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
- Kristallradio.JPG
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.
- Vintage Arrow Germanium Crystal Radio (23708349181).jpg
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.
- Crystal radio receiver block diagram.svg
Block diagram of a crystal radio receiver
- Common crystal radio circuit.svg
Circuit diagram of a simple crystal radio
- CrystalRadio.jpg
Pictorial diagram from 1922 showing the circuit of a crystal radio. This common circuit did not use a tuning capacitor, but used the capacitance of the antenna to form the tuned circuit with the coil. The detector was a cat whisker detector, consisting of a piece of galena with a thin wire in contact with it on a part of the crystal, making a diode contact
- Wire inverted L antenna construction.png
Diagram of an inverted-L antenna, a common wire antenna used with crystal radios
- Simplest crystal radio circuit.svg
The earliest crystal receiver circuit did not have a tuned circuit.
- Crystal radio with impedance matching.svg
Direct-coupled circuit with taps for impedance matching
- Inductively coupled crystal radio circuit.svg
Inductively-coupled circuit with impedance matching. This type was used in most quality crystal receivers in the early 20th century.
Amateur-built crystal receiver with "loose coupler" antenna transformer, Belfast, around 1914
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
