Crystal radio

A simple radio receiver that uses a crystal detector to demodulate radio signals, typically without a battery or powered amplifier.

Crystal detector: A rectifying device that detects radio signals, often using a metal point touching a semiconductor crystal. It rectifies the tuned radio-frequency signal so its audio modulation can be heard.
Resonance: A system's enhanced response when driven near one of its natural frequencies. Resonance explains why the receiver favors one station's carrier frequency.
Jagadish Chandra Bose: An Indian physicist whose experiments included early semiconductor detectors for radio waves. His radio experiments used galena and other materials as sensitive detectors.
AM broadcasting: Radio broadcasting that commonly sends audio by varying a carrier's amplitude. Strong local AM stations are especially suited to simple crystal reception.
Tuned circuit: An electrical circuit that selects a desired frequency through resonance. Its resonant frequency determines which station the receiver selects.
Rectifier: A device or circuit that allows current to flow more readily in one direction than the other. The crystal detector is a simple rectifier, not a powered amplifier.
Greenleaf Whittier Pickard: An American radio pioneer who developed and patented silicon crystal detectors. His detector work helped establish the practical crystal receiver.
Long-distance radio reception: Reception of radio transmissions over distances beyond ordinary local coverage. A crystal set can receive distant stations under favorable propagation and antenna conditions.
Amplitude modulation: A method of encoding information by varying a carrier wave's amplitude. The detector recovers audio from the carrier's changing amplitude.
Radio frequency: The portion of the electromagnetic spectrum used for radio communication. The tuned circuit selects a radio-frequency carrier before detection.

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