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Morse code is a character encoding for transmitting telegraphic information, using standardized sequences of short and long elements to represent the letters, numerals, punctuation and special characters of a given message. The short and long elements can be formed by sounds, marks or pulses, in on off keying and are commonly known as "dots" and "dashes" or "dits" and "dahs". International Morse code is composed of five elements: short mark, dot or 'dit' (·) — one unit long longer mark, dash or 'dah' (-) — three units long intra-character gap (between the dots and dashes within a character) — one unit long short gap (between letters) — three units long medium gap (between words) — seven units long Morse code can be transmitted in a number of ways: originally as electrical pulses along a telegraph wire, but also as an audio tone, a radio signal with short and long tones, or as a mechanical or visual signal (e.g. a flashing light) using devices like an Aldis lamp or a heliograph. Morse code is transmitted using just two states (on and off) so it was an early form of a digital code. However, it is technically not binary, as the pause lengths are required to decode the information. Originally created for Samuel F. B. Morse's electric telegraph in the early 1840s, Morse code was also extensively used for early radio communication beginning in the 1890s. For the first half of the twentieth century, the majority of high-speed international communication was conducted in Morse code, using telegraph lines, undersea cables, and radio circuits. However, the variable length of the Morse characters made it hard to adapt to automated circuits, so for most electronic communication it has been replaced by more machinable formats, such as Baudot code and ASCII. The most popular current use of Morse code is by amateur radio operators, although it is no longer a requirement for amateur licensing in many other countries. It also continues to be used for specialized purposes, including identification of navigational radio beacon and land mobile transmitters, plus some military communication, including flashing-light semaphore communications between ships in some naval services. Morse code is designed to be easily read by humans without a computer, making it appropriate for sending automated digital data in voice channels, as well as making it ideal for emergency signaling, such as by way of improvised energy sources that can be easily "keyed" by supplying and removing electric power (e.g. by flipping a switch or turning a flashlight on and off). In situations in which the pulse can only be the same length (such as tapping on wood, or on walls of prison cells -- as opposed to an electronic tone), a slightly longer pause between beats can be used in place of a long pulse ("dah"). Development and history Beginning in 1836, Samuel F. B. Morse and Alfred Vail developed an electric telegraph, which sent pulses of electrical current to control an electromagnet that was located at the receiving end of the telegraph wire. The technology available at the time made it impossible to print characters in a readable form, so the inventors had to devise an alternate means of communication. Beginning in 1837, William Cooke and Charles Wheatstone operated electric telegraphs in England, which also controlled electromagnets in the receivers; however, their systems used needle pointers that rotated to indicate the alphabetic characters being sent. In contrast, Morse and Vail's initial telegraph, which first went into operation in 1844, made indentations on a paper tape when an electrical current was transmitted. Morse's original telegraph receiver used a mechanical clockwork to move a paper tape. When an electrical current was received, an electromagnet engaged an armature that pushed a stylus onto the moving paper tape, making an indentation on the tape. When the current was interrupted, the electromagnet retracted the stylus, and that portion of the moving tape remained unmarked. The Morse code was developed so that operators could translate the indentations marked on the paper tape into text messages. In his earliest code, Morse had planned to only transmit numerals, and use a dictionary to look up each word according to the number which had been sent. However, the code was soon expanded to include letters and special characters, so it could be used more generally. The shorter marks were called "dots", and the longer ones "dashes", and the letters most commonly used in the English language were assigned the shortest sequences. In the original Morse telegraphs, the receiver's armature made a clicking noise as it moved into and out of position to mark the tape. Operators soon learned to translate the clicks directly into dots and dashes, making it unnecessary to use the paper tape. When Morse code was adapted to radio, the dots and dashes were sent as short and long pulses. It was later found that people become more proficient at receiving Morse code when it is taught as a language that is heard, instead of one read from a page.To reflect the sound of Morse code, practitioners began to vocalise a dot as "dit", and a dash as "dah". Morse code was an integral part of international aviation. Commercial and military pilots were required to be familiar with it, both for use with early communications systems and identification of navigational beacons which transmitted continuous three letter ID's in Morse code. As late as the 1990s, aeronautical charts listed the three letter ID of each airport in Morse and sectionals still show the Morse signals for Vortac and NDB used for in flight navigation. Morse code was also used as an international standard for maritime communication until 1999, when it was replaced by the Global Maritime Distress Safety System. When the French navy ceased using Morse code in 1997, the final message transmitted was "Calling all. This is our last cry before our eternal silence." See also: 500 kHz |
