Morse code

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Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment. The International Morse Code encodes the Roman alphabet, the Arabic numerals and a small set of punctuation and procedural signals as standardized sequences of short and long "dots" and "dashes", or "dits" and "dahs". Because many non-English natural languages use more than the 26 Roman letters, extensions to the Morse alphabet exist for those languages.

Morse code speed is specified in words per minute (WPM) and associated with an "element time" equal to 1.2 seconds divided by the speed in WPM. A dot consists of an "on" element followed by an "off" element, and a dash is three "on" elements and one "off" element. Each character is a sequence of dots and dashes, with the shorter sequences assigned to the more frequently used letters in English – the letter 'E' represented by a single dot, and the letter 'T' by a single dash. A speed of 12 WPM is therefore associated with an element time of 100 milliseconds, so each dot is 100 ms long and each dash is 300 ms long, each followed by 100 ms of silence.

A related but different code was originally created for Samuel F. B. Morse's electric telegraph in the early 1840s. In the 1890s it began to be extensively used for early radio communication before it was possible to transmit voice. In the early part of the twentieth century, most high-speed international communication used Morse code on telegraph lines, undersea cables and radio circuits. However, on-off keying, variable character lengths, the limited character set and the lack of forward error correction are inefficient and poorly suited to computer reception, so machine-to-machine communication generally uses frequency shift keying (FSK) or phase shift keying (PSK) and encodes text in the Baudot, ASCII and Unicode character sets.

Morse code is most popular among amateur radio operators although it is no longer required for licensing in most countries, including the US. Pilots and air traffic controllers are usually familiar with Morse code and require a basic understanding. Aeronautical navigational aids, such as VORs and NDBs, constantly identify in Morse code.

Because it can be read by humans without a decoding device, Morse is sometimes a useful alternative to synthesized speech for sending automated digital data to skilled listeners on voice channels. Many amateur radio repeaters, for example, identify with Morse even though they are used for voice communications.

For emergency signals, Morse code can be sent by way of improvised sources that can be easily "keyed" on and off, making it one of the simplest and most versatile methods of telecommunication.

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