Placed near a common receiver, this oscillator is intended to generate a beating signal to receive RTTY or SSB communications. The circuit is from old telecommunications documentation.
This is one of many zero crossing detector that can be found in this section. It was found in...
This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent...
Placed in the vicinity of a telegraphic transmitter (CW), this circuit produces an audible signal on...