INTRODUCTION
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.
CONSTRUCTION NOTES
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.
