mode c intermittent

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
news
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?