Found on an 80's Elektor, this circuit uses common components, being the diode a general purpose germanium. The coils select the frequency range of the indicator that reaches 60 MHz.
This circuit was found in an old 1970s telecommunication documentation. It is suitable for...
Suggested by General Electric in a 1967 publication, this circuit makes use of an SCR of the time....
This circuit allows selective relay actuation in the same line according to the applied voltage....