Crystal radio

A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena. This component is now called a diode. A crystal radio receiver, also called a crystal set, is a simple radio receiver, popular in the early days of radio. It uses only the power of the received radio signal to produce sound, needing no external power. It is named for its most important component, a crystal detector, originally made from a piece of crystalline mineral such as galena. This component is now called a diode. Crystal radios are the simplest type of radio receiver and can be made with a few inexpensive parts, such as a wire for an antenna, a coil of wire, a capacitor, a crystal detector, and earphones. However they are passive receivers, while other radios use an amplifier powered by current from a battery or wall outlet to make the radio signal louder. Thus, crystal sets produce rather weak sound and must be listened to with sensitive earphones, and can only receive stations within a limited range. The rectifying property of a contact between a mineral and a metal was discovered in 1874 by Karl Ferdinand Braun. Crystals were first used as a detector of radio waves in 1894 by Jagadish Chandra Bose, in his microwave optics experiments. They were first used as a demodulator for radio communication reception in 1902 by G. W. Pickard. Crystal radios were the first widely used type of radio receiver, and the main type used during the wireless telegraphy era. Sold and homemade by the millions, the inexpensive and reliable crystal radio was a major driving force in the introduction of radio to the public, contributing to the development of radio as an entertainment medium with the beginning of radio broadcasting around 1920. Around 1920, crystal sets were superseded by the first amplifying receivers, which used vacuum tubes. They became obsolete for commercial use but continued to be built by hobbyists, youth groups, and the Boy Scouts mainly as a way of learning about the technology of radio. They are still sold as educational devices, and there are groups of enthusiasts devoted to their construction. Crystal radios receive amplitude modulated (AM) signals, and can be designed to receive almost any radio frequency band, but most receive the AM broadcast band. A few receive shortwave bands, but strong signals are required. The first crystal sets received wireless telegraphy signals broadcast by spark-gap transmitters at frequencies as low as 20 kHz. Crystal radio was invented by a long, partly obscure chain of discoveries in the late 19th century that gradually evolved into more and more practical radio receivers in the early 20th century. The earliest practical use of crystal radio was to receive Morse code radio signals transmitted from spark-gap transmitters by early amateur radio experimenters. As electronics evolved, the ability to send voice signals by radio caused a technological explosion around 1920 that evolved into today's radio broadcasting industry. Early radio telegraphy used spark gap and arc transmitters as well as high-frequency alternators running at radio frequencies. The coherer was the first means of detecting a radio signal. These, however, lacked the sensitivity to detect weak signals. In the early 20th century, various researchers discovered that certain metallic minerals, such as galena, could be used to detect radio signals. Indian physicist Jagadish Chandra Bose was first to use a crystal as a radio wave detector, using galena detectors to receive microwaves starting around 1894. In 1901, Bose filed for a U.S. patent for 'A Device for Detecting Electrical Disturbances' that mentioned the use of a galena crystal; this was granted in 1904, #755840. On August 30, 1906, Greenleaf Whittier Pickard filed a patent for a silicon crystal detector, which was granted on November 20, 1906.