This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from 1970s documentation. The components admit equivalents.
This circuit was found in a 1980s US publication. There may be some difficulty in obtaining the...
The circuit shown is from the Motorola Linear Databook of 1990. In the example, the components are for the...
Ideal for benchtop use, this dual-band circuit was obtained from the 1995 Electronics Now...