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A crystal radio receiver, also called a crystal set or cat's whisker receiver, is a very simple radio receiver, popular in the early days of radio. It needs no other power source but that received solely from the power of radio waves received by a wire antenna. It gets its name from its most important component, known as a crystal detector, originally made from a piece of crystalline mineral such as galena.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 copper wire for adjustment, a capacitor, a crystal detector, and earphones. They are distinct from ordinary radios as they are passive receivers, while other radios use a separate source of electric power such as a battery or the mains power to amplify the weak radio signal so as to make it 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 crystals was discovered in 1874 by Karl Ferdinand Braun, and crystal detectors were developed and applied to radio receivers in 1904 by Jagadish Chandra Bose,〔Bose was first to use a crystal as a radio wave detector, using galena detectors to receive microwaves starting around 1894 and receiving a patent in 1904. 〕〔(Sarkar (2006) ''History of wireless'', p.94, 291-308 )〕 G. W. Pickard〔 on (Stay Tuned website )〕 and others. Crystal radios were the first widely used type of radio receiver, and the main type used during the wireless telegraphy era.〔crystal detectors were used in receivers in greater numbers than any other type of detector after about 1907. 〕 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 around 1920. After about 1920, crystal sets were superseded by the first amplifying receivers, which used vacuum tubes (Audions), and became obsolete for commercial use.〔 They, however, continued to be built by hobbyists, youth groups, and the Boy Scouts as a way of learning about the technology of radio. Today they are still sold as educational devices, and there are groups of enthusiasts devoted to their construction〔Jack Bryant (2009) (Birmingham Crystal Radio Group ), Birmingham, Alabama, US. Retrieved 2010-01-18.〕〔(The Xtal Set Society ) midnightscience.com . Retrieved 2010-01-18.〕〔Darryl Boyd (2006) (Stay Tuned Crystal Radio website ) . Retrieved 2010-01-18.〕〔Al Klase (Crystal Radios ), Klase's (SkyWaves ) website . Retrieved 2010-01-18.〕〔Mike Tuggle (2003) (Designing a DX crystal set ) (Antique Wireless Association ) journal . Retrieved 2010-01-18.〕〔Rainer Steinfuehr (2009) (Gollum´s Crystal Receiver World ) ''(Wumpus's Old Radio World )'' website, Berlin, Germany. Retrieved 2010-01-18.〕 who hold competitions comparing the performance of their home-built designs.〔(Elmer Memorial Crystal Radio DX Contest ), sponsored by (Birmingham Crystal Radio Group ), Birmingham, Alabama, US. Retrieved 2010-01-18.〕〔(Crystal Radio Building Contest ), by (The Xtal Set Society ) midnightscience.com . Retrieved 2010-01-18.〕 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.〔Long distance transoceanic stations of the era used wavelengths of 10,000 to 20,000 meters, correstponding to frequencies of 15 to 30 kHz.〕 == History == 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; it constitutes the origin of the field of electronics. 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 in the years around 1920 that evolved into today's radio broadcasting industry. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crystal radio」の詳細全文を読む スポンサード リンク
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