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.
We found this receiver on a single chip in the 1976 Siemens integrated circuits manual. The...
Found in Radio Electronics from the 90s, this circuit has several outputs with different pulse...
We found this circuit in an English publication from the 60's. The transistors are of germanium of the...