I. Earphone radio
This radio consists of only four parts. Two wires, a crystal diode, and an old telephone earphone.
Construction: Set the two wires on the taps, and a diode connecting them. Therewith it is ready. You only have to put to earth, and span the antenna. It is strange by the earphone. Its metal carcase functions as a capacitor. They form an oscillator tank with the spool in the earphone. It works in the amplitude-modulated waveband. As the radio is untuneable, it broadcasts the programme, which has the largest field strength. In Hungary this is the Radio Kossuth.