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Loran-C
Loran-C is a hyperbolic radio navigation system which allows a receiver to determine its position by listening to low frequency radio signals transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to provide a signal that was both long-range and highly accurate, traits that had formerly been at odds. The downside was the expense of the equipment needed to interpret the signals, which meant that Loran-C was used primarily by militaries after it was first introduced in 1957.
By the 1970s the electronics needed to implement Loran-C had been dramatically reduced due to the introduction of solid state radio electronics, and especially the use of early microcontrollers to interpret the signal. Low-cost and easy-to-use Loran-C units became common from the late 1970s, especially in the early 1980s, leading to the earlier LORAN〔The original system was known as LORAN, a short-form for LOng RAnge Navigation. Operation of the system, and the newly introduced Loran-C system, were handed to the Coast Guard in 1958. They took the time to retroactively change the name of the original system to Loran-A, and used lower-case naming from then on. See Gatterer, p. xi.〕 system being turned off in favour of installing more Loran-C stations around the world. Loran-C became one of the most common and widely used navigation systems for large areas of North America, Europe, Japan and the entire Atlantic and Pacific areas. The Soviet Union operated a nearly identical system, CHAYKA.
The introduction of civilian satellite navigation in the 1990s led to a very rapid drop-off in Loran-C use. Discussions about the future of Loran-C began in the 1990s, and several turn-off dates were announced and then cancelled. In 2010 the US and Canadian systems were shut down, along with shared Loran-C/CHAYKA stations with Russia.〔〔 Several other chains remain active, and some have been upgraded for continued use.
==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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