We found this circuit in a Poptronics from 1998. The circuit can be extended to more competitors with another 4011. The power can be made with voltages from 6 to 12 V.
We found this circuit in a Popular Electronics from the 90s. It operates at a frequency of 15 kHz....
This circuit for the 27 MHz or 11 meter-band had its assembly described in an article in Radio...
This squelch circuit used in transmitters was found in a magazine for radio amateurs 73 in the...