I'm Going In... Radio Saga Continued...

"Tauno Voipio" wrote:
...
If the sidetone is missing, either the audio path is
broken or the radio does not transmit properly. There
is a slight possibility that the sidetone receiving circuit is
the culprit, but it's so simple that the probability is tiny.

In the current Narco digital stuff, it isn't so simple at all. Can
be cantankerous.

Assuming that the radio behaves in another plane,

I wish I were clear on this, as I thought it works for a while then
doesn't. If heat is causing that, then no assumption can be made
that the stack gets as hot in the other plane. The probable
circuit fault if such the case draws zip, so it doesn't heat up.
It would be other heat, from within and/or external to the box.

Reg,
Fred F.

It is a long shot but consider the possibility that spilled defroster
heat is cooking your radio stack. We had a Narco Com that went south
everytime after a few minutues in flight. We finally found it by using
a shop vac to blow air in the defroster duct & looked for an air leak
under the panel. Sure enough it blew air directly on the radio. Duct
tape etc fixed it.

"Tauno Voipio" wrote in message
...

The intercom and sidetone go different ways:

- the intercom connects the amplified mic signal directly to the
all the headphones,

- the sidetone is created inside the COM radio by receiving
the transmitted signal with a simple detector and feeding
the signal to the headphone line.

That is not true. THe sidetone is generated by taking a sample of the
modulator's output. It is not an RF sniffer.




If the sidetone is missing, either the audio path is broken or
the radio does not transmit properly. There is a slight possibility
that the sidetone receiving circuit is the culprit, but it's so
simple that the probability is tiny.

Assuming that the radio behaves in another plane, I see the
possible causes:

- the power supply to the radio is flaky,

Possible, but if the radio worked fine in another aircraft, it would have
been flaky there also.

- the microphone signal path to the radio is flaky,

Would not explain loss of received signal.


- the audio output path from the radio is flaky,

Most probable.



or
- the antenna connection is broken / shorted.

Would not delete sidetone. I seem to recall in another post that a handheld
at a distance got carrier and not audio. If an antenna transmits, it
listens as well.

Jim