This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even adapted to act as a shield. The circuit has the frequency given by C1 and adjusted in R1.
Using an operational amplifier with FET, this voltmeter has a high input resistance. The circuit has...
This circuit is from 1998 documentation. The coils consist of the number of turns indicated on...
We found this oscillator in a documentation for radio amateurs from the 1970s. The circuit can use...