Morse code

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 signals called "dots" and "dashes" respectively, or "dis" and "dahs". Because many non-English natural languages use more than the 26 Roman letters, extensions to the Morse alphabet exist for those languages.

Each character (letter or numeral) is represented by a unique sequence of dots and dashes. The duration of a dash is three times the duration of a dot. Each dot or dash is followed by a short silence, equal to the dot duration. The letters of a word are separated by a space equal to three dots (one dash), and two words are separated by a space equal to seven dots. The dot duration is the basic unit of time measurement in code transmission.

Morse code speed is measured in words per minute (wpm). Characters have differing lengths because they contain differing numbers of dots and dashes. Consequently words also have different lengths in terms of dot duration, even when they contain the same number of characters. For this reason licencing bodies, such as the Federal Communications Commission (FCC) in the US, choose a standard word to measure operator transmission speed. "PARIS" and "CODEX" are two such standard words.

One important feature of Morse code is coding efficiency. The length of each character in Morse is approximately inversely proportional to its frequency of occurrence in English. Thus, the most common letter in English, the letter "E," has the shortest code, a single dot.

A related but different code was originally created for Samuel F. B. Morse's electric telegraph by Alfred Vail in the early 1840s. This code was the forerunner on which modern International Morse code is based. In the 1890s it began to be extensively used for early radio communication before it was possible to transmit voice. In the late nineteenth and early twentieth century, most high-speed international communication used Morse code on telegraph lines, undersea cables and radio circuits.

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. An advantage of Morse code for transmitting over radio waves is that it is able to be received over poor signal conditions that would make voice communications impossible.

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.

Representation of SOS-Morse code.

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. The most common distress signal is SOS or three dots, three dashes and three dots, internationally recognised by treaty.

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, the American artist Samuel F. B. Morse, the American physicist Joseph Henry, and Alfred Vail developed an electrical telegraph system. This system sent pulses of electric current along wires which controlled an electromagnet that was located at the receiving end of the telegraph system.

In 1837, William Cooke and Charles Wheatstone in England began using an electrical telegraph that also used electromagnets in its receivers. However, in contrast with any system of making sounds of clicks, their system used pointing needles that rotated above alphabetical charts to indicate the letters that were being sent. In 1841, Cooke and Wheatstone built a telegraph that printed the letters from a wheel of typefaces struck by a hammer. This machine was based on their 1840 telegraph and worked well; however, they failed to find customers for this system and only two examples were ever built.

On the other hand, the three Americans' 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, 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. Vail determined 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. The shorter marks were called "dots", and the longer ones "dashes", and the letters most commonly used were assigned the shorter sequences of dots and dashes.

Comparison of historical versions of Morse code with the current standard. 1. American Morse code as originally defined. 2. The modified and rationalised version used by Gerke on German railways. 3. The current ITU standard.

In the original Morse telegraphs, 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 it unnecessary to use a paper tape. When Morse code was adapted to radio communication, the dots and dashes were sent as short and long pulses. It was later found that people became 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 sounds of Morse code receivers, the operators 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". For example, the letter "c" was then vocalised as "dah-di-dah-dit".

In aviation, Morse code in radio systems started to be used on a regular basis in the 1920s. Although previous transmitters were bulky and the spark gap system of transmission was difficult to use, there had been some earlier attempts. In 1910 the U.S. Navy experimented with sending Morse from an airplane. That same year a radio on the Airship America had been instrumental in coordinating the rescue of its crew. However, there was no aeronautical radio in 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 alone and incommunicado. On the other hand, when the first airplane flight was made from California to Australia in the 1930s on the Southern Cross (airplane), one of its four crewmen was its 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 identification of navigational beacons which 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.

Radio telegraphy using Morse code was vital during World War II, especially in carrying messages between the warships and the naval bases of the Royal Navy, the Kriegsmarine, the Imperial Japanese Navy, the Royal Canadian Navy, the Royal Australian Navy, the U.S. Navy, and the U.S. Coast Guard. Long-range ship-to-ship communications 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. Radio telegraphy was also extensively used by warplanes, especially by long-range patrol planes that were sent out by these navies to scout for enemy warships, cargo ships, and troop ships.

In addition, rapidly moving armies in the field could not have fought effectively without radio telegraphy, because they moved more rapidly than telegraph and telephone lines could be erected. 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.

Morse code was 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 on January 31, 1997, the final message transmitted was "Calling all. This is our last cry before our eternal silence."

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 CW medium frequency (MF) distress frequency of 500 kHz.

International Morse Code

Morse code has been in use for more than 160 years — longer than any other electrical coding 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 numerals resulting in substantially the modern form of the code. After some minor changes, International Morse Code was standardized at the International Telegraphy Congress in 1865 in Paris, and later International Morse Code made the standard by the International Telecommunication Union (ITU). Morse's original code specification, largely limited to use in the United States and Canada, became known as American Morse code or railroad code. American Morse code is now seldom used except in historical re-enactments.

Aviation

In aviation, instrument pilots use radio navigation aids. To ensure that the stations the pilots are using are serviceable, the stations all transmit 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 VOR based at Manchester Airport in England is abbreviated as "MCT", and MCT in Morse code is transmitted on its radio frequency. In some countries, if a VOR station begins malfunctioning it broadcasts "TST" (for "TEST"), which tells pilots and navigators that the station is unreliable. In Canada, the identification is removed entirely to signify the navigation aid is not to be used.

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" to distinguish it from spark transmissions, not because the transmission was continuous. Other keying methods are available in radio telegraphy, such as frequency shift keying.

The original amateur radio operators used Morse code exclusively, since voice-capable radio transmitters did not become commonly available until around 1920. Until 2003 the International Telecommunication Union mandated Morse code proficiency as part of the amateur radio licensing procedure worldwide. However, the World Radiocommunication Conference of 2003 made the Morse code requirement for amateur radio licensing optional. Many countries subsequently removed the Morse requirement from their licence requirements.

Until 1991, a demonstration of the ability to send and receive Morse code at five words per minute (WPM) based upon the PARIS standard word 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 based upon the PARIS standard word was required to receive the highest level of amateur license (Amateur Extra Class); effective April 15, 2000, the FCC reduced the Extra Class requirement to five WPM. Finally, effective on February 23, 2007, the FCC eliminated the Morse code proficiency requirements from all amateur radio licenses.

While voice and data transmissions are limited to specific amateur radio bands under U.S. rules, Morse code is permitted on all amateur bands—LF, MF, HF, UHF, and VHF, with one notable exception being the 60 meter band in North America. In some countries, certain portions of the amateur radio bands are reserved for transmission of Morse code signals only.

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 abbreviations. 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 some 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.

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. 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. Today among amateur operators there are several organizations that recognize high speed code ability, one recognizing Morse code ability at 60 WPM. Also, Certificates of Code Proficiency are issued by several amateur radio societies, including the American Radio Relay League, whose awards start at 10 WPM and are available to anyone who can copy the transmitted text. To accurately compare code copying speed records of different eras it is useful to keep in mind that different standard words (50 dot durations versus 60 dot durations) and different interword gaps (5 dot durations versus 7 dot durations) may have been used when determining such speed records. For example speeds run with the CODEX standard word and the PARIS standard may differ by up to 20%.

Other uses

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

As of 2010 commercial radiotelegraph licenses using code tests based upon the CODEX standard word are still being issued in the United States by the Federal Communications Commission. Designed for shipboard and coast station operators, licenses are awarded to applicants who pass written examinations on advanced radio theory and show 20 WPM code proficiency [this requirement is currently 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 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. Warships, 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.

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.

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. An original solution to the problem that care takers have to learn to decode has been an electronic typewriter with the codes written on the keys. Codes were sung by users, see the voice typewriter employing morse or votem, Newell and Nabarro, 1968. Morse code can also be translated by computer and used in a speaking communication aid. In some cases this means alternately blowing into and sucking on a plastic tube ("puff and sip" interface). An important advantage of Morse code over row column scanning is that, once learned, it does not require to look at a display. Also, it appears faster than scanning. 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. In these two cases interpreters were available to understand those series of eye-blinks.

Representation, timing and speeds

International Morse code is composed of five elements:

1. short mark, dot or 'dit' (·) — 'dot duration' is 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 dot duration or one unit long
4. short gap (between letters) — three units long
5. 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. 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 assumes that dits and dahs are always separated by dot duration 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 operators can recognize specific individuals by it alone. A good operator who sends clearly and is easy to copy is said to have a "good fist". A "poor fist" is a characteristic of sloppy or hard to copy Morse code.

The measure of the speed of Morse code is wpm, according to either the PARIS standard or alternatively the CODEX standard, which defines the speed of Morse transmission as the timing needed to send either the word "PARIS" or the word "CODEX" a given number of times per minute. The word PARIS was used because it was believed to be representative of a typical text in the English language, and the choice was also influenced by the fact that the decision was taken at the International Telegraph Conference in Paris 1865. The word CODEX was chosen because it was thought to be typical of randomly selected five character code groups. Generally in Morse code measurements 'characters' is meant to include all of the alphabetic 'letters' plus 'numbers' plus 'punctuation marks', and certain so-called 'prosigns'.

In the past, the word PARIS was used to determine the speed of International Morse for amateur radio operator code tests by the United States Federal Communications Commission (FCC) or the FCC Volunteer Examiners. Amateur radio Morse test candidates were tested based upon their ability to simply listen to English plain language messages in code and to later answer multiple choice questions about the content of the message. i.e. 100% accurate copy and recording on paper of the actual characters being sent was not required to pass amateur radio operator Morse tests.

Typically in the United States the word "CODEX" is still used by the FCC for determining the wpm speed of Morse code for commercial radio telegraph operator tests, i.e. for the three classes of radiotelegraph operator licenses. Commercial radiotelegraph candidates are tested on their ability to copy five character randomized code groups by ear while simultaneously recording the characters on paper with 100% accuracy by either manually writing on paper with pencil, or by manually typing on a standard typewriter. Unlike the amateur code tests, perfect recording on paper of all characters sent by code is required by commercial operator Morse code tests.

Measured in dot periods or dot durations, the number of dot durations in the standard word PARIS is 43, while the number of dot durations in the standard word CODEX is 53. Adding the current standard inter-word gap of 7 dot durations to each of these numbers results in a total word length of 50 dot durations (43+7) for PARIS and a total word length of 60 dot durations (53+7) for CODEX. Consequently the ratio of the same wpm code speeds using the two different standard words is 6/5 = 1.2.

Stated in words, CODEX based nominal wpm speeds are 20% (6/5 times) faster than PARIS based nominal wpm speeds.

Thus commercial operators are tested at a wpm speed 20% faster than amateur radio operators were tested at the same 'nominal' wpm speeds. For example the 20 wpm speed test for the FCC T2 commercial operator test was actually 24 wpm as compared to the FCC Amateur Extra Class 20 wpm test speed. Commercial test candidates are required to record 100% accurate copy on paper for at least 1 minute of 5 minutes sent, while the amateur test candidates, copying at a speed 20% slower than commercial operators, were only required to understand 3 minutes of plain English without the requirement for 100% accurate recording of the characters copied. Although many amateur Morse operators exhibit superb code copying abilities, as might be expected from the test requirement differences between commercial and amateur code tests, there is a substantially more difficult level of code copying ability required of commercial operator test candidates than amateur operator test candidates.

In the past the interword gap was not always standardized. Today the length of the reference word PARIS is 50 units (including 7 units of word spacing). At the Paris Conference the standard word spacing was specified to be only 5 units, making the total length of the reference word only 48 units, which may be seen in older literature.

The 40 % difference of the two inter 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.

Based upon a 50 dot duration standard word such as PARIS, the time for one dot duration or one unit can be computed by the formula:

T = 1200 / W

or

T = 6000 / C

Where: T is the unit time or dot duration 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 orally:

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 learned, for both sending and receiving.

Link budget issues

Morse Code cannot be treated as a classical radioteletype (RTTY) signal when it comes to calculating a link margin or a link budget for the simple reason of it possessing variable length dots and dashes as well as variant timing between letters and words. However, because Morse Code when transmitted essentially creates an AM signal (even in on/off keying mode) -- assumptions about signal can be made with respect to similarly timed RTTY signalling.

Because Morse code 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 usually 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 power 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.

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 learned the Morse code by means of a series of words or phrases that have the same rhythm as 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."

A well-known Morse code rhythm from the Second World War period derives from Beethoven's Fifth Symphony, the opening phrase of which was regularly played at the beginning of BBC broadcasts. The timing of the notes corresponds to the Morse for "V"; di - di - di - dah and stood for "V for Victory".

Letters, numbers, punctuation

Character	Code	Character	Code	Character	Code	Character	Code	Character	Code	Character	Code
	· —		· — — —		· · ·		· — — — —	Period [.]	· — · — · —	Colon [:]	— — — · · ·
	— · · ·		— · —		—		· · — — —	Comma [,]	— — · · — —	Semicolon [;]	— · — · — ·
	— · — ·		· — · ·		· · —		· · · — —	Question mark [?]	· · — — · ·	Double dash [=]	— · · · —
	— · ·		— —		· · · —		· · · · —	Apostrophe [']	· — — — — ·	Plus [+]	· — · — ·
	·		— ·		· — —		· · · · ·	Exclamation mark [!]	— · — · — —	Hyphen, Minus [-]	— · · · · —
	· · — ·		— — —		— · · —		— · · · ·	Slash [/], Fraction bar	— · · — ·	Underscore [_]	· · — — · —
	— — ·		· — — ·		— · — —		— — · · ·	Parenthesis open [(]	— · — — ·	Quotation mark ["]	· — · · — ·
	· · · ·		— — · —		— — · ·		— — — · ·	Parenthesis closed [)]	— · — — · —	Dollar sign [$]	· · · — · · —
	· ·		· — ·		— — — — —		— — — — ·	Ampersand [&], Wait	· — · · ·	At sign [@]	· — — · — · (=A+C, see below)

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". 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.

Prosigns

Main article: Prosigns for Morse code

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.

Non-English extensions to the Morse code

Character(s)	Code	Character(s)	Code	Character(s)	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	— — · · —

Non-Latin extensions to Morse code

Main article: 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. Korean Morse code uses the SKATS mapping, originally developed to allow Korean to be typed on western typewriters. SKATS maps hangul characters to arbitrary letters of the Roman alphabet and has no relationship to pronunciation in Korean.

Alternative display of more common characters in International Morse code

See also: Huffman coding

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 · · · ·

See also

• ACP-131
• Chinese telegraph code
• The CW Operators' Club
• Guglielmo Marconi
• High Speed Telegraphy
• Instructograph
• List of international common standards
• Morse code abbreviations
• Morse code mnemonics
• NATO phonetic alphabet
• Radiotelegraphy
• Russian Morse code
• Wabun Code
• Wireless telegraphy

References

• R. W. Burns, Communications: an international history of the formative years, Institution of Electrical Engineers, 2004 ISBN 0863413277.

External links

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