This circuit was found in a publication in the 1980s. Modern equivalent components can be used. The source must be isolated. The circuit includes an oscillator.
When S1 is pressed, the circuit allows music to be played from an audio source on the telephone line....
This circuit was found in an Experimenters Handbook of the 1990s. The purpose of this circuit is to...
The action of this circuit, found in a 1977 amateur radio documentation, is like to a delay line....