A cat's whisker is a thin, adjustable wire that lightly touches a piece of galena or another mineral to form a primitive point-contact diode. By manually moving the wire to find a sensitive spot on the crystal, the user creates a junction that rectifies alternating current radio signals into direct current audio. This mechanism formed the basis of early crystal radio sets before sealed semiconductor diodes became standard.
Heard on the job
I spent twenty minutes adjusting the cat's whisker on this replica radio just to pick up a faint AM station.
Insider tip
Finding the sweet spot on the crystal requires a very light touch, as too much pressure destroys the rectifying properties of the junction.