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83-534: SOS, when it was first agreed upon by the International Radio Telegraphic Convention in 1906, was merely a distinctive Morse code sequence and was initially not an abbreviation. Later a backronym was created for it in popular usage, and SOS became associated with mnemonic phrases such as "Save Our Souls" and "Save Our Ship". Moreover, due to its high-profile use in emergencies, the phrase "SOS" has entered general usage to informally indicate

166-462: A code became voiced as di . For example, the letter L (   ▄ ▄▄▄ ▄ ▄  ) is voiced as di dah di dit . Morse code was sometimes facetiously known as "iddy-umpty", a dit lampooned as "iddy" and a dah as "umpty", leading to the word " umpteen ". The Morse code, as specified in the current international standard, International Morse Code Recommendation , ITU-R  M.1677-1,

249-578: 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, Q codes , and a set of Morse code abbreviations for typical message components. For example, CQ is broadcast to be interpreted as "seek you" (I'd like to converse with anyone who can hear my signal). The abbreviations OM (old man), YL (young lady), and XYL ("ex-young lady" – wife) are common. YL or OM

332-416: 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;

415-539: 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 . The shorter marks were called "dots" and

498-476: A crisis or the need for action. SOS originated in German government maritime radio regulations adopted effective 1 April 1905. It became a worldwide standard when it was included in the service regulations of the first International Radiotelegraph Convention signed on 3 November 1906, which became effective on 1 July 1908. In modern terminology, SOS is a Morse " procedural signal " or "prosign " , used as

581-455: A distress signal when both operators were off-duty. Eventually, equipment was invented to summon operators by ringing an alarm in the operator's cabin, and on the bridge, and the only switch able to disable the alarm was only permitted to be in the wireless telegraph room. The alarm was sent by the operator on the ship in distress transmitting the radiotelegraph alarm signal (auto-alarm) signal—twelve extra-long dashes, each lasting four seconds with

664-408: A method, an early forerunner to the modern International Morse code. 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

747-569: A one-second gap between them, and transmitted in A2 (modulated CW). The alarm signal was normally sent with a mechanical or electronic timing circuit to ensure it was sent accurately. However, ships radio room clocks typically had markings on the dial to guide operators in sending the signal manually. The regulations for the auto-alarm were defined in the 1927 Safety of Life at Sea (SOLAS) international maritime regulations, and in Article ;19, § 21, of

830-560: A slow data rate) than voice communication (roughly 2,400~2,800 Hz used by SSB voice ). 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

913-483: A start-of-message mark for transmissions requesting assistance when loss of life or catastrophic loss of property is imminent. Other prefixes are used for mechanical breakdowns, requests for medical assistance, and a relayed distress signal originally sent by another station. SOS remained the maritime radio distress signal until 1999, when it was replaced by the Global Maritime Distress and Safety System . SOS

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996-487: 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. To accurately compare code copying speed records of different eras it is useful to keep in mind that different standard words (50 dit durations versus 60 dit durations) and different interword gaps (5 dit durations versus 7 dit durations) may have been used when determining such speed records. For example, speeds run with

1079-404: 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

1162-512: A telegraph that printed the letters from a wheel of typefaces struck by a hammer. The American artist Samuel Morse , the American physicist Joseph Henry , and mechanical engineer Alfred Vail developed an electrical telegraph system. The simple "on or off" nature of its signals made it desirable to find a method of transmitting natural language using only electrical pulses and the silence between them. Around 1837, Morse therefore developed such

1245-446: 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 . The needle clicked each time it moved to the right or left. By making the two clicks sound different (by installing one ivory and one metal stop), transmissions on

1328-434: Is an advantage for visual recognition. Radio (initially known as "wireless telegraphy") was developed in the late 1890s, and was quickly recognized as an important aid to maritime communication. Previously, seagoing vessels had adopted a variety of standardized visual and audio distress signals, using such things as semaphore flags, signal flares, bells, and foghorns. However, cooperation in standardizing radio distress signals

1411-466: 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 , providing the foundation for the modern form of

1494-418: Is followed by a period of signal absence, called a space , equal to the dit duration. The letters of a word are separated by a space of duration equal to three dits , and words are separated by a space equal to seven dits . Morse code can be memorized and sent in a form perceptible to the human senses, e.g. via sound waves or visible light, such that it can be directly interpreted by persons trained in

1577-468: Is formed by a sequence of dits and dahs . The dit duration can vary for signal clarity and operator skill, but for any one message, once established it is the basic unit of time measurement in Morse code. The duration of a dah is three times the duration of a dit (although some telegraphers deliberately exaggerate the length of a dah for clearer signalling). Each dit or dah within an encoded character

1660-560: Is in the polar areas (latitude greater than 70° N or 70° S). The alarm should also activate when the call is received and the distance between the vessel in distress and the receiving vessel cannot be determined. International Radiotelegraph Convention (1906) The first International Radiotelegraph Convention (French: Convention Radiotélégraphique Internationale ) was held in Berlin, Germany, in 1906. It reviewed radio communication (then known as "wireless telegraphy") issues, and

1743-555: Is most popular among amateur radio operators, in the mode commonly referred to as " continuous wave " or "CW". Other, faster keying methods are available in radio telegraphy, such as frequency-shift keying (FSK). 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

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1826-461: Is named after Samuel Morse , one of the early developers of the system adopted for electrical telegraphy . International Morse code encodes the 26  basic Latin letters A to Z , one accented Latin letter ( É ), the Arabic numerals , and a small set of punctuation and procedural signals ( prosigns ). There is no distinction between upper and lower case letters. Each Morse code symbol

1909-434: Is not to be used. In the aviation service, Morse is typically sent at a very slow speed of about 5 words per minute. In the U.S., pilots do not actually have to know Morse to identify the transmitter because the dot/dash sequence is written out next to the transmitter's symbol on aeronautical charts. Some modern navigation receivers automatically translate the code into displayed letters. International Morse code today

1992-476: Is still recognized as a standard distress signal that may be used with any signaling method. It has been used as a visual distress signal, consisting of three short/three long/three short flashes of light, such as from a survival mirror . In some cases the individual letters "S O S" have been spelled out, for example, stamped in a snowbank or formed out of logs on a beach. "S O S" being readable upside down as well as right side up (as an ambigram )

2075-478: Is supposed to have higher readability for both robot and human decoders. Some programs like WinMorse have implemented the standard. 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

2158-416: Is taught "like a language", with each code perceived as a whole "word" instead of a sequence of separate dots and dashes, such as might be shown on a page. 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

2241-413: Is used by an operator when referring to the other operator (regardless of their actual age), and XYL or OM (rather than the expected XYM ) is used by an operator when referring to his or her spouse. QTH is "transmitting location" (spoken "my Q.T.H." is "my location"). The use of abbreviations for common terms permits conversation even when the operators speak different languages. Although

2324-675: The CODEX standard word and the PARIS standard may differ by up to 20%. Today among amateur operators there are several organizations that recognize high-speed code ability, one group consisting of those who can copy Morse at 60  WPM . Also, Certificates of Code Proficiency are issued by several amateur radio societies, including the American Radio Relay League . Their basic award starts at 10  WPM with endorsements as high as 40  WPM , and are available to anyone who can copy

2407-766: 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

2490-578: The Battle of the Atlantic . The signal "SSS" signaled attacked by submarines, while "RRR" warned of an attack by a surface raider, "QQQ" warned of an unknown raider (usually an auxiliary cruiser ), and "AAA" indicated an attack by aircraft. They were usually sent in conjunction with the SOS distress signal. All of these codes later switched from three repeats of the letter to four repeats, e.g., "RRRR". None of these signals

2573-568: The Marconi Company had a policy of refusing to communicate, except in the case of emergency, with stations operated by other companies. There was concern this would result in a Marconi monopoly, that would also give its home country, Great Britain, as much domination in international radio communication as it already held in international undersea telegraph cables. As was the case at the preliminary conference in 1903, Marconi Company officials strongly objected to this interconnection requirement, on

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2656-671: The Marconi International Marine Communication Company issued "Circular 57", which specified that, for the company's worldwide installations, beginning 1 February 1904 "the call to be given by ships in distress or in any way requiring assistance shall be C.Q.D. " An alternative proposal, put forward in 1906 by the U.S. Navy, suggested that the International Code of Signals flag signals should be adopted for radio use, including NC, which stood for "In distress; want immediate assistance". Germany

2739-724: The North Carolina coast. The signal of the Arapahoe was received by the United Wireless Telegraph Company station at Hatteras, North Carolina , and forwarded to the steamer company's offices. However, there was some resistance among Marconi operators to adopting the new signal, and as late as the April ;1912 sinking of the RMS ; Titanic the ship's Marconi operators intermixed CQD and SOS distress calls. In

2822-672: 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. 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

2905-702: The prosign SK ("end of contact"). As of 2015 , the United States Air Force still trains ten people a year in Morse. 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 . However, the Federal Communications Commission still grants commercial radiotelegraph operator licenses to applicants who pass its code and written tests. Licensees have reactivated

2988-420: 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. 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

3071-487: The 1903 conference had been attended by nine nations, the Convention expanded participation to twenty-seven countries. The resulting agreement, signed on November 3, 1906 and scheduled to take effect on July 1, 1908, consisted of four parts: A major area of controversy was a requirement for unlimited access to all "public service" stations, even when the communicating stations were operated by different companies. At this time

3154-698: 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 low , MF high , HF , VHF , and UHF . In some countries, certain portions of the amateur radio bands are reserved for transmission of Morse code signals only. Because Morse code transmissions employ an on-off keyed radio signal, it requires less complex equipment than other radio transmission modes . Morse code also uses less bandwidth (typically only 100–150  Hz wide, although only for

3237-578: The General Regulations annexed to the International Radiotelegraph Convention , 1927.5 5. The Auto Alarm receivers were designed to activate upon receiving four such dashes. Once four valid dashes are detected, the automatic alarm is activated. The distressed ship's operator would then delay sending the SOS message itself to give off-watch radio operators time to reach their radio room. The radiotelephony equivalent of

3320-518: The International code used everywhere else, including all ships at sea and sailing in North American waters. Morse's version became known as American Morse code or railroad code , and is now almost never used, with the possible exception of historical re-enactments. In aviation , pilots use radio navigation aids. To allow pilots to ensure that the stations they intend to use are serviceable,

3403-626: The Second and First are renewed and become this lifetime license. For new applicants, it requires passing a written examination on electronic theory and radiotelegraphy practices, as well as 16  WPM code-group and 20  WPM text tests. However, the code exams are currently waived for holders of Amateur Extra Class licenses who obtained their operating privileges under the old 20  WPM test requirement. Morse codes of one version or another have been in use for more than 160 years — longer than any other electrical message encoding system. What

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3486-539: The United States from the Federal Communications Commission . Demonstration of this ability was still required for the privilege to use the shortwave bands . Until 2000, proficiency at the 20  WPM level was required to receive the highest level of amateur license (Amateur Extra Class); effective April 15, 2000, in the FCC reduced the Extra Class requirement to 5  WPM . Finally, effective on February 23, 2007,

3569-549: The United States through the first part of the twentieth century, three dashes stood for the numeral "5", so in a few cases the distress signal was informally referred to as "S 5 S".) The first ships that have been reported to have transmitted an SOS distress call were the Cunard oceanliner RMS  Slavonia on 10 June 1909 while sailing the Azores , and the steamer SS  Arapahoe on 11 August 1909 while off

3652-530: 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 license requirements. Until 1991, a demonstration of the ability to send and receive Morse code at a minimum of five words per minute ( WPM ) was required to receive an amateur radio license for use in

3735-574: 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 . 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. Following

3818-548: The code. After some minor changes to the letters and a complete revision of the numerals, International Morse Code was standardized by the International Telegraphy Congress in 1865 in Paris, and later became the standard adopted by the International Telecommunication Union (ITU). Morse and Vail's final code specification, however, was only really used only for land-line telegraphy in the United States and Canada, with

3901-456: 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

3984-475: The efficiency of transmission, Morse code was originally designed so that the duration 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,

4067-414: The facility may instead transmit the signal TEST (   ▄▄▄    ▄    ▄ ▄ ▄    ▄▄▄  ), or the identification may be removed, which tells pilots and navigators that the station is unreliable. In Canada, the identification is removed entirely to signify the navigation aid

4150-481: The following signal:   ▄ ▄ ▄ ▄▄▄ ▄▄▄ ▄▄▄ ▄ ▄ ▄  repeated at brief intervals". In both the 1 April 1905 German law and the 1906 international regulations, the distress signal is specified as a continuous Morse code sequence of three dots / three dashes / three dots, with no mention of any alphabetic equivalents. However there

4233-603: The frequently used vowel O . 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 in 1851. 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

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4316-501: The grounds that competing systems were all infringing on Marconi patents, and this also would allow "freeloading" on the extensive network of Marconi coast stations which had been constructed at great expense. The intercommunication issue was directly addressed by Article I of the supplemental protocol: "Each ship station indicated in Article 1 of the Convention shall be bound to intercommunicate with every other ship station without regard to

4399-535: The holder to be chief operator on board a passenger ship. However, since 1999 the use of satellite and very high-frequency maritime communications systems ( GMDSS ) has made them obsolete. (By that point meeting experience requirement for the First was very difficult.) Currently, only one class of license, the Radiotelegraph Operator License, is issued. This is granted either when the tests are passed or as

4482-525: 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),

4565-643: The interests of consistency and maritime safety, the use of CQD appears to have died out thereafter. Additional warning and distress signals followed the introduction of SOS. On 20 January 1914, the London International Convention on Safety of Life at Sea adopted as the "Safety Signal" the Morse code sequence "TTT"   ▄▄▄    ▄▄▄    ▄▄▄  (three "T's" (   ▄▄▄  ))—spaced normally as three letters so as not to be confused with

4648-409: The later American code shown in the table was developed in 1844. 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

4731-443: 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, was what later 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. In the original Morse telegraph system, the receiver's armature made a clicking noise as it moved in and out of position to mark

4814-501: The natural aural selectivity of the human brain, further enhancing weak signal readability. This efficiency makes CW extremely useful for DX (long 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

4897-494: 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. Morse code speed is measured in words per minute ( WPM ) or characters per minute ( CPM ). Characters have differing lengths because they contain differing numbers of dits and dahs . Consequently, words also have different lengths in terms of dot duration, even when they contain

4980-466: The others 16  WPM code group test (five letter blocks sent as simulation of receiving encrypted text) and 20  WPM code text (plain language) test. It was also necessary to pass written tests on operating practice and electronics theory. A unique additional demand for the First Class was a requirement of a year of experience for operators of shipboard and coast stations using Morse. This allowed

5063-408: The paper tape. Early 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. Later telegraphy training found that people become more proficient at receiving Morse code when it

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5146-540: The particular system of radiotelegraphy adopted by these stations respectively.". Because of their close ties with the Marconi interests, six countries, most notably Great Britain and Italy, were unwilling to agree to support this provision. International Morse Code Morse code is a telecommunications method which encodes text characters as standardized sequences of two different signal durations, called dots and dashes , or dits and dahs . Morse code

5229-408: The radiotelegraph alarm signal is the radiotelephony alarm signal, which is the transmission of alternating tones of 2200 Hz and 1300 Hz, with each tone having a duration of 250 ms. Automatic alarm systems aboard ships must activate when such a signal is received and the receiving vessel is within 500 nmi (930 km) of the transmitting vessel's position, or if the distress position

5312-527: The rescue of its crew. During World War I , Zeppelin airships equipped with radio were used for bombing and naval scouting, and ground-based radio direction finders were used for airship navigation. 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

5395-538: The same number of characters. For this reason, some standard word is adopted for measuring operators' transmission speeds: Two such standard words in common use are PARIS and CODEX . Operators skilled in Morse code can often understand ("copy") code in their heads at rates in excess of 40  WPM . In addition to knowing, understanding, and being able to copy the standard written alpha-numeric and punctuation characters or symbols at high speeds, skilled high-speed operators must also be fully knowledgeable of all of

5478-402: The scope of this conference, so no standard signal was adopted at the time, although Article IV of the conference's Final Protocol stated that "Wireless telegraph stations should, unless practically impossible, give priority to calls for help received from ships at sea". Without international regulations, individual organizations were left to develop their practices. On 7 January 1904

5561-826: The single needle device became audible as well as visible, which led in turn to the Double Plate Sounder System. 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. In 1841, Cooke and Wheatstone built

5644-560: The skill. Morse code is usually transmitted by on-off keying of an information-carrying medium such as electric current, radio waves, visible light, or sound waves. The current or wave is present during the time period of the dit or dah and absent during the time between dits and dahs . Since many natural languages use more than the 26 letters of the Latin alphabet , Morse alphabets have been developed for those languages, largely by transliteration of existing codes. To increase

5727-683: The special unwritten Morse code symbols for the standard Prosigns for Morse code and the meanings of these special procedural signals in standard Morse code communications protocol . International contests in code copying are still occasionally held. In July 1939 at a contest in Asheville, North Carolina in the United States, Theodore Roosevelt McElroy ( W1JYN ) set a still-standing record for Morse copying, 75.2  WPM . Pierpont (2004) also notes that 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

5810-535: The stations transmit a 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-DME based at Vilo Acuña Airport in Cayo Largo del Sur, Cuba is identified by " UCL ", and Morse code UCL is repeatedly transmitted on its radio frequency. In some countries, during periods of maintenance,

5893-409: The three dashes of the letter O (   ▄▄▄ ▄▄▄ ▄▄▄  )—and used for messages to ships "involving safety of navigation and being of an urgent character" but short of an emergency. With the development of audio radio transmitters, there was a need for a spoken distress phrase, and " Mayday " (from French m'aider "help me")

5976-469: The traditional telegraph key (straight key) is still used by some amateurs, the use of mechanical semi-automatic keyers (informally called "bugs"), and of fully automatic electronic keyers (called "single paddle" and either "double-paddle" or "iambic" keys) is prevalent today. Software is also frequently employed to produce and decode Morse code radio signals. The ARRL has a readability standard for robot encoders called ARRL Farnsworth spacing that

6059-650: The transmitted text. Members of the Boy Scouts of America may put a Morse interpreter's strip on their uniforms if they meet the standards for translating code at 5  WPM . Through May 2013, the First, Second, and Third Class (commercial) Radiotelegraph Licenses using code tests based upon the CODEX standard word were still being issued in the United States by the Federal Communications Commission. The First Class license required 20  WPM code group and 25  WPM text code proficiency,

6142-481: Was a convention in International Morse whereby three dots comprise the letter "S", and three dashes the letter "O", and it soon became common to informally refer to the distress signal as "S O S", with the 12 January 1907 Electrical World stating that "Vessels in distress use the special signal, SOS, repeated at short intervals." (In American Morse code , which was used by many coastal ships in

6225-541: Was adopted by the 1927 International Radio Convention as the spoken equivalent of SOS. For "TTT", the equivalent spoken signal is " Sécurité " (from French sécurité "safety") for navigational safety, while " Pan-pan " (from French panne "breakdown"; Morse "XXX") signals an urgent but not immediately dangerous situation. French was the international language at the time that these were formalized. During World War II , additional codes were employed to include immediate details about attacks by enemy vessels, especially in

6308-435: 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 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

6391-408: Was derived from a much-improved proposal by Friedrich Gerke in 1848 that became known as the "Hamburg alphabet", its only real defect being the use of an excessively long code (   ▄ ▄▄▄ ▄ ▄ ▄  and later the equal duration code   ▄▄▄ ▄▄▄ ▄▄▄  ) for

6474-559: Was initially limited by national differences and rivalries between competing radio companies. In 1903, an Italian representative at the Berlin Preliminary Conference on Wireless Telegraphy , Captain Quintino Bonomo, discussed the need for common operating procedures, including the suggestion that "ships in distress ... should send the signal SSS DDD at intervals of a few minutes". However, procedural questions were beyond

6557-502: Was initiated by Germany, which three years earlier had hosted a Preliminary Conference on Wireless Telegraphy that called for a subsequent formal conclave to expand on the issues discussed at the original conference. It was initially planned that the Convention would be held in 1904, however a series of events delayed the start by two years. The Convention convened on October 3, 1906, at Berlin, with an overall objective of establishing international standards for radio communication. While

6640-467: 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 call before our eternal silence." 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

6723-635: Was the first country to adopt the SOS distress signal, which it called the Notzeichen signal, as one of three Morse code sequences included in national radio regulations which became effective on 1 April 1905. In 1906, the first International Radiotelegraph Convention met in Berlin, which produced an agreement signed on 3 November 1906 that become effective on 1 July 1908. The convention adopted an extensive collection of Service Regulations, including Article XVI, which read: "Ships in distress shall use

6806-456: Was the first major convention to set international standards for ship-to-shore communication. One notable provision was the adoption of Germany's " SOS " distress signal as an international standard. The resulting agreements were signed on November 3, 1906, and became effective on July 1, 1908. These standards remained in effect until they were updated at the second International Radiotelegraph Convention , held in London in 1912. The Convention

6889-604: Was used on its own. Sending SOS as well as the urgency signal ("XXX" in CW , and "PAN-PAN" in voice) and safety signal ("TTT" in CW, and "SECURITE" in voice) used similar procedures for effectiveness. These were always followed correctly. Ships and coastal stations would normally have required quiet times twice an hour to listen for priority signals, for 3 minutes, at different times for 500 kHz and 2182 kHz . Since many merchant vessels carried only one or two radio operators, no one might hear

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