Deep Six Squelch Tails

Kerchunks take a dive with the addition of this audio delay.

Squelch tails are ugly Few things are more annoying to repeater users than a long squelch tail every time someone drops his carrier. At WR3AFM+ a Baltimore Amateur Radio

Club (BARC) multiple-re-

ceive-site repeater,1 this problem is compounded by a second squelch tail, that of the link receiver. The resulting overall squelch tail is approximately 110 milli seconds in duration However, thanks to the circuit described below, it is no longer audible.

A squeich tail is the noise heard at a receiver s audio output after the transmitting station has dropped its carrier but before the receiver's squelch circuit can mute the audio output. I his is what you hear whenever the repeater carrier drops off the air, for example The

Photo A. The completed board installed at WR3AFM> The delay line is in the upper right The 10 connector is in the far right (Photo by N3IC)

duration of the squelch tail is a function of your particular receiver.

Another source of squelch tails is a repeater receiver. Consider first a conventional single-site machine. Whenever the transmitting station drops its carrier, the repeater receiver's output follows wtth a burst of squelch notse Since the repeater transmitter is still on the air at this point, this squelch tail is heard by all stations monitoring the machine

Next, consider a split-site repeater (or a multiple sitt* repeater like WR3AFM) as shown in Fig 1 In this type of setup, the repeater receiver (or each satellite receiver in a multiple-site scheme) is coupled to the repeater transmitter via a link, often on 450 MHz The repeater receiver operates as before, appending a squelch tail to each transmission, The receiver output is sent bv the link transmitter to the repeater transmit site, where it is received by the link receiver When the link transmitter carrier drops, shortly alter the repeater receiver squelch tail ends, the link receiver will append a squelch tail of its own to the audio output. Since the link receiver feeds the repeater transmitter [or voter, in the multiple-site case, which, in turn, feeds the transmitter), this (link) squelch tail also is heard by all monitoring stations.

In order to eliminate the squelch tail nuisance, a delay line was inserted into the audio-signal path To see how this will allow the squelch tail to be silenced.



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