Audio signal operated PTT

Hi, I am looking at making an automatic PTT system for a radio base station i am making, i have seen a few comparator based circuits for sensig nthe audio levels, is this the way to go? I want very prompt on/off times, so i need to have fast rise times etc. Any Ideas?

Most VOX (Voice Operated Switch) circuits clip off the first syllable of a word making speech difficult to understand. They also respond to noise.

responding to noise would be perfect, as this is a bridge to a UHF radio, provided you set the squelch to a proper setting, the only noise to come through will be static. this is only sent through when the radio is active, so might be perfect.

Isn't squelch used in a receiver but not in a transmitter?

audioguru said:

Most VOX (Voice Operated Switch) circuits clip off the first syllable of a word making speech difficult to understand.

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A solution to that would be to add a short audio delay circuit (perhaps a few tenths of a second). That would give the VOX circuit time to turn on the transmitter before the first syllable reaches the transmitter input. Of course this would add complexity to the circuit.

It could perhaps be done with a codec circuit and some RAM or perhaps a lip-sync delay IC.

In the old days you could use a bucket-brigade IC for an audio delay but don't think they are used much anymore. Did find an NTE1641 which apparently is still available with each IC capable of a maximum delay of 51ms.