Wireless telegraphy

Wireless telegraphy or radiotelegraphy, commonly called CW (continuous wave), ICW (interrupted continuous wave) transmission, or on-off keying, and designated by the International Telecommunication Union as emission type A1A or A2A, is a radio communication method. It was transmitted by several different modulation methods during its history. The primitive spark-gap transmitters 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. The vacuum tube (valve) transmitters which came into use after 1920 transmitted code by pulses of unmodulated sinusoidal carrier wave called continuous wave (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. In manual radiotelegraphy the sending operator manipulates a switch called a telegraph key, 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. 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 teleprinters 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 Radiotelegraphy is obsolete in commercial radio communication, and its last civilian use, requiring maritime shipping radio operators to use Morse code for emergency communications, ended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 switched to the satellite-based GMDSS system. However it is still used by amateur radio 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 world-wide, who commonly refer to it as continuous wave, 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 communication, accounting for nearly 20% of contacts. This makes it more popular than voice communication, but not as popular as the FT8 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 (HF) bands. and Class 1 in Russia, ==History==

Landline telegraph networks 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 number of systems using different schemes for transmitting text over wires competed. A Morse telegraph line was a person-to-person text message system consisting of multiple telegraph offices 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, creating pulses of electric current which spelled out a message in Morse code. By the 1860s, the telegraph was the standard way to send most urgent commercial, diplomatic and military messages, 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. Invention of the wireless telegraph From the 1830s inventors had experimented with a series of unsuccessful technologies to transmit wireless telegraphy: magnetic induction systems, ground conduction, conduction through bodies of water, and light beam systems. The successful solution to this problem was the discovery of radio waves in 1887 by Heinrich Hertz, and the development of practical radiotelegraphy transmitters and receivers by about 1899. Over several years starting in 1894, the Italian inventor Guglielmo 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 General Post Office (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 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 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, 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", and the term wireless telegraphy has been largely replaced by the more modern term "radiotelegraphy". == Modulation methods ==

Damped waves The primitive spark-gap transmitters used until the 1920s 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. 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. Continuous waves After 1905 new types of radiotelegraph transmitters were invented which transmitted code using a new modulation method: continuous wave (CW) (designated by the International Telecommunication Union as emission type A1A). As long as the telegraph key was pressed, the transmitter produced a continuous sinusoidal wave of constant amplitude. 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. The beat frequency oscillator (BFO) 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 in the receiver called a beat frequency oscillator (BFO). The frequency of the oscillator f_\text{BFO} is offset from the radio transmitter's frequency f_\text{IN}. In the detector the two frequencies subtract, and a beat frequency (heterodyne) at the difference between the two frequencies is produced: f_\text{BEAT} = |f_\text{IN} - f_\text{BFO}|. 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. Continuous-wave vacuum tube transmitters replaced the other types of transmitter with the availability of power tubes after World War I because they were cheap. CW became the standard method of transmitting radiotelegraphy by the 20s, damped wave spark transmitters were banned by 1930 ==International regulation==

, Germany, 1908. The International Radiotelegraph Union was established at the first International Radiotelegraph Conference in 1906. The path toward international regulation of radiotelegraphy began in 1903, when the German state invited delegates from ten countries to Berlin for a Preliminary Conference on Wireless Telegraphy. This laid the groundwork for the first International Radiotelegraph Convention, signed in Berlin in 1906, which established a Radiotelegraph Union as one of its outcomes. The Union was not an independent international organisation; the term referred to the group of countries that had adhered to the Radiotelegraph Conventions, in the tradition of other unions of the era such as the Postal Union and the Telegraph Union. This development that had been anticipated as early as the 1906 conference, when the French delegate noted that the two would undoubtedly unite in due course. The international collaboration fostered by wireless telegraphy far exceeded the scope of the Radiotelegraph Conventions. The first International Time Conference in Paris in 1912 established a transnational network of wireless stations sending synchronized time beats across continents. Aviation and sea navigation became deeply dependent on the shared wireless infrastructure, creating new international interdependencies in transportation. Already in the 1910s, wireless also began to carry cultural content across borders: concerts and musical performances transmitted through the air reached listeners in multiple countries simultaneously, turning what had begun as a point-to-point communication technology into an early form of international broadcasting. == Amateurs ==

From the end of the nineteenth century, many people experimented with wireless. Some were established professionals in their fields who wanted to apply wireless to their work, such as seismologist Albin Belar from Ljubljana, who used radio time signals to calibrate seismographs and founded the first modern seismological station in Europe, and Father Guido Alfani from Florence, who used wireless time signals from the Eiffel Tower to predict earthquakes. Many hobbyists also built stations from odds and ends in their backyards. From the very beginning of World War I, the European governments had of course to restrict access to wireless. To ensure control of the transmission of messages within a given country, European governments, one by one, issued orders requesting that private stations be dismantled for the war effort, with the main reason to avoid possible disturbances and to prevent messages of national interest from being intercepted by private individuals. In the United States, private radiotelegraphy stations were prohibited in April 1917 when government entered the war. Although it affected several pioneers' work in this field, US radio amateurs generally progressed much more in experiments compared to their European colleagues who experienced the war and restrictions way earlier. Also, there were many amateurs that took risk of experimenting with the technolology illegally. 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. 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 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 system have largely replaced Morse as a means of communication. ==Regulation==

Continuous wave (CW) radiotelegraphy is regulated by the International Telecommunication Union (ITU) as emission type A1A. ==Gallery==

File: Guglielmo Marconi 1901 wireless signal.jpg|Guglielmo Marconi, generally credited as first to develop practical radio-based wireless telegraphy communication, in 1901 with one of his first transmitters (right) and receivers (left) File: KF Braun.png|24 September 1900: Ferdinand Braun and telegraphists at a wireless station in Heligoland. His 2 circuit system made long range radio transmissions possible. File: German WW I field telegraph 001.jpg|German troops erecting a wireless field telegraph station during World War I 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==

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 ==