A problem with repeaters can be that users will quickly operate the PTT switch on their microphone to see if they can access the repeater, and the repeater will respond with its usual half-second tail. While reassuring to that user, everybody elses suffers from hearing the ‘kerchunk’ emanating from their radios every few minutes. The usual way to combat this problem is to delay the transmitter so that kerchunks don’t have enough time to actually happen. Another approach is to remove the tail from the transmitter, so that users don’t hear a tail from their kerchunk attempt.
Both approaches have problems. The (untried) circuit (created this afternoon by me) above apppears to offer the ideal solution by keying up the transmitter instantly but allowing a half-second tail only after a signal has been received for five seconds.
The diodes can be 1N4148 or similar silicon diodes and the IC should be a 4093 Quad 2 input NAND Schmitt trigger, because some inputs have slowly changing analogue inputs that might result in noise or oscillation as the inputs pass through the ‘linear’ zone.
As I mentioned before, the circuit is untried and untested. In theory, it looks good.
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