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LORAN
LORAN, short for long range navigation, was a hyperbolic radio navigation system developed in the United States during World War II. It was similar to the UK's Gee system but operated at lower frequencies in order to provide improved range up to with accuracy of tens of miles. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft, but found its main use on the ships and aircraft operating in the Pacific theatre.
LORAN, in its original form, was an expensive system to implement, requiring a cathode ray tube (CRT) display. This limited use to the military and large commercial users. Use was never widespread, and by the time new receivers were available in the 1950s, the same improved electronics led to new systems with higher accuracy. The US Navy began development of Loran-B, which offered accuracy on the order of a few tens of feet, but ran into significant technical problems. The US Air Force had worked on a different concept, known as Cyclan, which the Navy picked up as Loran-C. Loran-C offered longer range than LORAN and accuracy of hundreds of feet. The US Coast Guard took over operations of both systems in 1958.
In spite of the dramatically improved performance of Loran-C, LORAN, now known as Loran-A (or "Standard LORAN"), would become much more popular during this period. This was due largely to the large numbers of surplus Loran-A units released from the Navy as ships and aircraft replaced their sets with Loran-C. The widespread introduction of inexpensive microelectronics during the 1980s caused Loran-C receivers to drop in price dramatically, and Loran-A use began to rapidly decline. Loran-A was dismantled starting in the 1970s; it remained active in North America until 1980 and the rest of the world until 1985. A Japanese chain remained on the air until 9 May 1997, and a Chinese chain was still listed as active as of 2000.
Loran-A used the same frequencies as the amateur radio 160-meter band, and radio operators were under strict rules to operate at reduced power levels; depending on their location and distance to the shore, US operators were limited to maximums of 200 to 500 watts during the day and 50 to 200 watts at night.
==History==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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