[mr spog]

I recently had a discussion with an experience pilot over the radio SQUELCH.
After a radio failiar on return to base we had not been able to transmit anything worthwhile to the nearby airfield but we could hear them.
My argument was the Squelch has absolutely no effect on the transmit; it only cuts out the weaker signals and noise that are received. (Depending on how far the squelch is adjusted. ) He was convinced it weakened the transmissions.
I would be interested to hear comments on this from anyone who is well informed. Not just guesses from people who don't really have a clue.
On a wider issue squelch is something that can cause problems in fight for someone who has not experimented with it. If you have always left it alone because it was set to the right level everytime you flew, you might find yourself in the same situation that I did many years ago; approaching an airfield thinking that your radio was not transmitting when in fact the squelch had somehow been turned up and was cutting out the response from the base station.
It is probably worth a little play with the knob if you have not had a go before!!

[Ian Melville]

My argument was the Squelch has absolutely no effect on the transmit;

Correct, and has no effect on the received signal if the carrier signal is over the threshold set.

Most radios also have a temporary disable of the squelch for testing, pulling the knob, or something similar (no sniggering at the back please )

[HugePilchard]

Effect on transmitting? Nothing. Nada. Zilch.

Squelch is a receive only thing (hence why you'll find a squelch control on some receivers, if it's not an automagic one) - I'd be interested in the logic behind them saying it affects transmissions. As you said, it acts as a sort of variable barrier to weaker transmissions (and noise), only letting stronger signals through. I'd be interested in knowing what their logic is in claiming it affects outward transmissions.

[jollyrog]

I'd be interested in knowing what their logic is in claiming it affects outward transmissions.

I can understand why someone who doesn't know about radios might think this. The intercom squelch stops your voice being heard if you turn it up too high, which could be mistaken for an effect on transmission.

[Ian Melville]

The intercom squelch

Real name is Voice Operated Switch, but more often referred to as VOX

[Keef]

Squelch works only on receive, as others have said. The End.

Voice-operated limiting on intercom is (or should be) disabled when on transmit. It's only to stop microphones feeding ambient noise into the intercom circuit while nobody is speaking.

VOX is a subtly different thing: it's "voice-operated transmit" so that PTT is not required. It's fitted to most amateur transceivers (for example). It would be a bad idea on aircraft, since every time P1 spoke to P2 (or PUT to P!) etc, the exchange would be transmitted.

[Ted.P]

The squelch control (or disable if its automatic) is actually quite useful in flight. If you can't receive a remote ATIS you can often hear it if you disable squelch. Also if you get no response from an FIS some distance away, try disabling squelch.

[Paul_Sengupta]

Voice-operated limiting on intercom is (or should be) disabled when on transmit.

If it isn't, it could affect the transmit if you're not shouting loud enough to break the intercom squelch and get your voice as far as the radio.

But any intercom worth its salt will disable it and put the audio straight through to the radio on transmit. I don't know enough to know what the connections are from the PTT to the intercom though, sorry.