English: A homemade crystal radio from a do-it-yourself article in a 1925 magazine. A crystal radio is a simple radio that runs on the power of radio waves received by the antenna. It was widely used in the first few decades of the 20th century. The labeled parts in the diagram are: (A) primary winding of tuning coil, (B) secondary winding of tuning coil (C) variable tuning capacitor, (D) galena cat's whisker detector, (E) bypass capacitor, (F) panel with dial capacitor is attached to, (G) breadboard, (1,2) binding posts for antenna and ground wire, (3,4) binding posts for earphones.