- Terminology related to character encoding
.svg)
Procedural signs or prosigns are shorthand signals used in Morse code radio telegraphy procedure, for the purpose of simplifying and standardizing radio communication protocol. They are separate from Morse code abbreviations, which consist mainly of brevity codes that convey messages to other parties with greater speed and accuracy.
See also
| EEEEE | Erase sign | ▄ ▄ ▄ ▄ ▄ | Exactly five dots (code for numeral 5). Replaced by HH (exactly eight, EEEEEEEE). |
| RRRRR | Receipt sign | ▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄ | Replaced by R. |
| e | Further message sign | ▄ ▄ ▄▄▄ ▄ ▄ | Re-purposed original ITU symbol for É not used in English. |
Character sets, character maps and code pages
Historically, the terms "character encoding", "character map", "character set" and "code page" were synonymous in computer science, as the same standard would specify a repertoire of characters and how they were to be encoded into a stream of code units – usually with a single character per code unit. But now the terms have related but distinct meanings,[9] due to efforts by standards bodies to use precise terminology when writing about and unifying many different encoding systems.[8] Regardless, the terms are still used interchangeably, with character set being nearly ubiquitous.
A "code page" usually means a byte-oriented encoding, but with regard to some suite of encodings (covering different scripts), where many characters share the same codes in most or all those code pages. Well-known code page suites are "Windows" (based on Windows-1252) and "IBM"/"DOS" (based on code page 437), see Windows code page for details. Most, but not all, encodings referred to as code pages are single-byte encodings (but see octet on byte size.)
IBM's Character Data Representation Architecture (CDRA) designates entities with coded character set identifiers (CCSIDs), each of which is variously called a "charset", "character set", "code page", or "CHARMAP".[8]
The term "code page" does not occur in Unix or Linux where "charmap" is preferred, usually in the larger context of locales.
In contrast to a "coded character set", a "character encoding" is a map from abstract characters to code words. A "character set" in HTTP (and MIME) parlance is the same as a character encoding (but not the same as CCS).
"Legacy encoding" is a term sometimes used to characterize old character encodings, but with an ambiguity of sense. Most of its use is in the context of Unicodification, where it refers to encodings that fail to cover all Unicode code points, or, more generally, using a somewhat different character repertoire: several code points representing one Unicode character,[10] or versa (see e.g. code page 437). Some sources refer to an encoding as legacy only because it preceded Unicode.[11] All Windows code pages are usually referred to as legacy, both because they antedate Unicode and because they are unable to represent all 221 possible Unicode code points.
https://en.wikipedia.org/wiki/Character_encoding
In linguistics, a grapheme is the smallest functional unit of a writing system.[1] The word grapheme is derived from Ancient Greek γράφω (gráphō) 'write' and the suffix -eme by analogy with phoneme and other names of emic units. The study of graphemes is called graphemics. The concept of graphemes is abstract and similar to the notion in computing of a character. By comparison, a specific shape that represents any particular grapheme in a given typeface is called a glyph.
https://en.wikipedia.org/wiki/Grapheme
Basic Multilingual Plane
The first plane, plane 0, the Basic Multilingual Plane (BMP) contains characters for almost all modern languages, and a large number of symbols. A primary objective for the BMP is to support the unification of prior character sets as well as characters for writing. Most of the assigned code points in the BMP are used to encode Chinese, Japanese, and Korean (CJK) characters.
The High Surrogate (U+D800–U+DBFF) and Low Surrogate (U+DC00–U+DFFF) codes are reserved for encoding non-BMP characters in UTF-16 by using a pair of 16-bit codes: one High Surrogate and one Low Surrogate. A single surrogate code point will never be assigned a character.
65,520 of the 65,536 code points in this plane have been allocated to a Unicode block, leaving just 16 code points in a single unallocated range (2FE0..2FEF).
https://en.wikipedia.org/wiki/Plane_(Unicode)#Basic_Multilingual_Plane
https://en.wikipedia.org/wiki/Universal_Coded_Character_Set
https://en.wikipedia.org/wiki/Brevity_code
Chart of the Morse code 26 letters and 10 numerals[1]
https://en.wikipedia.org/wiki/Morse_code
https://en.wikipedia.org/wiki/Prosigns_for_Morse_code
https://en.wikipedia.org/wiki/Category:Operating_signals
.jpg)
https://en.wikipedia.org/wiki/Morse_code
To increase the efficiency of encoding, Morse code was originally designed so that the length of each symbol is approximately inverse to the frequency of occurrence of the character that it represents in text of the English language. Thus the most common letter in English, the letter E, has the shortest code – a single dit. Because the Morse code elements are specified by proportion rather than specific time durations, the code is usually transmitted at the highest rate that the receiver is capable of decoding. Morse code transmission rate (speed) is specified in groups per minute, commonly referred to as words per minute.[b][7]
Development and history
Pre-Morse telegraphs and codes
Early in the nineteenth century, European experimenters made progress with electrical signaling systems, using a variety of techniques including static electricity and electricity from Voltaic piles producing electrochemical and electromagnetic changes. These experimental designs were precursors to practical telegraphic applications.[14]
_and_Co.,_8_Dey_Street,_NY_-_Bennington_Museum_-_Bennington,_VT_-_DSC08636.JPG)
Following the discovery of electromagnetism by Hans Christian Ørsted in 1820 and the invention of the electromagnet by William Sturgeon in 1824, there were developments in electromagnetic telegraphy in Europe and America. Pulses of electric current were sent along wires to control an electromagnet in the receiving instrument. Many of the earliest telegraph systems used a single-needle system which gave a very simple and robust instrument. However, it was slow, as the receiving operator had to alternate between looking at the needle and writing down the message. In Morse code, a deflection of the needle to the left corresponded to a dit and a deflection to the right to a dah.[15] By making the two clicks sound different with one ivory and one metal stop, the single needle device became an audible instrument, which led in turn to the Double Plate Sounder System.[16]
William Cooke and Charles Wheatstone in Britain developed an electrical telegraph that used electromagnets in its receivers. They obtained an English patent in June 1837 and demonstrated it on the London and Birmingham Railway, making it the first commercial telegraph. Carl Friedrich Gauss and Wilhelm Eduard Weber (1833) as well as Carl August von Steinheil (1837) used codes with varying word lengths for their telegraph systems.[17] In 1841, Cooke and Wheatstone built a telegraph that printed the letters from a wheel of typefaces struck by a hammer.[18]: 79
Samuel Morse and Alfred Vail
The American artist Samuel Morse, the American physicist Joseph Henry, and mechanical engineer Alfred Vail developed an electrical telegraph system. It needed a method to transmit natural language using only electrical pulses and the silence between them. Around 1837, Morse therefore developed an early forerunner to the modern International Morse code.[18]: 79
The Morse system for telegraphy, which was first used in about 1844, was designed to make indentations on a paper tape when electric currents were received. 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, a spring retracted the stylus and that portion of the moving tape remained unmarked. Morse code was developed so that operators could translate the indentations marked on the paper tape into text messages.
In his earliest design for a code, Morse had planned to transmit only numerals, and to use a codebook to look up each word according to the number which had been sent. However, the code was soon expanded by Alfred Vail in 1840 to include letters and special characters, so it could be used more generally. Vail estimated the frequency of use of letters in the English language by counting the movable type he found in the type-cases of a local newspaper in Morristown, New Jersey.[18]: 84 The shorter marks were called "dots" and the longer ones "dashes", and the letters most commonly used were assigned the shortest sequences of dots and dashes. This code, first used in 1844, became known as Morse landline code, American Morse code, or Railroad Morse, until the end of railroad telegraphy in the U.S. in the 1970s.[citation needed]
Operator-led change from graphical to audible code
In the original Morse telegraph system, the receiver's armature made a clicking noise as it moved in and out of position to mark the paper tape. The telegraph operators soon learned that they could translate the clicks directly into dots and dashes, and write these down by hand, thus making the paper tape unnecessary. When Morse code was adapted to radio communication, the dots and dashes were sent as short and long tone 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.[19]
With the advent of tones produced by radiotelegraph receivers, the operators began to vocalize a dot as dit, and a dash as dah, to reflect the sounds of Morse code they heard. To conform to normal sending speed, dits which are not the last element of a code became voiced as di. For example, the letter L is voiced as di dah di dit.[20][21] Morse code was sometimes facetiously known as "iddy-umpty", a dit lampooned as "iddy" and a dah as "umpty", leading to the word "umpteen".[22]
Gerke's refinement of Morse's code
The Morse code, as specified in the current international standard, International Morse Code Recommendation, ITU-R M.1677-1,[1] was derived from a much-improved proposal by Friedrich Gerke in 1848 that became known as the "Hamburg alphabet".
Gerke changed many of the codepoints, in the process doing away with the different length dashes and different inter-element spaces of American Morse, leaving only two coding elements, the dot and the dash. Codes for German umlauted vowels and CH were introduced. Gerke's code was adopted in Germany and Austria 1851.[23]
This finally led to the International Morse code in 1865. The International Morse code adopted most of Gerke's codepoints. The codes for O and P were taken from a code system developed by Steinheil. A new codepoint was added for J since Gerke did not distinguish between I and J. Changes were also made to X, Y, and Z. This left only four codepoints identical to the original Morse code, namely E, H, K and N, and the latter two had their dahs extended to full length. The original American code being compared dates to 1838; the later American code shown in the table was developed in 1844.[17]
Radiotelegraphy and aviation
In the 1890s, Morse code began to be used extensively for early radio communication before it was possible to transmit voice. In the late 19th and early 20th centuries, most high-speed international communication used Morse code on telegraph lines, undersea cables, and radio circuits.
Although previous transmitters were bulky and the spark gap system of transmission was dangerous and difficult to use, there had been some early attempts: In 1910, the U.S. Navy experimented with sending Morse from an airplane.[24] However the first regular aviation radiotelegraphy was on airships, which had space to accommodate the large, heavy radio equipment then in use. The same year, 1910, a radio on the airship America was instrumental in coordinating the rescue of its crew.[25]
During World War I, Zeppelin airships equipped with radio were used for bombing and naval scouting,[26] and ground-based radio direction finders were used for airship navigation.[26] Allied airships and military aircraft also made some use of radiotelegraphy.
However, there was little aeronautical radio in general use during World War I, and in the 1920s, there was no radio system used by such important flights as that of Charles Lindbergh from New York to Paris in 1927. Once he and the Spirit of St. Louis were off the ground, Lindbergh was truly incommunicado and alone. Morse code in aviation began regular use in the mid-1920s. By 1928, when the first airplane flight was made by the Southern Cross from California to Australia, one of its four crewmen was a radio operator who communicated with ground stations via radio telegraph.
Beginning in the 1930s, both civilian and military pilots were required to be able to use Morse code, both for use with early communications systems and for identification of navigational beacons that transmitted continuous two- or three-letter identifiers in Morse code. Aeronautical charts show the identifier of each navigational aid next to its location on the map.
In addition, rapidly moving field armies could not have fought effectively without radiotelegraphy; they moved more quickly than their communications services could put up new telegraph and telephone lines. This was seen especially in the blitzkrieg offensives of the Nazi German Wehrmacht in Poland, Belgium, France (in 1940), the Soviet Union, and in North Africa; by the British Army in North Africa, Italy, and the Netherlands; and by the U.S. Army in France and Belgium (in 1944), and in southern Germany in 1945.
Maritime flash telegraphy and radio telegraphy
Radiotelegraphy using Morse code was vital during World War II, especially in carrying messages between the warships and the naval bases of the belligerents. Long-range ship-to-ship communication was by radio telegraphy, using encrypted messages because the voice radio systems on ships then were quite limited in both their range and their security. Radiotelegraphy was also extensively used by warplanes, especially by long-range patrol planes that were sent out by those navies to scout for enemy warships, cargo ships, and troop ships.
Morse code was used as an international standard for maritime distress until 1999 when it was replaced by the Global Maritime Distress and Safety System. When the French Navy ceased using Morse code on January 31, 1997, the final message transmitted was "Calling all. This is our last cry before our eternal silence."[27]
Demise of commercial telegraphy
In the United States the final commercial Morse code transmission was on July 12, 1999, signing off with Samuel Morse's original 1844 message, WHAT HATH GOD WROUGHT, and the prosign SK ("end of contact").[28]
As of 2015, the United States Air Force still trains ten people a year in Morse.[29]
The United States Coast Guard has ceased all use of Morse code on the radio, and no longer monitors any radio frequencies for Morse code transmissions, including the international medium frequency (MF) distress frequency of 500 kHz.[30] However, the Federal Communications Commission still grants commercial radiotelegraph operator licenses to applicants who pass its code and written tests.[31] Licensees have reactivated the old California coastal Morse station KPH and regularly transmit from the site under either this call sign or as KSM. Similarly, a few U.S. museum ship stations are operated by Morse enthusiasts.[32]
https://en.wikipedia.org/wiki/Morse_code
Wireless telegraphy or radiotelegraphy is transmission of text messages by radio waves, analogous to electrical telegraphy using cables.[1][2] Before about 1910, the term wireless telegraphy was also used for other experimental technologies for transmitting telegraph signals without wires.[3][4] In radiotelegraphy, information is transmitted by pulses of radio waves of two different lengths called "dots" and "dashes", which spell out text messages, usually in Morse code. In a manual system, the sending operator taps on a switch called a telegraph key which turns the transmitter on and off, producing the pulses of radio waves. At the receiver the pulses are audible in the receiver's speaker as beeps, which are translated back to text by an operator who knows Morse code.
Radiotelegraphy was the first means of radio communication. The first practical radio transmitters and receivers invented in 1894–1895 by Guglielmo Marconi used radiotelegraphy. It continued to be the only type of radio transmission during the first few decades of radio, called the "wireless telegraphy era" up until World War I, when the development of amplitude modulation (AM) radiotelephony allowed sound (audio) to be transmitted by radio. Beginning about 1908, powerful transoceanic radiotelegraphy stations transmitted commercial telegram traffic between countries at rates up to 200 words per minute.
Radiotelegraphy was used for long-distance person-to-person commercial, diplomatic, and military text communication throughout the first half of the 20th century. It became a strategically important capability during the two world wars since a nation without long-distance radiotelegraph stations could be isolated from the rest of the world by an enemy cutting its submarine telegraph cables. Radiotelegraphy remains popular in amateur radio. It is also taught by the military for use in emergency communications. However, commercial radiotelegraphy is obsolete.
https://en.wikipedia.org/wiki/Wireless_telegraphy
https://en.wikipedia.org/wiki/Variable-message_sign
https://en.wikipedia.org/wiki/Prosigns_for_Morse_code
https://en.wikipedia.org/wiki/Digital_signature
https://en.wikipedia.org/wiki/Sign_(semiotics)
https://en.wikipedia.org/wiki/Character_encoding
No comments:
Post a Comment