Wireless telegraphy

Illustration from 1912 of a radiotelegraph operator on a ship sending an emergency SOS call for help

Modern amateur radio operator transmitting Morse code

Wireless telegraphy or radiotelegraphy, commonly called CW (

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.^[10] 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Radiotelegraphy is obsolete in commercial radio communication, and its last civilian use, requiring maritime shipping radio operators to use Morse code for emergency communications, ended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

Efforts to find a way to transmit telegraph signals without wires grew out of the success of

The successful solution to this problem was the discovery of radio waves in 1887, and the development of practical radiotelegraphy transmitters and receivers by about 1899.

Over several years starting in 1894, the Italian inventor

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. 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 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 in the receiver called a beat frequency oscillator (BFO). The frequency of the oscillator ${\displaystyle f_{\text{BFO}}}$ is offset from the radio transmitter's frequency ${\displaystyle f_{\text{IN}}}$. In the detector the two frequencies subtract, and a

) at the difference between the two frequencies is produced: ${\displaystyle f_{\text{BEAT}}=|f_{\text{IN}}-f_{\text{BFO}}|}$. If the BFO frequency is near enough to the radio station's frequency, the beat frequency is in the

The BFO was rare until the invention in 1913 of the first practical electronic oscillator, the vacuum tube feedback

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 and CW continues to be used today. Even today most communications receivers produced for use in shortwave communication stations have BFOs.

Industry

The International Radiotelegraph Union was unofficially established at the

Today, due to more modern text transmission methods, Morse code radiotelegraphy for commercial use has become obsolete. On shipboard, the computer and satellite-linked

Regulation

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

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. (Credit is given for amateur extra class licenses earned under the old 20 wpm requirement.)^[27]

Gallery

• 
  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)
• 
  German troops erecting a wireless field telegraph station during World War I
• 
  German officers and troops manning a wireless field telegraph station during World War I
• 
  Mobile radio station in German South West Africa, using a hydrogen balloon to lift the antenna

See also

• AT&T Corporation originally American Telephone and Telegraph Company
• Electrical telegraph
• Imperial Wireless Chain
• Radioteletype

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

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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,
  ISBN 0471018163
  . 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. [originally, 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.; [etc.].
• 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

Wikimedia Commons has media related to Wireless telegraphy.

Look up wireless telegraphy or radiotelegraphy in Wiktionary, the free dictionary.

Wikisource has original works on the topic: Wireless telegraphy

• John Joseph Fahie, A History of Wireless Telegraphy, 1838–1899: including some bare-wire proposals for subaqueous telegraphs:
  • 1899 (first edition)
  • 1901 (second edition)
• Alfred Thomas Story, The Story of Wireless Telegraphy {1904}
• Sparks Telegraph Key Review
• Cyril M. Jansky, Principles of Radiotelegraphy (1919)
• Principles of Radiotelegraphy (1919)