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.
The circuit next to a French publication from the 1980s serves as a reference for fluctuating...
This switched-mode circuit was found in the April 1976 issue of Radio Electronics magazine. The...
This circuit "memorizes" the input voltage that is stored in the capacitor and is presented at the...