With this system you can disconnect phone lines in case of need for protection. The circuit is from a 1989 documentation working only with analog lines.
This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics...
The frequency in this circuit is adjusted by P1 and given by C1. Short pulses, as the ones...
This Hartley telegraphy oscillator operates with the transmitter signal generating a tone in a...