Found in American documentation from 1968, this circuit has an acute cut-off of the frequency to which it is tuned and which depends on RC. Transistors may be modern equivalents of general use.
Using a common crystal diode and a 741, this circuit can be used to detect microwaves. The circuit is...
The two circuits shown show how to obtain an SSB / CW control for receiving this signal top at a...
The oscillation of the relay causes the applied audio signal to deform and start to resemble the...