This circuit was suggested by Signetics in 1980s documentation. The circuit makes use of the hard-to-obtain component of our day. It is for reference only.
This modulator circuit is nothing more than an audio amplifier that serves to modulate amplitude...
This circuit is from 1995 documentation. When the phone is lifted, the relay closes its contacts by...
The basic idea of this circuit found in a 1988 documentation is to transmit a signal modulated using...