This circuit was found in the January 1991 issue of Radio Electronics magazine. The circuit uses integrated circuits of the time and the coils depend on the tuned bands.
This version of the circuit is from 2000, using a source of negative voltage that allows to obtain...
This somewhat complex circuit was found in the May 1984 issue of Radio Electronics magazine. The...
This basic circuit is from an old documentation. The relay must be 50 mA maximum and must have a...