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Letter beacons are radio transmissions of uncertain origin and unknown purpose, consisting of only a single repeating Morse code letter. They have been classified into a number of groups according to transmission code and frequency, and it is supposed that the source for most of them is Russia. (Some beacons sending Morse code letters are well known directional or non-directional beacons for radio navigation. These are not discussed in this article.) Letter beacons have been referred to as: * SLB, or "Single Letter Beacons" * SLHFB, or "Single Letter High Frequency Beacons" * SLHFM, or "Single Letter High Frequency Markers" * Cluster beacons * MX — an ENIGMA〔''E.N.I.G.M.A.'' stands for "European Numbers Information Gathering and Monitoring Association". It was a unique association of radio listeners based in the United Kingdom and active during the 1990s. They issued a printed bulletin every few months, which was mailed to subscribers. All 18 issues of the ENIGMA bulletin contained interesting information about odd and mysterious high frequency transmissions, contributed from radio listeners worldwide. The reception logs were organized, collated and analyzed by the core ENIGMA staff. The coverage was mostly about so-called numbers stations, but there was also some coverage of letter beacons. The ENIGMA bulletins were not archived in libraries and it is difficult to obtain copies today. The major achievement of ENIGMA was the systematic classification and naming of the numerous radio oddities, which were previously described by different and conflicting names in various publications. The original ENIGMA group was disbanded in 2000. In his farewell letter, ENIGMA co-founder Mike G. wrote that all ENIGMA publications and research material would be deposited at the British Library (Boston Spa).〕 and ENIGMA-2000〔(ENIGMA-2000 ) is an internet based community with the same general interests as the old ENIGMA association and with wider coverage of general intelligence matters. This group produces a regular newsletter and maintains the old ENIGMA station naming scheme. ENIGMA-2000 shows less interest in letter beacons than its predecessor.〕 designation. ==Transmission locations== These radio transmissions were discovered in the late 1960s. Their presence became known to the wider amateur radio community in 1978, when beacon “W” started transmitting on 3584 kHz, in the 80 meters band. There is indirect evidence that this particular transmitter was located in Cuba. In 1982 there were also reports, supposedly based on HF direction finding by the US military, that beacon “K” transmitting on 9043 kHz was located at , near the city of Khabarovsk in the USSR. A few years later, it was suggested that the “K” beacons were actually located at Petropavlovsk on the Kamchatka Peninsula and the “U” beacons were located at the Barents Sea coast, between Murmansk and Amderma. According to D.W. Schimmel, in 1986 the Federal Communications Commission (FCC) released the following HF direction finding results for single letter beacons, all of which indicate locations in the USSR:〔 The link with the USSR and, more recently, Russia is further supported by the existence of single letter beacons transmitting letters existing only in the Cyrillic Morse code alphabet. The ENIGMA group also accepted these locations for cluster beacons "C", "D", "P" and "S", adding Vladivostok for beacon "F". A recent source (2006) regarding locations was published on the Web by Ary Boender. This publication also contains an extensive list of letter beacon frequencies, both current and historical. The following locations are given for cluster beacons: For solitary beacons and markers, Boender suggests these locations: Transmissions of the "P" beacon in December 2007, even on medium frequency (420 and 583 kHz), suggest the Russian naval base at Kaliningrad as a possible source. Kaliningrad officially uses the ITU registered call sign RMP. 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「Letter beacon」の詳細全文を読む スポンサード リンク
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