This circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit was found in Radio Electronics from the 90s. The 4046 is not a common component today.
We found this circuit in an American publication from the 1970s. The MC1555 is the version of the...
This circuit for FET was obtained from a 1977 Radio Handbook. The input impedance is 150 ohm. The...
This is the receiver circuit for the CB13978B, found in the same 1977 Elettronica Prática...