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