The purpose of this circuit is to measure the resistance of an antenna at the resonant frequency. The circuit is from an old American documentation for hams.
This circuit, which uses germanium transistors, is from a 1965 English magazine. The used...
Found in a Popular Electronics from the 90s, this circuit operates up to about 5 MHz input....
The transistors in this circuit can be the BC548 and a small speaker serves as a microphone. The...