Wireless telegraphy is the transmission of electric telegraphy signals without wires (wirelessly). The term is used synonymously for radio communication systems, also called radiotelegraphy, which transmit telegraph signals by radio waves. When the term originated in the late 19th century it also applied to other types of experimental wireless telegraph communication technologies, such as conduction and induction telegraphy. Radio telegraphy often used manually-sent Morse code; radioteletype (RTTY) always uses mechanically generated and recorded characters.
Wireless telegraphy or radiotelegraph, commonly called CW (continuous wave) telegraphy is a radio transmission system where the operator opens and closes a switch to interrupt a continuously transmitted wave. This results in “dots” and “dashes” that can be used to transmit Morse code.
Although this type of communication has been mostly replaced since its introduction over 100 years ago by other means of communication it is still used by amateur radio operators as well as some military services. A CW coastal station, KSM, still exists in California, run primarily as a museum by volunteers, and occasional contacts with ships are made. Radio beacons, particularly in the aviation service, but also as "placeholders" for commercial ship-to-shore systems, also transmit Morse but at very slow speeds. The US Federal Communications Commission 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. (Cr is given for amateur extra class licenses earned under the old 20 wpm requirement.) Wireless telegraphy is still used widely today by amateur radio hobbyists where it is commonly referred to as radio telegraphy, continuous wave, or just CW. However, its knowledge is not required to obtain any class of amateur license.
This section may stray from the topic of the article. (January 2016)
A number of 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 used two wires between two stations to form a complete electrical circuit or "loop." In 1837, however, Carl August von Steinheil of Munich, Germany, 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, in order 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 500 yards (457 metres).
US inventors William Henry Ward (1871) and Mahlon Loomis (1872) developed an 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's 1879 magneto electric telephone that used ground conduction to transmit over a distance of a quarter of a mile.
In the 1890s inventor Nikola Tesla's 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, 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.
Both electrostatic and electromagnetic induction were used to develop wireless telegraph systems that saw limited commercial application. In the United States, Thomas Edison, 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, 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 in the United Kingdom. Beginning with tests across the Bristol Channel in 1892, Preece was able to telegraph across gaps of about 5 kilometres (3.1 miles). 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 from Dover, England, to the coast of France would require sending and receiving wires of about 30 miles (48 kilometres) along the two coasts. These facts made the system impractical on ships, boats, and ordinary islands, which are much smaller than Great Britain or Greenland. In addition, the relatively short distances that a practical Preece system could span meant that it had few advantages over underwater telegraph cables.
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 wireless telegraphy system using them. 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 comuntication
With this development wireless telegraphy came to mean Morse code transmitted by radio waves. The first radio transmitters, primitive spark gap transmitters used until World War 1, could not transmit voice (audio signals). Instead, the operator would tap out 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".
The International Radiotelegraph Union was unofficially established at first International Radiotelegraph Convention in 1906, and was merged into the International Telecommunication Union 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 wireless telegraphy by the 1920s for many applications, making possible radio broadcasting. 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 has largely replaced Morse as a means of communication.
Guglielmo Marconi, the father of radio based wireless telegraphy, in 1901, with one of his first wireless transmitters (right) and receivers (left)
German troops erecting a wireless field telegraph station during World War I
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