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In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique designation for a transmitting station. In North America they are used as names for broadcasting stations. A call sign can be formally assigned by a government agency, informally adopted by individuals or organizations, or even cryptographically encoded to disguise a station's identity. The use of call signs as unique identifiers dates to the landline railroad telegraph system. Because there was only one telegraph line linking all railroad stations, there needed to be a way to address each one when sending a telegram. In order to save time, two-letter identifiers were adopted for this purpose. This pattern continued in radiotelegraph operation; radio companies initially assigned two-letter identifiers to coastal stations and stations aboard ships at sea. These were not globally unique, so a one-letter company identifier (for instance, 'M' and two letters as a Marconi Station) was later added. By 1912, the need to quickly identify stations operated by multiple companies in multiple nations required an international standard; an ITU prefix would be used to identify a country, and the rest of the call sign an individual station in that country. ==Ships and boats== One of the earliest applications of radiotelegraph operation, long predating broadcast radio, were marine radio stations installed aboard ships at sea. In the absence of international standards, early transmitters constructed after Guglielmo Marconi's first trans-Atlantic message in 1901 were issued arbitrary two-letter calls by radio companies, alone or later preceded by a one-letter company identifier. These mimicked an earlier railroad telegraph convention where short, two-letter identifiers served as Morse code abbreviations to denote the various individual stations on the line (for instance, ''AX'' could represent Halifax). 'N' and two letters would identify US Navy; 'M' and two letters would be a Marconi Station. On April 14, 1912, the RMS Titanic station ''MGY'', busily delivering telegram traffic from ship's passengers to the coastal station at Cape Race, Newfoundland (call sign ''MCE''), would receive warnings of ice fields from Marconi stations aboard the ''M.V. Mesaba'' (call sign ''MMU'') and the ''S.S. Californian'' (call sign ''MWL'').〔http://titanic.marconigraph.com/faqs2.html〕 Its distress call ''CQD CQD CQD CQD CQD CQD DE MGY MGY MGY MGY MGY MGY position 41.44N 50.24W'' would be answered by a station aboard the ''Carpathia'' (call sign ''MPA'').〔(The Titanic radio page ), hf.ro〕 Later that same year, an international conference standardised radio call signs so that the first two letters would uniquely identify a transmitter's country of origin. Merchant and naval vessels are assigned call signs by their national licensing authorities. In the case of states such as Liberia or Panama, which are flags of convenience for ship registration, call signs for larger vessels consist of the national prefix plus three letters (for example, 3LXY, and sometimes followed by a number, i.e. 3LXY2). United States merchant vessels are given call signs beginning with the letters "W" or "K" while US naval ships are assigned callsigns beginning with "N". Originally both ships and broadcast stations were given call signs in this series consisting of three or four letters, but as demand for both marine radio and broadcast call signs grew, gradually American-flagged vessels were given longer call signs with mixed letters and numbers. As broadcast stations became commonplace in the 1920s, some original three and four-letter call signs were reassigned as the corresponding ships were removed from U.S. registry. The WSB call sign had been held by two ships (the ''SS Francis H. Leggett'', shipwrecked off Oregon's coast on September 18, 1914, and later the ''Firwood'', a ship destroyed by fire near Peru on December 18, 1919〔(Broadcast Station Calls With a Past ), WILLIAM FENWICK, Radio Broadcast, July 1928, pg 150 reports the name of this ship as the Firewood, call sign WSB.〕) before being assigned to the ''Atlanta Journal'' for use by its presumably unsinkable Atlanta, Georgia broadcast radio station in 1922. Similarly WEZU, the international radio call sign of the ship SS ''Lash Atlantico'', was assigned in 1997 to a broadcast station. Additional call signs would be reassigned to coastal stations or moved from marine radio to terrestrial broadcast radio when ships were sold for registration to foreign nations, as the new owners would obtain new, local call signs for any existing shipboard radio stations. Leisure craft with VHF radios may not be assigned call signs, in which case the name of the vessel is used instead. Ships in the US wishing to have a radio licence anyway are under F.C.C. class SA: "Ship recreational or voluntarily equipped." Those calls follow the land mobile format of the initial letter K or W followed by 1 or 2 letters followed by 3 or 4 numbers (such as KX0983 or WXX0029). U.S. Coast Guard small boats have a number that is shown on both bows (i.e. port and starboard) in which the first two digits indicate the nominal length of the boat in feet. For example, Coast Guard 47021 refers to the 21st in the series of 47 foot motor lifeboats. The call sign might be abbreviated to the final two or three numbers during operations, for example: ''Coast Guard zero two one''. 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「Call sign」の詳細全文を読む スポンサード リンク
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