It actually consists of a tunable field strength meter. The circuit is of an old documentation and the circuit must be tuned to the frequency to be monitored. The circuit offers the option to use a headset.
This 1 to 40 MHz amplifier is from a 1969 Motorola documentation. The components are of the time...
This useful benchtop power supply uses a single LM350 integrated circuit as a regulator. The...
Found in an EDN this 80's circuit allows a microcontroller to be used to regulate a battery. The...