Found on a 1964 CQ this circuit is intended for tone frequency change modulation (FSK) telegraphic transmissions. It operates with signals of 2.975 and 2.125 Hz.
This circuit is from the 80's, using an integrated of the time. The circuit serves as a reference,...
This circuit was obtained from an American 80's documentation. The operational ones can be...
This logarithmic gain operating configuration was found in the June 1994 Electronics Now magazine. The...