Crystal radio
A crystal radio, sometimes called a crystal set, is a very simple AM (or rarely FM) radio receiver, that does not need batteries to work. A long wire antenna gathers enough of the radio signals from nearby transmitters to power a crystal diode, which demodulates the signals, and plays them as sound through an earphone or small headset.
Crystal radios have come and gone many times in history. They were built in the early days of radio broadcasting by amateurs, and people who could not afford a well-made radio. They became popular again during the Great Depression, when money was scarce. During World War II, American soldiers built "foxhole radios" that used a razor blade and pencil point instead of a crystal. (German and Italian troops had equipment to detect normal superheterodyne radio receivers working, so an alternate choice was a wise one.)
After the war ended, amateurs built more crystal sets, and children began to make them as science and hobby projects. Later during the Vietnam War prisoners of war again built simple radios, and soldiers used Slinky springs as antennas.
Hobby clubs still exist, that give information to persons who want to build a crystal radio or similar radio project.
Crystal Radio Media
Swedish crystal radio from 1922 made by Radiola, with earphones. The device at top is the radio's cat's whisker detector. A second pair of earphone jacks is provided.
1970s-era Arrow crystal radio marketed to children. The earphone is on left. The antenna wire, right, has a clip to attach to metal objects such as a bedspring, which serve as an additional antenna to improve reception.
A family listening to a crystal radio in the 1920s
Greenleaf Whittier Pickard's US Patent 836,531 "Means for receiving intelligence communicated by electric waves" diagram
US Bureau of Standards 1922 Circular 120 "A simple homemade radio receiving outfit" taught Americans how to build a crystal radio.
Type 'C' Form 'A' twin detector crystal radio set, manufactured by British Thomson Houston Ltd. in 1924, kept at the Museum of the radio - Monteceneri (Switzerland)
"Foxhole radio" used on the Italian Front in World War 2. It uses a pencil lead attached to a safety pin pressing against a razor blade for a detector.
Crystal radio used as a backup receiver on a World War II Liberty ship
Block diagram of a crystal radio receiver
Circuit diagram of a simple crystal radio
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Other websites
- Stay Tuned
- Xtal Set Society Archived 2006-01-14 at the Wayback Machine
- Foxhole Radio article at Bizarre Stuff Archived 2008-05-31 at the Wayback Machine
