Fixing the Transponder with Duct Tape and Aluminum Foil

On Tue, 9 Mar 2004 19:52:22 -0600, "Joe" wrote:

Why can't you just continue to use what worked? Namely the aluminum foil.

Durability and maintainability are the main issues. This isn't tucked
behind an instrument panel... the radios are mounted in an open-ended box
on the floorboards, and the area is brushed by my right foot when I get
into and out of the airplane. So it has to be something that doesn't tear
easily.

The current foil is basically just crumpled-on and duct-taped in place. If
I have to remove it, it'll just come apart and I'll have to start from
scratch. Plus, I think it was already starting to loosen, etc during the
single flight...interference seemed to be coming back by the end of the
test ride.

I'd rather have something a bit more durable held on with tie-wraps and/or
clamps. My thought is to bend up a hose clamp so it'll snug the new
shielding tight around the square cross-section of the back of the radio,
and tie-wrap it around the existing shielding on the wiring harness. Then,
to remove the radio, all I'll have to do is loosen the clamp and slide back
the shielding to get at the connectors, and slide it back into place and
tighten the clamp when I'm done. If it were aluminum foil, I'd probably
have to completely take it away and fit a new piece, every time.

Finally... since I didn't build this airplane, I have to have an A&P do the
annual inspection every year. He's eventually, essentially, going to have
to sign off my installation as part of the annual. I'd just as soon
present him with a professional-looking job.

But you're right, I'm weird. :-)

Ron "Pay no attention to Marvel Mystery Oil in the Crankcase" Wanttaja

You may have the only known transponder of that variety that has ever been
designed. In the overwhelming predominant world, the test button tests the
receiver only by injecting microwatts of oscillator into the front end.

Jim


(John)
shared these priceless pearls of wisdom:

-Humm, I forgot about that Jim. However most have a self test button
-that causes the transponder to transmit some pulses. I know my 20
-year old Cessna ARC transponder transmits at a low rate when you push
-the test button.
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

So, what does the IDENT button do?

BTW, the comment about the balloon reminded me that what you really need
to do is get your wife mad at you. The roses you have to buy will come
in foil faced mylar already formed into the cone shape you need.

Charlie

Jim Weir wrote:
You may have the only known transponder of that variety that has ever been
designed. In the overwhelming predominant world, the test button tests the
receiver only by injecting microwatts of oscillator into the front end.

Jim


(John)
shared these priceless pearls of wisdom:

-Humm, I forgot about that Jim. However most have a self test button
-that causes the transponder to transmit some pulses. I know my 20
-year old Cessna ARC transponder transmits at a low rate when you push
-the test button.
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Lets see if I got this correct. A micro power oscillator injects RF
pulses into the receiver which then thinks this is a radar
interrogation pulse and fires out a normal TX pulse out of the
transponder.
This sounds very much like what I said befo " I know my 20
year old Cessna ARC transponder transmits at a low rate when you push
the test button."

The ARC RT-359A service manual says that the self test generates 60
MHz 1us pulses that is fed to the first IF amp and that the rest of
the circuit behaves as if it was a normal radar reply. It also says
that you must use a dummy load or an antenna or damage may occur
because it is responding to the self test pulse by transmitting.

I am not sure how King and Narco do the same function since I do not
have a schematic to look at but most likely it is done the same way
which is what you said. It looks like we were both correct.

The end result is that it transmits when you push the self test
button.

On Wed, 10 Mar 2004 08:42:32 -0800, Jim Weir wrote:

You may have the only known transponder of that variety that has ever been
designed. In the overwhelming predominant world, the test button tests the
receiver only by injecting microwatts of oscillator into the front end.

Jim


(John)
shared these priceless pearls of wisdom:

-Humm, I forgot about that Jim. However most have a self test button
-that causes the transponder to transmit some pulses. I know my 20
-year old Cessna ARC transponder transmits at a low rate when you push
-the test button.
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

On Wed, 10 Mar 2004 20:18:37 -0600, Charlie England
wrote:

BTW, the comment about the balloon reminded me that what you really need
to do is get your wife mad at you. The roses you have to buy will come
in foil faced mylar already formed into the cone shape you need.

Geeze, Charlie, she's ALREADY mad at me for spending $2000 for a new
transponder. Better be gold-faced mylar. :-)

Ron "Doghouse" Wanttaja

(John)
shared these priceless pearls of wisdom:

-Lets see if I got this correct. A micro power oscillator injects RF
-pulses into the receiver which then thinks this is a radar
-interrogation pulse and fires out a normal TX pulse out of the
-transponder.

Nope. The transmitter's local oscillator (or a microfragment thereof) is
injected into the receiver's front end. The receiver tests whether or not the
microtransmitter was received.

The transmitter is inhibited by a digital signal during test.

You got it wrong. Sorry.

If you want to carry on this conversation, post your real name and real email
addy.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

From my Terra TRT-250D repair/test manual:
*******************************************
18 Self Test.

18.1 Set interrogation RF level to -90dBm. Hold transponder "Test"
switch in test for at least 4 seconds.

18.2 Observe replies being generated by transponder on % reply meter
of the ATC-1400C/S-1403C. The replies should not exceed 75% over a 5
second period.

18.4 Also observe "T" on display indicating replies being generated.

18.5 Release "Test" switch. Replies should stop.
***********************************************

My comments to clarify some of the above:

1) The ATC-1400C/S-1403C is a transponder test-set.
2) -90 dBm is a level that is well below the receiver threashold (ie,
they don't want the transmitter to "squitter" during this test).


It seems clear to me that the transmitter is indeed transmitting.

Sid Knox
Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ

Jim Weir wrote in message . ..
(John)
shared these priceless pearls of wisdom:

-Lets see if I got this correct. A micro power oscillator injects RF
-pulses into the receiver which then thinks this is a radar
-interrogation pulse and fires out a normal TX pulse out of the
-transponder.

Nope. The transmitter's local oscillator (or a microfragment thereof) is
injected into the receiver's front end. The receiver tests whether or not the
microtransmitter was received.

The transmitter is inhibited by a digital signal during test.

You got it wrong. Sorry.

If you want to carry on this conversation, post your real name and real email
addy.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Jim:
I have the Cessna RT-359A service manual in front of me. There is NO
disabling of the transmitter during self test. In fact several months
ago I watched the voltage on the cathode of the transmitter tube with
a scope and it pulses when the test switch is depressed. There are
only 4 wires and a coax cable to the TX tube. These are Cathode,
filament, anode , ground and RF out. The anode is +1400 volts DC,
the filament is +6.3 volts and ground is of course at ground. The
cathode is pulled to ground by an NPN transistor to transmit.

On page 5-9 paragraph 5-10 step 2 the manual tells you to press the
test switch to measure the TX peak power and frequency of the
transmitter.

King and Narco may or may not disable the transmitter for self test.
I do not have schematics for these transponders so I can not say one
way or the other but I see no reason to do this since it would add
extra circuits and extra cost to do this. They may do this on the
more modern units since the logic may be in an EPLD and no extra
production cost would be incurred to add this small piece of VHDL
code.

I used to have my email address as part of the post but a few months
ago I started to getting 20 to 60 bounced email messages per day that
I had not sent from people I had never heard of. Apparently the
spammers were not only using my email address to spam me at the rate
of 30 to 40 per day they were also spoofing my address on the spam
they were sending. Due to this I now no longer show even a human
readable address but if you insist here it is: frerichsATroDOTcom.
If you want my address and phone number look up airport identifier
AL10. If you email me your phone number I will give you a call and we
can talk about this.
This all started over an EMC question and I am the EMI "expert" where
I work. (The definition of expert is: A drip under pressure.)
John

On Wed, 10 Mar 2004 19:52:48 -0800, Jim Weir wrote:

(John)
shared these priceless pearls of wisdom:

-Lets see if I got this correct. A micro power oscillator injects RF
-pulses into the receiver which then thinks this is a radar
-interrogation pulse and fires out a normal TX pulse out of the
-transponder.

Nope. The transmitter's local oscillator (or a microfragment thereof) is
injected into the receiver's front end. The receiver tests whether or not the
microtransmitter was received.

The transmitter is inhibited by a digital signal during test.

You got it wrong. Sorry.

If you want to carry on this conversation, post your real name and real email
addy.

Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Charlie England wrote in
:

So, what does the IDENT button do?

Just sets a flip/flop so that an extra bit is set on the next reply to an
interrogation (which clears the IDENT flip flop).

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1109-A Shady Lane fax 512-366-4331
Austin, Tx 78721
-----------------------------------------------

Jim...

As I recall, that flipflop triggers a timer (10 seconds???) that sends the ident
bit until timeout. Bose' book confirms what I remember also.

Jim



"James M. Knox"
shared these priceless pearls of wisdom:

-Charlie England wrote in
:
-
- So, what does the IDENT button do?
-
-Just sets a flip/flop so that an extra bit is set on the next reply to an
-interrogation (which clears the IDENT flip flop).
-
------------------------------------------------
-James M. Knox
-TriSoft ph 512-385-0316
-1109-A Shady Lane fax 512-366-4331
-Austin, Tx 78721
------------------------------------------------



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com