Crystal radio receiver: Encyclopedia II - Crystal radio receiver - History

Crystal radio receiver - History

Crystal radio receiver - Early years

People first built and used simple and inexpensive crystal radio sets without batteries or electrical power. Even though vacuum tube radios were common following World War I, crystal radios remained popular, especially among beginning amateur radio enthusiasts, Boy Scouts and school children, who built crystal radios to learn basic electronics and communication.

Early wireless telegraphy used spark gap plasma arc transmitters powered by alternating current generators at frequencies of 400–1000 hertz. When these telegraph keyed Morse code signals were received, the tone or pitch of the generator was clearly heard varying the strength of the radio wave. Varying the strength in this way is called amplitude modulation. As wireless telegraphy became more widely used, the newer radio transmitters employed amplifiers that produced higher power and a tuned signal that required less bandwidth, thus reducing interference.

The first radio telephone transmitters also used amplitude modulation to carry speech and music on a radio wave. The crystal set received these signals almost as well as wireless telegraph signals. AM radio stations today still use amplitude modulation at power levels up to 50 kilowatts on the U.S. broadcast band, and 1 megawatt on shortwave bands. Crystal sets with long wire antennas can still be used today, but their poor selectivity causes signal overlap on crowded broadcast bands.

Crystal radio receiver - 1920s and 1930s

When radio broadcasting became popular in the 1920s, many amateur experimenters bought or constructed crystal sets, often with the tuner inductor coil wound on a tubular oatmeal box or a drinking glass. This led to a series of adventure novels, the Radio Boys books, similar to the Hardy Boys books.

When electronic amplifiers and oscillators were invented, they were almost immediately put into service, rendering crystal sets obsolete first by the much more sensitive vacuum tube regenerative circuit designs and then the highly selective superheterodyne receivers.

During the Great Depression a crystal radio detector could be constructed from an inexpensive or homemade galena crystal and a safety pin. After this detector was connected to steel bedsprings (which doubled as an antenna) and grounded to household cold-water pipes, only inexpensive headphones were needed to listen to the world.

Crystal radio receiver - 1940s

GIs during World War II constructed similar radios from rusty razor blades and pencil lead, the iron oxide crystals of the rust replacing the galena crystal and the graphite of the pencil lead substituting for the safety-pin wire. These crude, but functional, radios were nicknamed foxhole radios.

Crystal radio receiver - Later years

Crystal sets were the most common form of radio listening device for non-professionals in the early 1920s. A century after their first use, hobbyists still build and tinker with— and listen to— crystal radios constructed from just a few parts.

The most common modern design uses a coil for a tuner, and a semiconductor diode instead of a crystal. The output is usually from an earphone speaker. A lengthy antenna wire (15m (40ft) or more) is still helpful to get good sound. A modern design for a "trash radio" is constructed from a tin can and some wire.

In the amateur radio world, particularly amongst QRP operators, crystal recievers are sometimes used in homebrew projects. The most notable is the Pixie2 CW transceiver, an inexpensive kit radio which combines a small crystal-powered transmitter with a crystal reciever attached to a small audio amplifier.

Adapted from the Wikipedia article "History", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki