This code key uses a PLL and an oscillator that generates two frequencies that must be recognized for the relay to be activated. The circuit is from an 80's Popular Electronics.
This simple circuit is from a Radio Electronics from July 1965. The circuit can be assembled with...
Found in the May 1975 issue of Radio Electronics magazine, this circuit turns on after a certain...
We found this circuit in a 1965 General Electric documentation. The circuit generates synchronized...