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Wireless telegraphy or radiotelegraphy is transmission of text messages by
radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...
s, analogous to electrical telegraphy using
cables Cable may refer to: Mechanical * Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof * Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
. Before about 1910, the term ''wireless telegraphy'' was also used for other experimental technologies for transmitting telegraph signals without wires. In radiotelegraphy, information is transmitted by pulses of radio waves of two different lengths called "dots" and "dashes", which spell out text messages, usually in
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
. In a manual system, the sending operator taps on a switch called a
telegraph key A telegraph key is a specialized electrical switch used by a trained operator to transmit text messages in Morse code in a telegraphy system. Keys are used in all forms of electrical telegraph systems, including landline (also called wir ...
which turns the
transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
on and off, producing the pulses of radio waves. At the receiver the pulses are audible in the receiver's speaker as beeps, which are translated back to text by an operator who knows Morse code. Radiotelegraphy was the first means of radio communication. The first practical radio
transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the ...
s and receivers invented in 1894–1895 by
Guglielmo Marconi Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system. This led to Marconi ...
used radiotelegraphy. It continued to be the only type of radio transmission during the first few decades of radio, called the "wireless telegraphy era" up until
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
, when the development of
amplitude modulation Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In amplitude modulation, the amplitude (signal strength) of the wave is varied in proportion to ...
(AM) radiotelephony allowed sound (
audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of sou ...
) to be transmitted by radio. Beginning about 1908, powerful transoceanic radiotelegraphy stations transmitted commercial telegram traffic between countries at rates up to 200 words per minute. Radiotelegraphy was used for long-distance person-to-person commercial, diplomatic, and military text communication throughout the first half of the 20th century. It became a strategically important capability during the two world wars since a nation without long-distance radiotelegraph stations could be isolated from the rest of the world by an enemy cutting its submarine telegraph cables. Radiotelegraphy remains popular in
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency commu ...
. It is also taught by the military for use in emergency communications. However, commercial radiotelegraphy is obsolete.


Overview

Wireless telegraphy or radiotelegraphy, commonly called CW (
continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...
), ICW (interrupted continuous wave) transmission, or on-off keying, and designated by the
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
as emission type A1A or A2A, is a
radio communication Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300  gigahertz (GHz). They are generated by an electronic device called a trans ...
method. It was transmitted by several different
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
methods during its history. The primitive
spark-gap transmitter A spark-gap transmitter is an obsolete type of transmitter, radio transmitter which generates radio waves by means of an electric spark."Radio Transmitters, Early" in Spark-gap transmitters were the first type of radio transmitter, and were the m ...
s used until 1920 transmitted damped waves, which had very wide bandwidth and tended to interfere with other transmissions. This type of emission was banned by 1934, except for some legacy use on ships.Individual nations enforce this prohibition in their communication laws. In the United States, this is the Federal Communications Commission (FCC) regulations: The
vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied. The type known as ...
(valve) transmitters which came into use after 1920 transmitted code by pulses of unmodulated
sinusoidal A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the '' sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often i ...
carrier wave called
continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...
(CW), which is still used today. To receive CW transmissions, the receiver requires a circuit called a beat frequency oscillator (BFO). The third type of modulation, frequency-shift keying (FSK) was used mainly by radioteletype networks (RTTY). Morse code radiotelegraphy was gradually replaced by radioteletype in most high volume applications by
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. In manual radiotelegraphy the sending operator manipulates a switch called a
telegraph key A telegraph key is a specialized electrical switch used by a trained operator to transmit text messages in Morse code in a telegraphy system. Keys are used in all forms of electrical telegraph systems, including landline (also called wir ...
, which turns the radio transmitter on and off, producing pulses of unmodulated carrier wave of different lengths called "dots" and "dashes", which encode characters of text in
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
. At the receiving location, Morse code is audible in the receiver's earphone or speaker as a sequence of buzzes or beeps, which is translated back to text by an operator who knows Morse code. With automatic radiotelegraphy
teleprinter A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...
s at both ends use a code such as the International Telegraph Alphabet No. 2 and produced typed text. Radiotelegraphy is obsolete in commercial radio communication, and its last civilian use, requiring maritime shipping radio operators to use Morse code for emergency communications, ended in 1999 when the
International Maritime Organization The International Maritime Organization (IMO, French: ''Organisation maritime internationale'') is a specialised agency of the United Nations responsible for regulating shipping. The IMO was established following agreement at a UN conference ...
switched to the satellite-based
GMDSS The Global Maritime Distress and Safety System (GMDSS) is a worldwide system for automated emergency signal communication for ships at sea developed by the United Nations' International Maritime Organization (IMO) as part of the SOLAS Conventio ...
system. However it is still used by
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency commu ...
operators, and military services require signalmen to be trained in Morse code for emergency communication. A CW coastal station, KSM, still exists in California, run primarily as a museum by volunteers, and occasional contacts with ships are made. In a minor legacy use, VHF omnidirectional range (VOR) and NDB radio beacons in the aviation radio navigation service still transmit their one to three letter identifiers in Morse code. Radiotelegraphy is popular amongst
radio amateurs An amateur radio operator is someone who uses equipment at an amateur radio station to engage in two-way personal communications with other amateur operators on radio frequencies assigned to the amateur radio service. Amateur radio operators ha ...
world-wide, who commonly refer to it as
continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...
, or just CW. A 2021 analysis of over 700 million communications logged by the Club Log blog, and a similar review of data logged by the American Radio Relay League, both show that wireless telegraphy is the 2nd most popular mode of
amateur radio Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency commu ...
communication, accounting for nearly 20% of contacts. This makes it more popular than voice communication, but not as popular as the
FT8 FT8 or Franke & Taylor 8 is a frequency shift keying digital mode which was released on June 29, 2017, by the creators Joe Taylor, K1JT and Steve Franke, K9AN along with the software package WSJT.Burmester, Dale March 12, 2019. Amateur Radio Dig ...
digital mode, which accounted for 60% of amateur radio contacts made in 2021. Since 2003, knowledge of Morse code and wireless telegraphy has no longer been required to obtain an amateur radio license in many countries, it is, however, still required in some countries to obtain a licence of a different class. As of 2021, licence Class A in Belarus and Estonia, or the General class in Monaco, or Class 1 in Ukraine require Morse proficiency to access the full amateur radio spectrum including the
high frequency High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten ...
(HF) bands. Further, CEPT Class 1 licence in Ireland, and Class 1 in Russia, both of which require proficiency in wireless telegraphy, offer additional privileges: a shorter and more desirable
call sign In broadcasting and radio communications, a call sign (also known as a call name or call letters—and historically as a call signal—or abbreviated as a call) is a unique identifier for a transmitter station. A call sign can be formally ass ...
in both countries, and the right to use a higher transmit power in Russia.


Non-radio methods

Efforts to find a way to transmit telegraph signals without wires grew out of the success of electric telegraph networks, the first instant telecommunication systems. Developed beginning in the 1830s, a telegraph line was a person-to-person text message system consisting of multiple
telegraph office Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas ...
s linked by an overhead wire supported on telegraph poles. To send a message, an operator at one office would tap on a switch called a
telegraph key A telegraph key is a specialized electrical switch used by a trained operator to transmit text messages in Morse code in a telegraphy system. Keys are used in all forms of electrical telegraph systems, including landline (also called wir ...
, creating pulses of electric current which spelled out a message in
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
. When the key was pressed, it would connect a
battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
to the telegraph line, sending current down the wire. At the receiving office, the current pulses would operate a telegraph sounder, a device that would make a "click" sound when it received each pulse of current. The operator at the receiving station who knew Morse code would translate the clicking sounds to text and write down the message. The
ground Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...
was used as the return path for current in the telegraph circuit, to avoid having to use a second overhead wire. By the 1860s, the telegraph was the standard way to send most urgent commercial, diplomatic and military messages, and industrial nations had built continent-wide telegraph networks, with submarine telegraph cables allowing telegraph messages to bridge oceans. However installing and maintaining a telegraph line linking distant stations was very expensive, and wires could not reach some locations such as ships at sea. Inventors realized if a way could be found to send electrical impulses of Morse code between separate points without a connecting wire, it could revolutionize communications. The successful solution to this problem was the discovery of
radio wave Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (sho ...
s in 1887, and the development of practical radiotelegraphy transmitters and receivers by about 1899, described in the next section. However, this was preceded by a 50-year history of ingenious but ultimately unsuccessful experiments by inventors to achieve wireless telegraphy by other means.


Ground, water, and air conduction

Several wireless electrical signaling schemes based on the (sometimes erroneous) idea that electric currents could be conducted long-range through water, ground, and air were investigated for telegraphy before practical radio systems became available. The original telegraph lines used two wires between the two stations to form a complete electrical circuit or "loop". In 1837, however,
Carl August von Steinheil Carl August von Steinheil (12 October 1801 – 14 September 1870) was a German physicist, inventor, engineer and astronomer. Biography Steinheil was born in Ribeauvillé, Alsace. He studied law in Erlangen since 1821. He then studied astronomy ...
of
Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the third-largest city in Germany, after Berlin and ...
,
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
, found that by connecting one leg of the apparatus at each station to metal plates buried in the ground, he could eliminate one wire and use a single wire for telegraphic communication. This led to speculation that it might be possible to eliminate both wires and therefore transmit telegraph signals through the ground without any wires connecting the stations. Other attempts were made to send the electric current through bodies of water, to span rivers, for example. Prominent experimenters along these lines included Samuel F. B. Morse in the United States and James Bowman Lindsay in Great Britain, who in August 1854, was able to demonstrate transmission across a mill dam at a distance of . US inventors
William Henry Ward William Henry Ward on 30 April 1872 was granted a USA patent for "Improvement for collecting electricity for telegraphing" (). He theorized that an "electrical layer in the atmosphere" could carry signals like a telegraph wire, and thus is sometimes ...
(1871) and Mahlon Loomis (1872) developed electrical conduction systems based on the erroneous belief that there was an electrified atmospheric stratum accessible at low altitude. They thought atmosphere current, connected with a return path using "Earth currents" would allow for wireless telegraphy as well as supply power for the telegraph, doing away with artificial batteries. A more practical demonstration of wireless transmission via conduction came in
Amos Dolbear Amos Emerson Dolbear (November 10, 1837 – February 23, 1910) was an American physicist and inventor. Dolbear researched electrical spark conversion into sound waves and electrical impulses. He was a professor at University of Kentucky in Lex ...
's 1879 magneto electric telephone that used ground conduction to transmit over a distance of a quarter of a mile.Christopher Cooper, The Truth About Tesla: The Myth of the Lone Genius in the History of Innovation, Race Point Publishing, 2015, page 165 In the 1890s inventor
Nikola Tesla Nikola Tesla ( ; ,"Tesla"
''Random House Webster's Unabridged Dictionary''.
; 1856 – 7 January 1943 ...
worked on an air and ground conduction wireless electric power transmission system, similar to Loomis', which he planned to include wireless telegraphy. Tesla's experiments had led him to incorrectly conclude that he could use the entire globe of the Earth to conduct electrical energy and his 1901 large scale application of his ideas, a high-voltage wireless power station, now called
Wardenclyffe Tower Wardenclyffe Tower (1901–1917), also known as the Tesla Tower, was an early experimental wireless transmission station designed and built by Nikola Tesla on Long Island in 1901–1902, located in the village of Shoreham, New York. Tesla inten ...
, lost funding and was abandoned after a few years. Telegraphic communication using earth conductivity was eventually found to be limited to impractically short distances, as was communication conducted through water, or between trenches during World War I.


Electrostatic and electromagnetic induction

Both electrostatic and electromagnetic induction were used to develop wireless telegraph systems that saw limited commercial application. In the United States,
Thomas Edison Thomas Alva Edison (February 11, 1847October 18, 1931) was an American inventor and businessman. He developed many devices in fields such as electric power generation, mass communication, sound recording, and motion pictures. These inventi ...
, in the mid-1880s, patented an electromagnetic induction system he called "grasshopper telegraphy", which allowed telegraphic signals to jump the short distance between a running train and telegraph wires running parallel to the tracks. This system was successful technically but not economically, as there turned out to be little interest by train travelers in the use of an on-board telegraph service. During the
Great Blizzard of 1888 The Great Blizzard of 1888, also known as the Great Blizzard of '88 or the Great White Hurricane (March 11–14, 1888), was one of the most severe recorded blizzards in American history. The storm paralyzed the East Coast from the Chesapeake ...
, this system was used to send and receive wireless messages from trains buried in snowdrifts. The disabled trains were able to maintain communications via their Edison induction wireless telegraph systems, perhaps the first successful use of wireless telegraphy to send distress calls. Edison would also help to patent a ship-to-shore communication system based on electrostatic induction. The most successful creator of an electromagnetic induction telegraph system was William Preece, chief engineer of Post Office Telegraphs of the
General Post Office The General Post Office (GPO) was the state postal system and telecommunications carrier of the United Kingdom until 1969. Before the Acts of Union 1707, it was the postal system of the Kingdom of England, established by Charles II in 1660. ...
(GPO) in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and ...
. Preece first noticed the effect in 1884 when overhead telegraph wires in
Grays Inn Road Gray's Inn Road (or Grays Inn Road) is an important road in the Bloomsbury district of Central London, in the London Borough of Camden. The road begins at the City of London boundary, where it bisects High Holborn, and ends at King's Cross and ...
were accidentally carrying messages sent on buried cables. Tests in Newcastle succeeded in sending a quarter of a mile using parallel rectangles of wire.Kieve, Jeffrey L., ''The Electric Telegraph: A Social and Economic History'', David and Charles, 1973 . In tests across the
Bristol Channel The Bristol Channel ( cy, Môr Hafren, literal translation: "Severn Sea") is a major inlet in the island of Great Britain, separating South Wales from Devon and Somerset in South West England. It extends from the lower estuary of the River Se ...
in 1892, Preece was able to telegraph across gaps of about . However, his induction system required extensive lengths of antenna wires, many kilometers long, at both the sending and receiving ends. The length of those sending and receiving wires needed to be about the same length as the width of the water or land to be spanned. For example, for Preece's station to span the
English Channel The English Channel, "The Sleeve"; nrf, la Maunche, "The Sleeve" ( Cotentinais) or ( Jèrriais), ( Guernésiais), "The Channel"; br, Mor Breizh, "Sea of Brittany"; cy, Môr Udd, "Lord's Sea"; kw, Mor Bretannek, "British Sea"; nl, Het Ka ...
from
Dover, England Dover () is a town and major ferry port in Kent, South East England. It faces France across the Strait of Dover, the narrowest part of the English Channel at from Cap Gris Nez in France. It lies south-east of Canterbury and east of Maidston ...
, to the coast of
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
would require sending and receiving wires of about along the two coasts. These facts made the system impractical on ships, boats, and ordinary islands, which are much smaller than
Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It ...
or
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
. Also, the relatively short distances that a practical Preece system could span meant that it had few advantages over underwater telegraph cables.


Radiotelegraphy

Over several years starting in 1894, the Italian inventor
Guglielmo Marconi Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system. This led to Marconi ...
worked on adapting the newly discovered phenomenon of radio waves to communication, turning what was essentially a laboratory experiment up to that point into a useful communication system, building the first radiotelegraphy system using them. Preece and the GPO in Britain at first supported and gave financial backing to Marconi's experiments conducted on Salisbury Plain from 1896. Preece had become convinced of the idea through his experiments with wireless induction. However, the backing was withdrawn when Marconi formed the Wireless Telegraph & Signal Company. GPO lawyers determined that the system was a telegraph under the meaning of the
Telegraph Act Telegraph Act is a stock short title which used to be used for legislation in the United Kingdom, relating to telegraphy. The Bill for an Act with this short title may have been known as a Telegraph Bill during its passage through Parliament. ...
and thus fell under the Post Office monopoly. This did not seem to hold back Marconi. After Marconi sent wireless telegraphic signals across the Atlantic Ocean in 1901, the system began being used for regular communication including ship-to-shore and ship-to-ship communication. With this development, wireless telegraphy came to mean ''radiotelegraphy'',
Morse code Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one ...
transmitted by radio waves. The first radio transmitters, primitive spark gap transmitters used until World War I, could not transmit voice ( audio signals). Instead, the operator would send the text message on a
telegraph key A telegraph key is a specialized electrical switch used by a trained operator to transmit text messages in Morse code in a telegraphy system. Keys are used in all forms of electrical telegraph systems, including landline (also called wir ...
, which turned the transmitter on and off, producing short ("dot") and long ("dash") pulses of radio waves, groups of which comprised the letters and other symbols of the Morse code. At the receiver, the signals could be heard as musical "beeps" in the earphones by the receiving operator, who would translate the code back into text. By 1910, communication by what had been called "Hertzian waves" was being universally referred to as "
radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30  hertz (Hz) and 300  gigahertz (GHz). They are generated by an electronic device called a tr ...
", and the term wireless telegraphy has been largely replaced by the more modern term "radiotelegraphy".


Continuous wave (CW)

The primitive
spark-gap transmitter A spark-gap transmitter is an obsolete type of transmitter, radio transmitter which generates radio waves by means of an electric spark."Radio Transmitters, Early" in Spark-gap transmitters were the first type of radio transmitter, and were the m ...
s used until 1920 transmitted by a modulation method called damped wave. As long as the telegraph key was pressed, the transmitter would produce a string of transient pulses of radio waves which repeated at an audio rate, usually between 50 and several thousand
hertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that o ...
. In a receiver's earphone, this sounded like a musical tone, rasp or buzz. Thus the Morse code "dots" and "dashes" sounded like beeps. Damped wave had a large frequency bandwidth, meaning that the radio signal was not a single frequency but occupied a wide band of frequencies. Damped wave transmitters had a limited range and interfered with the transmissions of other transmitters on adjacent frequencies. After 1905 new types of radiotelegraph transmitters were invented which transmitted code using a new modulation method:
continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...
(CW) (designated by the
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
as emission type A1A). As long as the telegraph key was pressed, the transmitter produced a continuous sinusoidal wave of constant amplitude. Since all the radio wave's energy was concentrated at a single frequency, CW transmitters could transmit further with a given power, and also caused virtually no interference to transmissions on adjacent frequencies. The first transmitters able to produce continuous wave were the arc converter (Poulsen arc) transmitter, invented by Danish engineer
Valdemar Poulsen Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer who made significant contributions to early radio technology. He developed a magnetic wire recorder called the telegraphone in 1898 and the first continuous wave rad ...
in 1903, and the Alexanderson alternator, invented 1906-1912 by Reginald Fessenden and Ernst Alexanderson. These slowly replaced the spark transmitters in high power radiotelegraphy stations. However, the radio receivers used for damped wave could not receive continuous wave. Because the CW signal produced while the key was pressed was just an unmodulated carrier wave, it made no sound in a receiver's earphones. To receive a CW signal, some way had to be found to make the Morse code carrier wave pulses audible in a receiver. This problem was solved by Reginald Fessenden in 1901. In his "heterodyne" receiver, the incoming radiotelegraph signal is mixed in the receiver's detector crystal or vacuum tube with a constant sine wave generated by an
electronic oscillator An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating ...
in the receiver called a beat frequency oscillator (BFO). The frequency of the oscillator f_\text is offset from the radio transmitter's frequency f_\text. In the detector the two frequencies subtract, and a beat frequency ( heterodyne) at the difference between the two frequencies is produced: f_\text = , f_\text - f_\text, . If the BFO frequency is near enough to the radio station's frequency, the beat frequency is in the audio frequency range and can be heard in the receiver's earphones. During the "dots" and "dashes" of the signal, the beat tone is produced, while between them there is no carrier so no tone is produced. Thus the Morse code is audible as musical "beeps" in the earphones. The BFO was rare until the invention in 1913 of the first practical electronic oscillator, the vacuum tube feedback oscillator by Edwin Armstrong. After this time BFOs were a standard part of radiotelegraphy receivers. Each time the radio was tuned to a different station frequency, the BFO frequency had to be changed also, so the BFO oscillator had to be tunable. In later superheterodyne receivers from the 1930s on, the BFO signal was mixed with the constant
intermediate frequency In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier sig ...
(IF) produced by the superheterodyne's detector. Therefore, the BFO could be a fixed frequency. Continuous-wave vacuum tube transmitters replaced the other types of transmitter with the availability of power tubes after
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
because they were cheap. CW became the standard method of transmitting radiotelegraphy by the 20s, damped wave spark transmitters were banned by 1930 and CW continues to be used today. Even today most communications receivers produced for use in shortwave communication stations have BFOs.


The radiotelegraphy industry

The International Radiotelegraph Union was unofficially established at the first International Radiotelegraph Convention in 1906, and was merged into the
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
in 1932. When the United States entered World War I, private radiotelegraphy stations were prohibited, which put an end to several pioneers' work in this field. By the 1920s, there was a worldwide network of commercial and government radiotelegraphic stations, plus extensive use of radiotelegraphy by ships for both commercial purposes and passenger messages. The transmission of sound ( radiotelephony) began to displace radiotelegraphy by the 1920s for many applications, making possible radio
broadcasting Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began wi ...
. Wireless telegraphy continued to be used for private person-to-person business, governmental, and military communication, such as telegrams and diplomatic communications, and evolved into radioteletype networks. The ultimate implementation of wireless telegraphy was telex, using radio signals, which was developed in the 1930s and was for many years the only reliable form of communication between many distant countries. The most advanced standard,
CCITT The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Comm ...
R.44, automated both routing and encoding of messages by short wave transmissions. Today, due to more modern text transmission methods, Morse code radiotelegraphy for commercial use has become obsolete. On shipboard, the computer and satellite-linked
GMDSS The Global Maritime Distress and Safety System (GMDSS) is a worldwide system for automated emergency signal communication for ships at sea developed by the United Nations' International Maritime Organization (IMO) as part of the SOLAS Conventio ...
system have largely replaced Morse as a means of communication.


Regulation of radiotelegraphy

Continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or partic ...
(CW) radiotelegraphy is regulated by the
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
(ITU) as emission type A1A. The US
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdicti ...
issues a lifetime commercial Radiotelegraph Operator License. This requires passing a simple written test on regulations, a more complex written exam on technology, and demonstrating Morse reception at 20 words per minute plain language and 16 wpm code groups. (Credit is given for amateur extra class licenses earned under the old 20 wpm requirement.)TITLE 47—Telecommunication CHAPTER I—FEDERAL COMMUNICATIONS COMMISSION SUBCHAPTER A—GENERAL PART 13—COMMERCIAL RADIO OPERATORS
/ref>


Gallery

File: Guglielmo Marconi 1901 wireless signal.jpg,
Guglielmo Marconi Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi (; 25 April 187420 July 1937) was an Italian inventor and electrical engineer, known for his creation of a practical radio wave-based wireless telegraph system. This led to Marconi ...
, the father of radio-based wireless telegraphy, in 1901, with one of his first wireless transmitters ''(right)'' and receivers ''(left)'' File: German WW I field telegraph 001.jpg, German troops erecting a wireless field telegraph station during
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
File: German WW I field telegraph 002.jpg, German officers and troops manning a wireless field telegraph station during World War I File:Bildschirmfoto 2019-04-14 um 09.45.16.png, Mobile radio station in German South West Africa, using a hydrogen balloon to lift the antenna


See also

*
AT&T Corporation AT&T Corporation, originally the American Telephone and Telegraph Company, is the subsidiary of AT&T Inc. that provides voice, video, data, and Internet telecommunications and professional services to businesses, consumers, and government agen ...
originally American Telephone and Telegraph Company *
Electrical telegraph Electrical telegraphs were point-to-point text messaging systems, primarily used from the 1840s until the late 20th century. It was the first electrical telecommunications system and the most widely used of a number of early messaging systems ...
* Imperial Wireless Chain


References and notes

; General * American Institute of Electrical Engineers. (1908).
Wireless Telephony – By R. A. Fessenden (Illustrated.)

Transactions of the American Institute of Electrical Engineers
New York: American Institute of Electrical Engineers. ;Citations


Further reading

Listed by date 'latest to earliest'' * Sarkar, T. K., & Baker, D. C. (2006)
History of wireless
Hoboken, NJ: Wiley-Interscience. * Hugh G. J. Aitken, ''Syntony and Spark: The Origins of Radio'', . 1976. * Elliot N. Sivowitch, ''A Technological Survey of Broadcasting’s Pre-History,'' Journal of Broadcasting, 15:1–20 (Winter 1970–71). * Colby, F. M., Williams, T., & Wade, H. T. (1930).
Wireless Telegraphy

The New international encyclopaedia
New York: Dodd, Mead, and Co. *
Wireless telegraphy

The Encyclopædia Britannica
(1922). London: Encyclopædia Britannica. * Stanley, R. (1919)
Text-book on wireless telegraphy
London: Longmans, Green * Miessner, B. F. (1916)
Radiodynamics: The wireless control of torpedoes and other mechanisms
New York: D. Van Nostrand Co * Thompson, S. P. (1915)
Elementary lessons in electricity and magnetism
New York: Macmillan. * Stanley, R. (1914)
Textbook on wireless telegraphy
London: Longmans, Green. * Ashley, C. G., & Hayward, C. B. (1912)
Wireless telegraphy and wireless telephony
an understandable presentation of the science of wireless transmission of intelligence. Chicago: American School of Correspondence. * Massie, W. W., & Underhill, C. R. (1911)
Wireless telegraphy and telephony popularly explained
New York: D. Van Nostrand. * Captain S.S. Robison(1911)
Developments in Wireless Telegraphy
International marine engineering, Volume 16. Simmons-Boardman Pub. Co. * Bottone, S. R. (1910)
Wireless telegraphy and Hertzian waves
London: Whittaker & Co. * Erskine-Murray, J. (1909)
A handbook of wireless telegraphy: its theory and practice, for the use of electrical engineers, students, and operators
New York: Van Nostrand. * Twining, H. L. V., & Dubilier, W. (1909)
Wireless telegraphy and high-frequency electricity; a manual containing detailed information for the construction of transformers, wireless telegraph, and high-frequency apparatus, with chapters on their theory and operation
Los Angeles, Cal: The author.
''The New Physics and Its Evolution''. Chapter VII: A Chapter in the History of Science: Wireless telegraphy
by Lucien Poincaré, eBook #15207, released 2005. riginally, published: New York, D. Appleton, and Company. 1909 * Fleming, J. A. (1908)
The principles of electric wave telegraphy
London: New York and Co. * Simmons, H. H. (1908).
Wireless telegraphy

Outlines of electrical engineering
London: Cassell and Co. * Murray, J. E. (1907)
A handbook of wireless telegraphy
New York: D. Van Nostrand Co.; tc. * Mazzotto, D., & Bottone, S. R. (1906)
Wireless telegraphy and telephony
London: Whittaker & Co. * Collins, A. F. (1905)
Wireless telegraphy; its history, theory, and practice
New York: McGraw Pub. * Sewall, C. H. (1904)
Wireless telegraphy: its origins, development, inventions, and apparatus
New York: D. Van Nostrand. * Trevert, E. (1904)
The A.B.C. of wireless telegraphy; a plain treatise on Hertzian wave signaling; embracing theory, methods of operation, and how to build various pieces of the apparatus employed
Lynn, Mass: Bubier Pub. * Fahie, J. J. (1900)
A history of wireless telegraphy, 1838–1899: including some bare-wire proposals for subaqueous telegraphs
Edinburgh: W. Blackwood and Sons.
Telegraphing across space, Electric wave method
The Electrical engineer. (1884). London: Biggs & Co. * American Institute of Electrical Engineers. (1884)
Transactions of the American Institute of Electrical Engineers
New York: American Institute of Electrical Engineers. ed., Contains ''Radio Telephony'' – By E. B. Craft and E. H. Colpitts (Illustrated)
p. 305


External links

* John Joseph Fahie
''A History of Wireless Telegraphy, 1838–1899: including some bare-wire proposals for subaqueous telegraphs''
1899 (first edition). * John Joseph Fahie
''A History of Wireless Telegraphy: including some bare-wire proposals for subaqueous telegraphs''
1901 (second edition). * John Joseph Fahie

1901 (second edition, in HTML format). *
Alfred Thomas Story Alfred Thomas Story (1842–1934) was an English journalist, poet and author of numerous books. He was born in North Cave, in the county of York, the fourth child in the large family of James Story. His family was an old Durham branch of the No ...
, ''The Story of Wireless Telegraphy'', 190


James Bowman Lindsay
A short biography on his efforts on electric lamps and telegraphy.
Sparks Telegraph Key Review

''Principles of Radiotelegraphy'' (1919)
{{DEFAULTSORT:Wireless Telegraphy Radio Telegraphy Wireless communication systems