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Radio broadcasting is a one-way wireless transmission over radio waves intended to reach a wide audience. Stations can be linked in radio networks to broadcast a common radio format, either in broadcast syndication or simulcast or both. Audio broadcasting also can be done via cable radio, local wire television networks, satellite radio, and internet radio via streaming media on the Internet. The signal types can be either analog audio or digital audio. In 2009, there were 3,494 radio broadcasting stations in the United States.〔(【引用サイトリンク】title=Radio Broadcasting Report by Pell Research )〕 ==History== The earliest radio stations were simply radiotelegraphy systems and did not carry audio. For audio broadcasts to be possible electronic detection and amplification devices had to be incorporated. The thermionic valve was invented in 1904 by the English physicist John Ambrose Fleming. He developed a device he called an "oscillation valve" (because it passes current in only one direction). The heated filament, or cathode, was capable of thermionic emission of electrons that would flow to the ''plate'' (or ''anode'') when it was at a higher voltage. Electrons, however, could not pass in the reverse direction because the plate was not heated and thus not capable of thermionic emission of electrons. Later known as the Fleming valve, it could be used as a rectifier of alternating current and as a radio wave detector. This greatly improved the crystal set which rectified the radio signal using an early solid-state diode based on a crystal and a so-called cat's whisker. However, what was still required was an amplifier. The triode (mercury-vapor filled with a control grid) was patented on March 4, 1906 by the Austrian Robert von Lieben〔() DRP 179807〕〔Tapan K. Sarkar (ed.) "History of wireless", John Wiley and Sons, 2006. ISBN 0-471-71814-9, p.335〕〔Sōgo Okamura (ed), ''History of Electron Tubes'', IOS Press, 1994 ISBN 90-5199-145-2 page 20〕 independent from that, on October 25, 1906〔() Patent US841387 from 10/25/1906〕〔(U.S. Patent 879,532 )〕 Lee De Forest patented his three-element Audion. It wasn't put to practical use until 1912, when its amplifying ability became recognized by researchers. By about 1920, valve technology had matured to the point where radio broadcasting was fast becoming viable. However, an early audio transmission that could be termed a ''broadcast'' may have occurred on Christmas Eve in 1906 by Reginald Fessenden, although this is disputed.〔Fessenden — The Next Chapter (RWonline.com )〕 While many early experimenters attempted to create systems similar to radiotelephone devices by which only two parties were meant to communicate, there were others who intended to transmit to larger audiences. Charles Herrold started broadcasting in California in 1909 and was carrying audio by the next year. (Herrold's station eventually became KCBS). In The Hague, the Netherlands, PCGG started broadcasting on November 6, 1919, making it, arguably the first commercial broadcasting station. In 1916, Frank Conrad, an electrical engineer employed at the Westinghouse Electric Corporation, began broadcasting from his Wilkinsburg, Pennsylvania garage with the call letters 8XK. Later, the station was moved to the top of the Westinghouse factory building in East Pittsburgh, Pennsylvania. Westinghouse relaunched the station as KDKA on November 2, 1920, as the first commercially licensed radio station in America. The commercial broadcasting designation came from the type of broadcast license; advertisements did not air until years later. The first licensed broadcast in the United States came from KDKA itself: the results of the Harding/Cox Presidential Election. The Montreal station that became CFCF began broadcast programming on May 20, 1920, and the Detroit station that became WWJ began program broadcasts beginning on August 20, 1920, although neither held a license at the time. In 1920 wireless broadcasts for entertainment began in the UK from the Marconi Research Centre 2MT at Writtle near Chelmsford, England. A famous broadcast from Marconi's New Street Works factory in Chelmsford was made by the famous soprano Dame Nellie Melba on 15 June 1920, where she sang two arias and her famous trill. She was the first artist of international renown to participate in direct radio broadcasts. The 2MT station began to broadcast regular entertainment in 1922. The BBC was amalgamated in 1922 and received a Royal Charter in 1926, making it the first national broadcaster in the world. Radio Argentina began regularly scheduled transmissions from the Teatro Coliseo in Buenos Aires on August 27, 1920, making its own priority claim. The station got its license on November 19, 1923. The delay was due to the lack of official Argentine licensing procedures before that date. This station continued regular broadcasting of entertainment and cultural fare for several decades.〔Atgelt, Carlos A. ("Early History of Radio Broadcasting in Argentina." ) The Broadcast Archive (Oldradio.com).〕 Radio in education soon followed and colleges across the U.S. began adding radio broadcasting courses to their curricula. Curry College in Milton, Massachusetts introduced one of the first broadcasting majors in 1932 when the college teamed up with WLOE in Boston to have students broadcast programs.〔http://www.curry.edu〕 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「Radio broadcasting」の詳細全文を読む スポンサード リンク
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