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Saturday, January 19, 2013
HISTORY OF MORSE CODE
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. In 1837, William Cooke and Charles Wheatstone began operating electric telegraphs in England that also had electromagnets in the receivers; however, their systems used needle pointers that rotated to indicate the alphabetic characters being sent.
In contrast, Morse's 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 by Alfred Vail 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 sectional charts 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."