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.
We find this circuit in a Popular Electronics of the 80's. The frequency range depends on C1 and...
With the micro voltage regulator shown in the figure, we can design a power supply for small...
This circuit was found in an old documentation. It converts DC voltages and its maximum current...