The indicator for this circuit is a 0 to 1 mA milliammeter. The operational is from the 70s, when the circuit was published. Modern equivalent can be used.
This blocking oscillator configuration was found in a 1964 American book. The circuit can be...
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...
This transmitter, indicated for espionage applications, is permanently powered by the power grid....