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survival radio
Survival radios are carried by ships and aircraft to facilitate rescue in an emergency. They are generally designed to transmit on international distress frequencies. Maritime systems have been standardized under the Global Maritime Distress Safety System.
==History==
The use of radio to aid in rescuing survivors of accidents at sea came to the forefront after the sinking of the RMS ''Titanic'' in 1912. Lifeboats were equipped with spark gap transmitters such as the Marconi Type 241, c. 1920.〔(MHS | Marconi Collection | Catalogue )〕〔()〕 These operated using Morse code on 500 kHz, the international distress frequency at the time. This frequency had the advantage of long range due to ground-wave propagation and was constantly monitored by all large ships at sea after the'' Titanics sinking. However, due to its wavelength of 600 meters, a long antenna was required to achieve good range. Long wires on the order of 1/4 wavelength held up by kites or balloons were often used. Spark-gap continued to be used in lifeboats long after the technology was banned for general communication.
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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