A Voice Squelch for HF and Other SSB Applications
Contributed courtesy of Ken Arck AH6LE


Unlike the standard squelch found in most SSB radios, which respond only to signal levels and therefore are not very good at tracking a varying SSB signal, this design was designed to specifically respond to the human voice while rejecting heterodynes, birdies and other noises. It is basically an FM discriminator that is immune to all non-human speech signals typically found on SSB bands.

This circuit was orginally presented by Frank S. Reid (W9MKV) and David A. Link (W9YAN) in an August 1982 73 Magazine article and is similar in operation to Motorola's Constant SINAD voice squelch circuit used in their MICOMM line of SSB transceivers. Some changes to the original design were made by Jan A. Tarsala (WB6VRN) and Randy Hammock (KC6HUR) in order to accomodate this design into a VOX for retransmission of NASA audio over an FM repeater link. Since we are more interested in using this squelch for SSB work, many of their part value changes have been removed and reverted back to their original values.
The schematic can be found here.


The squelch board is configured as a separate assembly since not everyone will want/need it. All connections from the IRLP HF board are made via a 4 pin connector.

Below you will find the PC layouts if you wish to make your own boards. If there is enough interest, I will make boards available for purchase.

Component placement

Top Trace

Bottom Trace

Parts List