Circuit of the simplest possible crystal radio receiver. Circuits of this type were used in the first experimental crystal radio receivers in the pioneering days of radio, just after 1900. It consists of a crystal detector (semiconductor diode) DI connected between a long wire antenna and ground, with a sensitive earphone E1 attached across it. The diode rectifies the radio signals picked up by the antenna by conducting the RF current moving in one direction to ground, leaving a pulsing DC voltage across the detector. This extracts the audio signal from the radio frequency carrier wave, and the earphone converts the audio current to sound.   Since it lacks a tuned circuit or any other frequency-selective element besides the broad resonance of the antenna, this circuit has no ability to select a single radio signal to receive, out of all the signals picked up by the antenna. So all radio stations picked up by the antenna are heard simultaneously in the earphone (in practice, the most powerful station usually drowns out the rest).
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