Morse code

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Chart of the Morse code letters and numerals

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 most natural languages (unlike English) 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 comprises a unique sequence of dots and dashes, with the shorter sequences assigned to the more frequently used letters in English. (The letter 'E' is a single dot; the letter 'T' is 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, though 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 even 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 in existence.

Contents

[hide]

[edit] Development and history

A typical "straight key." This U.S. model, known as the J-38, was manufactured in huge quantities during World War II, and remains in widespread use today. In a straight key, the signal is "on" when the knob is pressed, and "off" when it is released. Length and timing of the dots and dashes are entirely controlled by the operator.

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.[1] To reflect the sound of Morse code, practitioners began to vocalise a dot as "dit", and a dash as "dah". Dots which are not the final element of a character became vocalised as "di"; the letter "C" for instance is vocalised as "dah-di-dah-dit".[2][3]

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 two- or three-letter identifiers in Morse code. Aeronautical charts show the identifier of each navaid next to its location on the map.

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

[edit] Modern International Morse Code

Morse code has been in use for more than 160 years — longer than any other electronic encoding system. What is called Morse code today is actually somewhat different from what was originally developed by Vail and Morse. The Modern International Morse code, or continental code, was created by Friedrich Clemens Gerke in 1848 and initially used for telegraphy between Hamburg and Cuxhaven in Germany. Gerke changed nearly half of the alphabet and all of the figures resulting in substantially the modern form of the code. After some minor changes, in 1865 it was standardised at the International Telegraphy congress in Paris (1865), and later made the norm by the International Telecommunication Union (ITU) as International Morse code. Morse's original code specification, largely limited to use in the United States, became known as American Morse code or "railroad code." American Morse is now very rarely used except in historical re-enactments.

[edit] Aviation

In aviation, instrument pilots use radio navigation aids. To ensure the stations they are using are serviceable they all emit a short set of identification letters (usually a two- to five-letter version of the station name) in Morse code. Station identification letters are shown on air navigation charts. For example the Manchester VOR based at Manchester Airport is cut down to MCT, and Morse code MCT is broadcast on the radio frequency. If a station is unserviceable then it broadcasts TST (for TEST) and tells pilots that the station is unreliable. Like many morse code abbreviations, TST has a particularly noticeable sound—dah di-di-dit dah.

[edit] Amateur radio

Vibroplex semiautomatic key (also called a "bug"). The paddle, when pressed to the right by the thumb, generates a series of dits, the length and timing of which are controlled by a sliding weight toward the rear of the unit. When pressed to the left by the knuckle of the index finger, the paddle generates a dah, the length of which is controlled by the operator. Multiple dahs require multiple presses. Left-handed operators use a key built as a mirror image of this one.

International Morse code today is most popular among amateur radio operators, where it is used as the pattern to key a transmitter on and off in the radio communications mode commonly referred to as "continuous wave" or "CW". The original amateur radio operators used Morse code exclusively, as voice-capable radio transmitters did not become commonly available until around 1920. Until 2003 the International Telecommunication Union (ITU) mandated Morse code proficiency as part of the amateur radio licensing procedure worldwide. However, the World Radiocommunication Conference of 2003 (WRC-03) made the Morse code requirement for amateur radio licensing optional.[4] Many countries subsequently removed the Morse requirement from their licence requirements.[5]

Until 1991, a demonstration of the ability to send and receive Morse code at 5 words per minute (WPM) was required to receive an amateur radio license for use in the United States from the Federal Communications Commission. Demonstration of this ability was still required for the privilege to use the HF bands. Until 2000, proficiency at the 20 WPM level was required to receive the highest level of amateur license (Extra Class); effective April 15, 2000, the FCC reduced the Extra Class requirement to 5 WPM.[6] Finally, effective February 23, 2007, the FCC eliminated the Morse code proficiency requirements for all amateur licenses.

While voice and data transmissions are limited to specific amateur radio bands under U.S. rules, CW is permitted on all amateur bands—LF, MF, HF, UHF, and VHF, with one notable exception being the 60 meter band in the US. In some countries, certain portions of the amateur radio bands are reserved for transmission of Morse code signals only. Because Morse transmissions employ an on-off keyed radio signal, it requires less complex transmission equipment than other forms of radio communication. Morse code also requires less signal bandwidth than voice communication, typically 100–150 Hz, compared to the roughly 2400 Hz used by single-sideband voice, although at a lower data rate. Morse code is received as a high-pitched audio tone, so transmissions are easier to copy than voice through the noise on congested frequencies, and it can be used in very high noise / low signal environments. The fact that the transmitted energy is concentrated into a very limited bandwidth makes it possible to use narrow receiver filters, which suppress or eliminate interference on nearby frequencies. The narrow signal bandwidth also takes advantage of the natural aural selectivity of the human brain, further enhancing weak signal readability. This efficiency makes CW extremely useful for DX (distance) transmissions, as well as for low-power transmissions (commonly called "QRP operation", from the Q-code for "reduce power"). There are several amateur clubs that require solid high speed copy, the highest of these has a standard of 60 WPM. The American Radio Relay League offers a code proficiency certification program that starts at 10 WPM.

The relatively limited speed at which Morse code can be sent led to the development of an extensive number of abbreviations to speed communication. These include prosigns and Q codes, plus a restricted standardized format for typical messages. For example, CQ is broadcast to be interpreted as "seek you" (I'd like to converse with anyone who can hear my signal). OM (old man), YL (young lady) and XYL ("ex YL" - wife) are common pronouns. YL or OM is used by an operator when referring to the other operator, XYL or OM is used by an operator when referring to his or her spouse.

This use of abbreviations for common terms permits conversation even when the operators speak different languages.

Although the traditional telegraph key (straight key) is still used by many amateurs, the use of mechanical semi-automatic keyers (known as "bugs") and of fully-automatic electronic keyers is prevalent today. Computer software is also frequently employed to produce and decode Morse code radio signals.

[edit] Speed records

A commercially manufactured iambic paddle used in conjunction with an electronic keyer to generate high-speed Morse code, the timing of which is controlled by the electronic keyer. Manipulation of dual-lever paddles is similar to the Vibroplex, but pressing the right paddle generates a series of dahs, and squeezing the paddles produces dit-dah-dit-dah sequence. The actions are reversed for left-handed operators.

Operators skilled in Morse code can often understand ("copy") code in their heads at rates in excess of 40 WPM. International contests in code copying are still occasionally held. In July 1939 at a contest in Asheville, NC in the United States Ted R. McElroy set a still-standing record for Morse copying, 75.2 WPM.[7] In his online book on high speed sending, William Pierpont N0HFF notes some operators may have passed 100 WPM. By this time they are "hearing" phrases and sentences rather than words. The fastest speed ever sent by a straight key was achieved in 1942 by Harry Turner W9YZE (d. 1992) who reached 35 WPM in a demonstration at a U.S. Army base.

[edit] Other uses

A U.S. Navy seaman sends Morse code signals in 2005.

As of 2009 commercial radiotelegraph licenses are still being issued in the United States by the Federal Communications Commission. Designed for shipboard and coast station operators, they are awarded to applicants who pass written examinations on advanced radio theory and show 20 WPM code proficiency [this requirement is waived for "old" (20 WPM) Amateur Extra Class licensees]. However, since 1999 the use of satellite and very high frequency maritime communications systems (GMDSS) have essentially made them obsolete.

Radio navigation aids such as VORs and NDBs for aeronautical use broadcast identifying information in the form of Morse Code, though many VOR stations now also provide voice identification.[8]

Military ships, including those of the U.S. Navy, have long used signal lamps to exchange messages in Morse code. Modern use continues, in part, as a way to communicate while maintaining radio silence.

[edit] Applications for the general public

Representation of SOS-Morse code.

An important application is signalling for help through SOS, "· · · — — — · · ·". This can be sent many ways: keying a radio on and off, flashing a mirror, toggling a flashlight and similar methods.

[edit] Morse code as an assistive technology

Morse code has been employed as an assistive technology, helping people with a variety of disabilities to communicate. Morse can be sent by persons with severe motion disabilities, as long as they have some minimal motor control. In some cases this means alternately blowing into and sucking on a plastic tube ("puff and sip" interface). People with severe motion disabilities in addition to sensory disabilities (e.g. people who are also deaf or blind) can receive Morse through a skin buzzer.

In one case reported in the radio amateur magazine QST, an old shipboard radio operator who had a stroke and lost the ability to speak or write was able to communicate with his physician (a radio amateur) by blinking his eyes in Morse. Another example occurred in 1966 when prisoner of war Jeremiah Denton, brought on television by his North Vietnamese captors, Morse-blinked the word TORTURE.

[edit] Representation and timing

This section includes inline links to audio files. If you have trouble playing the files, see Wikipedia Media help.

International Morse code is composed of five elements:

  1. short mark, dot or 'dit' (·) — one unit long
  2. longer mark, dash or 'dah' (–) — three units long
  3. inter-element gap between the dots and dashes within a character — one unit long
  4. short gap (between letters) — three units long
  5. medium gap (between words) — seven units long[9]

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. Strictly speaking it is not binary, as there are five fundamental elements (see quinary). However, this does not mean Morse code cannot be represented as a binary code. In an abstract sense, this is the function that telegraph operators perform when transmitting messages. Working from the above definitions and further defining a 'unit' as a bit, we can visualize any Morse code sequence as a combination of the following five elements:

  1. short mark, dot or 'dit' (·) — 1
  2. longer mark, dash or 'dah' (–) — 111
  3. intra-character gap (between the dots and dashes within a character) — 0
  4. short gap (between letters) — 000
  5. medium gap (between words) — 0000000

Note that this method works only under the assumption that dits and dahs are always separated by gaps, and that gaps are always separated by dits and dahs.

Morse messages are generally transmitted by a hand-operated device such as a telegraph key, so there are variations introduced by the skill of the sender and receiver — more experienced operators can send and receive at faster speeds. In addition, individual operators differ slightly, for example using slightly longer or shorter dashes or gaps, perhaps only for particular characters. This is called their "fist", and receivers can recognize specific individuals by it alone.

The speed of Morse code is measured in wpm or cpm, according to the Paris standard which defines the speed of Morse transmission as the timing needed to send the word "Paris" a given number of times per minute. The word Paris is used because it is representative for a typical text in the English language, and the choice was influenced by the fact that the decision was taken at the International Telegraph Conference in Paris 1865.[citation needed]

Today the length of the reference word is 50 units (including 7 units of word spacing). At the Paris Conference the standard word spacing was specified to be only 5 units,[citation needed] making the total length of the reference word only 48 units, which may be seen in older literature.

The 40 % difference of the two word spacing lengths does have an impact on the evaluation of the results of receiving speed competitions performed at various occasions. X WPM at 5 units word spacing is more difficult to copy than the same text sent at the same nominal speed with 7 units word spacing.

Incidentally the word "Morse" is also 50 units.

The time for one unit can be computed by the formula:

T = 1200 / W

or

T = 6000 / C

Where: T is the unit time in milliseconds, W is the speed in wpm, and C is the speed in cpm.

Below is an illustration of timing conventions. The phrase "MORSE CODE", in Morse code format, would normally be written something like this, where - represents dahs and · represents dits:

-- --- ·-· ··· ·       -·-· --- -·· ·
M   O   R   S  E        C    O   D  E

Next is the exact conventional timing for this phrase, with = representing "signal on", and . representing "signal off", each for the time length of exactly one dit:

         1         2         3         4         5         6         7         8
12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789
 
M------   O----------   R------   S----   E       C----------   O----------   D------   E
===.===...===.===.===...=.===.=...=.=.=...=.......===.=.===.=...===.===.===...===.=.=...=
   ^               ^    ^       ^             ^
   |              dah  dit      |             |
symbol space                letter space    word space

Morse code is often spoken or written with "dah" for dashes, "dit" for dots located at the end of a character, and "di" for dots located at the beginning or internally within the character. Thus, the following Morse code sequence:

M   O   R   S  E          C    O   D  E
-- --- ·-· ··· · (space) -·-· --- -·· ·

is verbally:

Dah-dah dah-dah-dah di-dah-dit di-di-dit dit, Dah-di-dah-dit dah-dah-dah dah-di-dit dit.

Note that there is little point in learning to read written Morse as above; rather, the sounds of all of the letters and symbols need to be learnt, for both sending and receiving.

[edit] Learning Morse Code

People learning Morse code using the Farnsworth method, named for Donald R. "Russ" Farnsworth, also known by his call sign, W6TTB, are taught to send and receive letters and other symbols at their full target speed, that is with normal relative timing of the dots, dashes and spaces within each symbol for that speed. However, initially exaggerated spaces between symbols and words are used, to give "thinking time" to make the sound "shape" of the letters and symbols easier to learn. The spacing can then be reduced with practice and familiarity. Another popular teaching method is the Koch method, named after German psychologist Ludwig Koch, which uses the full target speed from the outset, but begins with just two characters. Once strings containing those two characters can be copied with 90% accuracy, an additional character is added, and so on until the full character set is mastered. In North America, many thousands of individuals have increased their code recognition speed (after initial memorization of the characters) by listening to the regularly scheduled code practice transmissions broadcast by W1AW, the American Radio Relay League's headquarters station. In the United Kingdom many people learnt the morse code by means of a series of words or phrases that have the same rhythm a Morse character. For instance "Q" in Morse is dah - dah - di - dah, which can be memorized by the phrase "God save the Queen"; and the Morse for "F" is di - di - dah - dit, which can be memorized as "Did she like it."

[edit] Letters, numbers, punctuation

Character Code Character Code Character Code Character Code Character Code Character Code
A · — J · — — — S · · · 1 · — — — — Period [.] · — · — · — Colon [:] — — — · · ·
B — · · · K — · — T 2 · · — — — Comma [,] — — · · — — Semicolon [;] — · — · — ·
C — · — · L · — · · U · · — 3 · · · — — Question mark [?] · · — — · · Double dash [=] — · · · —
D — · · M — — V · · · — 4 · · · · — Apostrophe ['] · — — — — · Plus [+] · — · — ·
E · N — · W · — — 5 · · · · · Exclamation mark [!] — · — · — — Hyphen, Minus [-] — · · · · —
F · · — · O — — — X — · · — 6 — · · · · Slash [/], Fraction bar — · · — · Underscore [_] · · — — · —
G — — · P · — — · Y — · — — 7 — — · · · Parenthesis open [(] — · — — · Quotation mark ["] · — · · — ·
H · · · · Q — — · — Z — — · · 8 — — — · · Parenthesis closed [)] — · — — · — Dollar sign [$] · · · — · · —
I · · R · — · 0 — — — — — 9 — — — — · Ampersand [&], Wait · — · · · At sign [@] · — — · — ·

There is no standard representation for the exclamation mark (!), although the KW digraph (— · — · — —) was proposed in the 1980s by the Heathkit Company (a vendor of assembly kits for amateur radio equipment). While Morse code translation software prefers this version, on-air use is not yet universal as some amateur radio operators in Canada and the USA continue to prefer the older MN digraph (— — — ·) carried over from American landline telegraphy code.

The &, $ and the _ signs are not defined inside the ITU recommendation on Morse code. The $ sign code was represented in the Phillips Code, a huge collection of abbreviations used on land line telegraphy, as SX. The representation of the &-sign given above is also the Morse prosign for wait.

On May 24, 2004—the 160th anniversary of the first public Morse telegraph transmission—the Radiocommunication Bureau of the International Telecommunication Union (ITU-R) formally added the @ ("commercial at" or "commat") character to the official Morse character set, using the sequence denoted by the AC digraph (· — — · — ·). This sequence was reportedly chosen to represent "A[T] C[OMMERCIAL]" or a letter "a" inside a swirl represented by a "C".[10] The new character facilitates sending electronic mail addresses by Morse code and is notable since it is the first official addition to the Morse set of characters since World War I.

[edit] Prosigns

Character(s) Code Character(s) Code Character(s) Code
Wait · - · · ·  Error · · · · · · · ·  Understood · · · - · 
Invitation to transmit - · - End of work · · · - · - Starting Signal - · - · -

Defined in the ITU recommendation.

[edit] Non-English extensions to the Morse code

Char. Code Char. Code Char. Code
ä (also æ and ą) · — · — è (also ł) · — · · – ñ (also ń) — — · — —
à (also å) · — — · — é (also đ and ę) · · — · · ö (also ø and ó) — — — ·
ç (also ĉ and ć) — · — · · ĝ — — · — · ŝ · · · — ·
ch (also š) — — — — ĥ — · — — · (Obsolete)
— — — —   (New)
þ ("Thorn") · — — · ·
ð ("Eth") · · — — · ĵ · — — — · ü (also ŭ) · · — —
ś · · · — · · · ź — — · · — · ż — — · · —

[edit] Non-Latin extensions to Morse code

See Other alphabets in Morse code. For Chinese, Chinese telegraph code is used to map Chinese characters to four-digit codes and send these digits out using standard Morse code. For Korean, SKATS maps the hangul through Korean Morse code to the same codes in Morse code and back to their equivalents in the Roman alphabet.

[edit] Alternative display of more common characters for the international code

Some methods of teaching or learning morse code use the dichotomic search table below.

A graphical representation of the dichotomic search table: the user branches left at every dot and right at every dash until the character is finished.
T — M — — O — — — CH — — — —
Ö — — — ·
G — — · Q — — · —
Z — — · ·
N — · K — · — Y — · — —
C — · — ·
D — · · X — · · —
B — · · ·
E · A · — W · — — J · — — —
P · — — ·
R · — · Ä · — · —
L · — · ·
I · · U · · — Ü · · — —
F · · — ·
S · · · V · · · —
H · · · ·

[edit] See also

[edit] References

[edit] External links

Personal tools
Namespaces
Variants
Actions
Navigation
Interaction
Languages