Found on an 80's Radio Electronics, this circuit is designed to pass the 300 to 34,000 Hz voice range using standard operational amplifiers.
Suggested by Texas Instruments in 1980s documentation, this circuit uses a component of the era....
The idea of this simple circuit is to use a tape recorder to key a transmitter in code emission....
This relay circuit with a dual channel MOSFET (not very common today) was found in an old American...