Howdy,
I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder. Mode C is intermittent with ATC. Is it more than likely this is an altimeter problem or transponder problem? Sometimes when it is not reporting, i cycle the transponder off then back on and it starts reporting again. That works about 30 percent of the time, if that much. Thanks in advance,
Brian
Also, sould an aeromech and aerosonic encoding altimeter interchange as far as the connections are concerned?

In article >,
skyav8r > wrote:

> Howdy,
> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
> Mode C is intermittent with ATC. Is it more than likely this is an
> altimeter problem or transponder problem? Sometimes when it is not
> reporting, i cycle the transponder off then back on and it starts
> reporting again. Thanks in advance,
> Brian
> Also, sould an aeromech and aerosonic encoding transponder interchange
> as far as the connections are concerned?

Check for oil/dirt buildup on the TXP antenna. THere is usually a lot of
carbon in that stuff -- it can short out the antenna on Xmt.

--
Remove _'s from email address to talk to me.

On Sep 3, 5:32*pm, skyav8r > wrote:
> Howdy,
> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
> Mode C is intermittent with ATC. Is it more than likely this is an
> altimeter problem or transponder problem? Sometimes when it is not
> reporting, i cycle the transponder off then back on and it starts
> reporting again. Thanks in advance,
> Brian
> Also, sould an aeromech and aerosonic encoding transponder interchange
> as far as the connections are concerned?

I've had this problem. Luckily each time its been right before our IFR
cert. My avionics guy says that there is some timing thing in the
transponder and it gets out of sync making it intermitant. The
avionics guy can tune it up and it will work great.

-Robert

I had a similar problem in mine, then it got worse. Trouble was whenever
it was in the shop, it was working. Finally some guy thought to gently
heat gun the thing and found the failed part. I think it was a capacitor
that when warm, stopped working. It's had other problems too, like that
expensive final transistor going.

Just my experience....

John

skyav8r wrote:
> Howdy,
> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
> Mode C is intermittent with ATC. Is it more than likely this is an
> altimeter problem or transponder problem? Sometimes when it is not
> reporting, i cycle the transponder off then back on and it starts
> reporting again. Thanks in advance,
> Brian
> Also, sould an aeromech and aerosonic encoding transponder interchange
> as far as the connections are concerned?
>
>
>
>

"Orval Fairbairn" > wrote in message
...
> In article >,
> skyav8r > wrote:
>
>> Howdy,
>> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
>> Mode C is intermittent with ATC. Is it more than likely this is an
>> altimeter problem or transponder problem? Sometimes when it is not
>> reporting, i cycle the transponder off then back on and it starts
>> reporting again. Thanks in advance,
>> Brian
>> Also, sould an aeromech and aerosonic encoding transponder interchange
>> as far as the connections are concerned?
>
> Check for oil/dirt buildup on the TXP antenna. THere is usually a lot of
> carbon in that stuff -- it can short out the antenna on Xmt.

This is the most common problem and should always be checked first. The
radar sensor interrogates Mode3 2-3 more times for every ModeC
interrogation. So poor reception/transmission will show up on ModeC first.

I clean my antenna at every oil change, but my plane throws off almost no
oil. The more oil your plane goes through, the more often you should clean
the antenna.

The Visitor wrote:
> I had a similar problem in mine, then it got worse. Trouble was whenever
> it was in the shop, it was working. Finally some guy thought to gently
> heat gun the thing and found the failed part. I think it was a capacitor
> that when warm, stopped working. It's had other problems too, like that
> expensive final transistor going.
>
> Just my experience....
>
> John
>
> skyav8r wrote:
>> Howdy,
>> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
>> Mode C is intermittent with ATC. Is it more than likely this is an
>> altimeter problem or transponder problem? Sometimes when it is not
>> reporting, i cycle the transponder off then back on and it starts
>> reporting again. Thanks in advance,
>> Brian
>> Also, sould an aeromech and aerosonic encoding transponder interchange
>> as far as the connections are concerned?


The KT76 transmitter is a free-running electron-tube
oscillator built into a cavity resonator. The frequency
of the sent signal is dependent on the cavity and
electron tube properties.

When the tube gets old, its properties start drifting
around, and the transmitter frequency follows the
drift. The thing stays on channel for short while
after tuning and then gets off again.

The cure is the change of the transmitter module. The
tube cannot be changed from the cavity alone.

--

Tauno Voipio (CPL and avionics engineer)
tauno voipio (at) iki fi

"Tauno Voipio" > wrote in message
...
> The Visitor wrote:
>> I had a similar problem in mine, then it got worse. Trouble was whenever
>> it was in the shop, it was working. Finally some guy thought to gently
>> heat gun the thing and found the failed part. I think it was a capacitor
>> that when warm, stopped working. It's had other problems too, like that
>> expensive final transistor going.
>>
>> Just my experience....
>>
>> John
>>
>> skyav8r wrote:
>>> Howdy,
>>> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
>>> Mode C is intermittent with ATC. Is it more than likely this is an
>>> altimeter problem or transponder problem? Sometimes when it is not
>>> reporting, i cycle the transponder off then back on and it starts
>>> reporting again. Thanks in advance,
>>> Brian
>>> Also, sould an aeromech and aerosonic encoding transponder interchange
>>> as far as the connections are concerned?
>
>
> The KT76 transmitter is a free-running electron-tube
> oscillator built into a cavity resonator. The frequency
> of the sent signal is dependent on the cavity and
> electron tube properties.
>
> When the tube gets old, its properties start drifting
> around, and the transmitter frequency follows the
> drift. The thing stays on channel for short while
> after tuning and then gets off again.
>
> The cure is the change of the transmitter module. The
> tube cannot be changed from the cavity alone.

If that were the case he would be having trouble with Mode3 also, and he
only indicated problems with ModeC.

Well that is probably what they changed out for me one time it totally
failed. It was very expensive. Almost the cost of a new (different
brand) transponder. Now for new aircraft, dual transponders are the way
to go.

John

"The Visitor" > wrote

> Now for new aircraft, dual transponders are the way to go.

Perhaps I am missing something obvious, but why would you need (or want) two
transponders for new aircraft?
--
Jim in NC

In article >,
"Morgans" > wrote:

> "The Visitor" > wrote
>
> > Now for new aircraft, dual transponders are the way to go.
>
> Perhaps I am missing something obvious, but why would you need (or want) two
> transponders for new aircraft?

Required if you fly above FL180 isn't it?

"John Smith" > wrote in message
...
> In article >,
> "Morgans" > wrote:
>
>> "The Visitor" > wrote
>>
>> > Now for new aircraft, dual transponders are the way to go.
>>
>> Perhaps I am missing something obvious, but why would you need (or want)
>> two
>> transponders for new aircraft?
>
> Required if you fly above FL180 isn't it?

No.

"John Smith" > wrote
>
> Required if you fly above FL180 isn't it?

Sorry, but I don't normally think in terms of being "that high" above the
ground, unless it is in a long metal tube with only a couple tubes hung
below the wings. <g>

What is required at that altitude, and won't that one work down low with the
rest of us piston powered mortals?
--
Jim in NC

In article >,
John Smith > wrote:

> > Perhaps I am missing something obvious, but why would you need (or want)
> > two
> > transponders for new aircraft?
>
> Required if you fly above FL180 isn't it?

Do have a FAR reference for that?

--
Bob Noel
(goodness, please trim replies!!!)

Especially for new. A second one is a negligible cost increase. To have
a transponder fail enroute, is a real problem these days. When mine was
giving me grief it really messed up my trip. I would put a second one in
my seneca but I will soon be ordering a new plane and it will have dual
transponders. I don't fly vfr when on lnog trips.

John

Morgans wrote:
> "The Visitor" > wrote
>
>
>>Now for new aircraft, dual transponders are the way to go.
>
>
> Perhaps I am missing something obvious, but why would you need (or want) two
> transponders for new aircraft?

On Fri, 05 Sep 2008 22:50:53 -0400, Bob Noel
> wrote:

>In article >,
> John Smith > wrote:
>
>> > Perhaps I am missing something obvious, but why would you need (or want)
>> > two
>> > transponders for new aircraft?
>>
>> Required if you fly above FL180 isn't it?
>
>Do have a FAR reference for that?

91.215(b)(1) requires transponders in class A airspace. What I've
seen is that most pressurized aircraft and turbines in general have
tow installed - does ATC routinely bounce you out of class A with inop
transponders, thus the commonality of 2 in those applications? Can't
seem to find a requirement for dual installations tho.

"Peter Clark" > wrote in message
...
> On Fri, 05 Sep 2008 22:50:53 -0400, Bob Noel
> > wrote:
>
>>In article >,
>> John Smith > wrote:
>>
>>> > Perhaps I am missing something obvious, but why would you need (or
>>> > want)
>>> > two
>>> > transponders for new aircraft?
>>>
>>> Required if you fly above FL180 isn't it?
>>
>>Do have a FAR reference for that?
>
> 91.215(b)(1) requires transponders in class A airspace. What I've
> seen is that most pressurized aircraft and turbines in general have
> tow installed - does ATC routinely bounce you out of class A with inop
> transponders, thus the commonality of 2 in those applications? Can't
> seem to find a requirement for dual installations tho.

They can, but probably won't. ATC can still track a target radar only so
long as coverage permits, although there will be no altitude displayed and
must be queried.

skyav8r wrote:

> Howdy,
> I have an Aeromech 8140B20 encoding altimeter with a KT76 transponder.
> Mode C is intermittent with ATC. Is it more than likely this is an
> altimeter problem or transponder problem? Sometimes when it is not
> reporting, i cycle the transponder off then back on and it starts
> reporting again. Thanks in advance,
> Brian
> Also, sould an aeromech and aerosonic encoding transponder interchange
> as far as the connections are concerned?
>
>
>
>
Old encoders do go intermittent. I finally replaced mine to cure the
problem. But mine would not always come back alive upon a recycle, or it
would report all sorts of weird altitudes to ATC.

I bought another transponder on e-bay to try a "swap test". When swapped
the problem persisted. You might try swapping with an airport buddy who
has the same unit to try to cheaply isolate the problem. Since these
units slide out of their trays, the swap is usually easy.

If it is the encoder, you of course have to replace or overhaul the
altimeter, which I believe may be a bit more costly.

Good Luck,
Mike