Transponder replacement suggestions

[[email protected]]

Hey all... just got official confirmation that my KT76's power output is way
low.... classic sign of weak/dying/dead cavity tube. Just looking for suggestions on
what might be a good, cost-effective replacement. I'm tired of futzing with
transponders so I'm pretty sure I want a solid-state replacement.

I just had a thought too (for any avionics techs reading)... perhaps the lack
of DME suppression lead to the premature demise of the KT76? I was going to wire it
up when I installed the DME, but the KT76 doesn't have that capability. Maybe the DME
cooked it?

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Dan Luke]

> wrote:

> Hey all... just got official confirmation that my KT76's power output is
> way
> low.... classic sign of weak/dying/dead cavity tube. Just looking for
> suggestions on
> what might be a good, cost-effective replacement. I'm tired of futzing
> with
> transponders so I'm pretty sure I want a solid-state replacement.

Garmin's 327 is awesome. I bought one 4 years ago; no xponder worries
since.

--
Dan
C172RG at BFM

[Nathan Young]

On Wed, 10 May 2006 11:59:58 +0000 (UTC),
wrote:

> Hey all... just got official confirmation that my KT76's power output is way
>low.... classic sign of weak/dying/dead cavity tube. Just looking for suggestions on
>what might be a good, cost-effective replacement. I'm tired of futzing with
>transponders so I'm pretty sure I want a solid-state replacement.
>
> I just had a thought too (for any avionics techs reading)... perhaps the lack
>of DME suppression lead to the premature demise of the KT76? I was going to wire it
>up when I installed the DME, but the KT76 doesn't have that capability. Maybe the DME
>cooked it?

I would get another KT76. As with all avionics, install price
dominates the end cost.

Alternatively, are there any pin-compatible transponders (for KT76)?

[[email protected]]

Nathan Young > wrote:
: > I just had a thought too (for any avionics techs reading)... perhaps the lack
: >of DME suppression lead to the premature demise of the KT76? I was going to wire it
: >up when I installed the DME, but the KT76 doesn't have that capability. Maybe the DME
: >cooked it?

: I would get another KT76. As with all avionics, install price
: dominates the end cost.

... except in my case.... :) Re-working the transponder tray is something I
can do in an afternoon and my mechanic is perfectly happy to sign it off.

: Alternatively, are there any pin-compatible transponders (for KT76)?

... but yes there are a few pin-compatible ones now that I've looked a bit.
It looks like the Narco AT165 comes in a couple of different flavors including a
replacement for KT-76, KT-76A, AT-150, or ARC. The garmin low-end ones (GTX320?) also
can come in different flavors.

Another thing I thought of as I wrote the original post was the DME
suppression. It's a wire that disables the receiver on the transponder when the DME
transmits its pulse. It prevents interference with the transponder, and allegedly can
damage the transponder. The KT76 unit does not have this capability, nor does the
connector even have and extra space for it. SO, if I get a new one that's
tray-compatible, I cannot wire that up, which isn't good.

-Cory


--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Thomas Borchert]

Garmin 330 if you want/need Mode S, otherwise the 327 is great.

--
Thomas Borchert (EDDH)

[Peter R.]

> wrote:

> Hey all... just got official confirmation that my KT76's power output is way
> low.... classic sign of weak/dying/dead cavity tube. Just looking for suggestions on
> what might be a good, cost-effective replacement. I'm tired of futzing with
> transponders so I'm pretty sure I want a solid-state replacement.

Hey, Cory - Just an FYI as I am NOT a salesman, but I have a perfectly
working KT76A that I pulled out of my Bonanza when I installed a Garmin
GTX330.

I had been meaning to put it on eBay, but procrastination sank in and six
months later, I still haven't done so. If you are interested in it, drop
me a note at pjricc @ gmailX.com (remove the x) and I can send you any
information you might need.



--
Peter

[Frank Stutzman]

Thomas Borchert > wrote:
> Garmin 330 if you want/need Mode S, otherwise the 327 is great.

Didn't I hear that TIS (traffic information service, or something like
that) is not going to be developed any further? If thats the case, what
is the value (to the pilot) of Mode S to your average part 91 flyer?

--
Frank Stutzman
Bonanza N494B "Hula Girl"
Hood River, OR

[Thomas Borchert]

Frank,

> Didn't I hear that TIS (traffic information service, or something like
> that) is not going to be developed any further? If thats the case, what
> is the value (to the pilot) of Mode S to your average part 91 flyer?
>

Correct. Here in Europe, Mode S transponders are (becoming) mandatory,
however.

--
Thomas Borchert (EDDH)

[Peter R.]

Frank Stutzman > wrote:

> Didn't I hear that TIS (traffic information service, or something like
> that) is not going to be developed any further? If thats the case, what
> is the value (to the pilot) of Mode S to your average part 91 flyer?

As an owner of a Garmin GTX 330 with traffic displayed on my MX20, I would
suggest that there is still value in a mode S transponder with TIS, if the
pilot flies a lot in the busy northeast, southeast (Florida), and/or
southwest.

While it is true that the FAA is actually disabling TIS for those radar
sites that they are upgrading, my understanding (based on reading articles
in _IFR_ and _Aviation Consumer_) is that this upgrade is happing slowly,
sometime over the next four to five years, and that the number of sites
that will eventually have TIS disabled is a relatively small number when
compared to the total number of sites that provide TIS.

_Aviation Consumer's_ last article on the subject still advocated TIS as a
cost effective, in-cockpit traffic awareness tool for the next few years.
Of course, if the FAA does get their act together with regards to the
nationwide deployment of ADS-B then this recommendation would change, but
the editors of AC still believe ADS-B is five or more years away from
nationwide deployment.

--
Peter

[Ray Andraka]

Nathan Young wrote:

> On Wed, 10 May 2006 11:59:58 +0000 (UTC),
> wrote:
>
>
>> Hey all... just got official confirmation that my KT76's power output is way
>>low.... classic sign of weak/dying/dead cavity tube. Just looking for suggestions on
>>what might be a good, cost-effective replacement. I'm tired of futzing with
>>transponders so I'm pretty sure I want a solid-state replacement.
>>
>> I just had a thought too (for any avionics techs reading)... perhaps the lack
>>of DME suppression lead to the premature demise of the KT76? I was going to wire it
>>up when I installed the DME, but the KT76 doesn't have that capability. Maybe the DME
>>cooked it?
>
>
> I would get another KT76. As with all avionics, install price
> dominates the end cost.
>
> Alternatively, are there any pin-compatible transponders (for KT76)?
>
>

Yes, Narco has a slide in replacement based on their AT165. I've got an
AT165 in my airplane and am very happy with it.

[Newps]

Frank Stutzman wrote:
> Thomas Borchert > wrote:
>
>>Garmin 330 if you want/need Mode S, otherwise the 327 is great.
>
>
> Didn't I hear that TIS (traffic information service, or something like
> that) is not going to be developed any further? If thats the case, what
> is the value (to the pilot) of Mode S to your average part 91 flyer?

Mode S will be required in the not too distant future as ADS-B gets
rolled out.

[Bob Noel]

In article >,
Newps > wrote:

> > Didn't I hear that TIS (traffic information service, or something like
> > that) is not going to be developed any further? If thats the case, what
> > is the value (to the pilot) of Mode S to your average part 91 flyer?
>
> Mode S will be required in the not too distant future as ADS-B gets
> rolled out.

I doubt it. Seriously. There really isn't a case for Mode S. It's been a
solution in search of a problem for years and years and years.

--
Bob Noel
Looking for a sig the
lawyers will hate

[Jay Honeck]

> Garmin's 327 is awesome. I bought one 4 years ago; no xponder worries
> since.

I'll "second" Dan's endorsement of the GTX-327. I replaced an old
Narco transponder with the 327 several years ago, and we absolutely
love it.

Just check out how many new aircraft come with it as standard
equipment, and you'll see that Dan and I aren't alone in our
assessment.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[skym]

I'll admit to some lack of knowledge here but, other than the Mode S
ability of the Garmin 330, aren't xpdrs pretty much just a one trick
pony? I.e., they just receive a radar signal and reply. Why would a
Garmin 327 be any better than any other?

[Matt Barrow]

"skym" > wrote in message
ups.com...
> I'll admit to some lack of knowledge here but, other than the Mode S
> ability of the Garmin 330, aren't xpdrs pretty much just a one trick
> pony? I.e., they just receive a radar signal and reply. Why would a
> Garmin 327 be any better than any other?
>
No cavity tube for one. Push button entry, VFR button, solid state
electronics...

[skym]

Good points, but do they even make them with cavity tubes or without
solid state electronics anymore? Also, at what price to push "VFR" vs
push/dial in 1200?

[Matt Barrow]

"skym" > wrote in message
ups.com...
> Good points, but do they even make them with cavity tubes or without
> solid state electronics anymore?

Don't know...but that's a point when considering it as a replacement BEFORE
the old unit fails.

> Also, at what price to push "VFR" vs
> push/dial in 1200?

By itself, nothing.

It's ironic, though, how such a simple, cheap to implement feature gets left
out on other products.

[Newps]

skym wrote:

> Good points, but do they even make them with cavity tubes or without
> solid state electronics anymore?


Yes, they still make them with cavity tubes

[Ray Andraka]

Matt Barrow wrote:
> "skym" > wrote in message
> ups.com...
>
>>I'll admit to some lack of knowledge here but, other than the Mode S
>>ability of the Garmin 330, aren't xpdrs pretty much just a one trick
>>pony? I.e., they just receive a radar signal and reply. Why would a
>>Garmin 327 be any better than any other?
>>
>
> No cavity tube for one. Push button entry, VFR button, solid state
> electronics...
>
>

Narco AT155 and AT165 are also solid state and have the push to squawk
VFR feature, as well as some timers. IIRC, the cost is quite a bit less
than the Garmin, and you can put it in your old tray.

[Viperdoc]

I have a Garmin 330 and it is a wonderful box. It does have some nice
features like a flight timer, readout of pressure altitude, as well as an
aural alert when leaving an altitude.

However, the most useful item is the Mode S, connected to a box that will
display traffic. Even on severe clear days it is amazing how much traffic is
out there that you will not see. Most of my travels in the Midwest have had
coverage (Chicago, Milwaukee, Indiana, Minneapolis), while some smaller
locations did not (South Bend, for example).

Regardless, for the extra few relative dollars over a regular transponder,
it was definitely worth the cost. It sure beats $20,000 for true TCAS or
TCAD.

[[email protected]]

skym > wrote:
: I'll admit to some lack of knowledge here but, other than the Mode S
: ability of the Garmin 330, aren't xpdrs pretty much just a one trick
: pony? I.e., they just receive a radar signal and reply. Why would a
: Garmin 327 be any better than any other?

That's sorta my thought. Transponders are irritating because they do not do
anything that's *directly* useful to the pilot. They simply allow you to operate in
airspace or get services you otherwise wouldn't be able to. I have no doubt that any
of the new units will function just fine, but bells and whistles on a transponder just
seem kinda silly to me.

The new ones that show pressure altitude are nice, but I've got my encoder
rigged into my VFR GPS, so I can see it there just as well. Push-buttons are nice,
but not worth much extra dollars IMO.

I doubt that I'll be able to do a slide-in replacement because I will want to
add the DME suppression line... which is unavailable on the KT-76's connector.

I haven't heard much good about Narco stuff from lots of people who've had to
deal with service. Maybe that's changed? I do like the fact that they provide
installation information on many items on their webpage. Bendix/King really irritates
me in that respect.

My current thought is to either go with a bare-bones new unit like the Garmin
GTX-320, or maybe an older solid-state unit like the KT-79. That's about the same
vintage as the rest of the radios in my stack (KY-197, KN-53, KNS-80). Reworking the
tray isn't a big deal to me.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Peter Clark]

On Thu, 11 May 2006 12:09:47 +0000 (UTC),
wrote:

>skym > wrote:
>: I'll admit to some lack of knowledge here but, other than the Mode S
>: ability of the Garmin 330, aren't xpdrs pretty much just a one trick
>: pony? I.e., they just receive a radar signal and reply. Why would a
>: Garmin 327 be any better than any other?
>
> That's sorta my thought. Transponders are irritating because they do not do
>anything that's *directly* useful to the pilot. They simply allow you to operate in
>airspace or get services you otherwise wouldn't be able to. I have no doubt that any
>of the new units will function just fine, but bells and whistles on a transponder just
>seem kinda silly to me.
>
> The new ones that show pressure altitude are nice, but I've got my encoder
>rigged into my VFR GPS, so I can see it there just as well. Push-buttons are nice,
>but not worth much extra dollars IMO.
>
> I doubt that I'll be able to do a slide-in replacement because I will want to
>add the DME suppression line... which is unavailable on the KT-76's connector.
>
> I haven't heard much good about Narco stuff from lots of people who've had to
>deal with service. Maybe that's changed? I do like the fact that they provide
>installation information on many items on their webpage. Bendix/King really irritates
>me in that respect.
>
> My current thought is to either go with a bare-bones new unit like the Garmin
>GTX-320, or maybe an older solid-state unit like the KT-79. That's about the same
>vintage as the rest of the radios in my stack (KY-197, KN-53, KNS-80). Reworking the
>tray isn't a big deal to me.

If you really don't care about Mode S get a KT76C. Check with the
shop to be sure but if memory serves it's pin and tray compatible with
the 73 and is just mode C. 5 minute swap.

[Ray Andraka]

wrote:

> Hey all... just got official confirmation that my KT76's power output is way
> low.... classic sign of weak/dying/dead cavity tube. Just looking for suggestions on
> what might be a good, cost-effective replacement. I'm tired of futzing with
> transponders so I'm pretty sure I want a solid-state replacement.
>
> I just had a thought too (for any avionics techs reading)... perhaps the lack
> of DME suppression lead to the premature demise of the KT76? I was going to wire it
> up when I installed the DME, but the KT76 doesn't have that capability. Maybe the DME
> cooked it?
>
> -Cory
>
Nope, the external suppression, on transponders that have it, just
blocks off the transponder reply so that it doesn't send out a reply in
response to the DME interrogation pulses. Its only purpose is to cut
down on unsolicited replies going back to the ATC interrogator.

More likely, your cavity just got tired. The cavity is a tube used to
obtain the required transmit power. When these transponders were new,
it was the only reasonably priced technology available for generating
200W RF power in the frequency range. Being a tube, it eventually
weakens with age.

Most of the new transponders have semiconductor RF amplifiers in the
transmitter. The reply circuits are also completely digital, using
quartz crystals to derive the pulse timing. Transponders of the Narco
AT150 vintage which used resistor-capacitor combinations to generate the
pulse timing for both decode and reply generation, and therefore require
calibration and are prone to drifting out of calibration. Won't happen
with the newer transponders.