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The International Telecommunication Union (ITU) allocates call sign prefixes for radio and television stations of all types. They also form the basis for, but do not exactly match, aircraft registration identifiers. These prefixes are agreed upon internationally, and are a form of country code. A call sign can be any number of letters and numerals but each country must only use call signs that begin with the characters allocated for use in that country. A few countries do not fully comply with these rules. Australian broadcast stations officially have—but do not use—the VL prefix, and Canada uses Chile's CB for its own Canadian Broadcasting Corporation stations. This is through a special agreement with the government of Chile, which is officially assigned the CB prefix. With regard to the second and/or third letters in the prefixes in the list below, if the country in question is allocated all callsigns with A to Z in that position, then that country can also use call signs with the digits 0 to 9 in that position. For example, the United States is assigned KA–KZ, and therefore can also use prefixes like KW0 or K1. Many large countries in turn have internal rules on how and where specific subsets of their callsigns can be used (such as Mexico's XE for AM and XH for FM radio and television broadcasting), which are not covered here. ==Unallocated and unavailable call sign prefixes== Unallocated: The following call sign prefixes are available for future allocation by the ITU. (''x'' represents any letter; ''n'' represents any digit from 2–9.) * E8, E9, H5, J9, S4, T9 *, U''n'', V9, X''n'', YZ *, Z4–Z7, Z9, 4N *. ( * Indicates a prefix that has recently been returned to the ITU.) Unavailable: Under present ITU guidelines the following call sign prefixes shall not be allocated .〔http://life.itu.int/radioclub/rr/res-13.pdf〕 They are sometimes used unofficially - such as amateur radio operators operating in a disputed territory or in a nation state that has no official prefix (e.g. S0 in Western Sahara or station 1A0 at Knights of Malta headquarters in Rome). (''x'' represents any letter; ''n'' represents any digit from 2–9.) * ''nn'', ''x''0, ''x''1, 0''x'', 1''x'', Q''x''. * no prefixes beginning with Q are used—they may be confused with Q codes. * no prefixes with the digits 1 or 0 are used—they may be confused with the letters I or O. * two digit prefixes (''nn'') are not as yet considered by the ITU. 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「ITU prefix」の詳細全文を読む スポンサード リンク
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