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 obtained in a 1980 English magazine, but it can be easily assembled today, since...
This filter was found in Exar documentation from the 1980s. The circuit has an attenuation of 60 dB at the...
This 80's Motorola circuit can generate 100 MHz signals, but they can reach 200 MHz with the...