I don't have the equipment to test transponder/dme
stuff. Most other equipment I've been able to troubleshoot with other "easily
generatable" test signals, those I need to fly the plane. Trouble with taking it "to
my avionics shop" is that there isn't one around here. I guess a valid question would
be whether or not an old transponder like this would keep kicking for awhile if given
some $$$ for a tuneup.

-Cory

Doug Vetter wrote:
: wrote:
: It's a 76, not a 76A. I just took it up the other day after getting back, and
: the local Class-C was able to see me from 2000' AGL, 20 miles away in "mountainous"
: (i.e. Appalachian) terrain. Whatever it is, it's either low power, intermittent
: problem, or both. I suppose it could be a frequency tolerance issue and some
: centers/approaches are more tolerant of that. Wouldn't an transponder cert check
: that?

: Cory,

: Transponder reception problems are usually caused by being off-frequency
: or a/c gate misalignment. The older units really do drift over
: time...hence the importance of the 2 year check. A simple test at your
: avionics shop can reveal what's wrong, and chances are it just needs an
: adjustment.

: That said, if the problem is ultimately determined to be the tube or
: some other hard-to-diagnose intermittent problem, I have a KT76 in good
: operating condition that I could let you have for a steal. Email me if
: you are interested.

: -Doug

: --
: --------------------
: Doug Vetter, CFIMEIA
:
: http://www.dvcfi.com
: --------------------

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Doug Vetter wrote:
: Transponder reception problems are usually caused by being off-frequency
: or a/c gate misalignment. The older units really do drift over
: time...hence the importance of the 2 year check. A simple test at your
: avionics shop can reveal what's wrong, and chances are it just needs an
: adjustment.

Oh, I forgot to mention that might be applicable for someone who knows more
about adjusting these things. You mentioned a/c gate misalignment and that jogged my
memory on this thing. The "reply" light has always been a bit flaky on this box.
When it's receiving a signal, it's always done a quick, multiple flash... pretty much
at every interrogation. It doesn't just pulse once every few seconds like it
should... always blink-blink-blink-pause-blink-blink-blink-blink-pause....

Certainly sounds like it could be some digital timing gone awry and it's just
"marginally worked" before.

What say you (all)?

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************