Wireless telegraphy
From Wikipedia, the free encyclopedia
Wireless Telegraphy is electronic signaling, through the ground, bodies of water, or the air, which does not require the direct metallic connection, from transmitter to receiver, that was needed by the original electric telegraphs. The term covers a number of related technologies developed beginning in the mid-1800s, including earth conduction, electrostatic induction, electromagnetic induction, and, most importantly, electromagnetic radiation (radio).
Radio proved to be by far the most efficient of these methods, so, beginning around 1900, most references to "wireless" actually mean radio transmissions, and for those purposes "wireless telegraph" was eventually supplanted by the more precise term "radiotelegraph". But, with the eventual near-disappearance of telegraphic signalling, even this latter term is now very rarely used, although text messaging by mobile telephone can be considered a form of radiotelegraphy.
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[edit] History
The fact that multiple technologies fall under the term "wireless telegraphy" sometimes creates confusion, as it is not always made clear exactly what form of "wireless" technology is being employed. In addition, all the technologies developed for wireless telegraphy would also be adapted for full audio transmissions, or "wireless telephony".
[edit] Ground and water conduction
The first thoughts about wireless telegraph transmissions date back to the earliest days of the electric telegraph. The original telegraphs included both sending and return wires, to provide a complete electrical circuit for the transmission. However, in 1837, Carl August von Steinheil of Munich, Germany found that, by connecting the terminal end of the sending wire to metal plates buried in the ground, the return wire could be eliminated, and only a single wire used for telegraphing. At the time, a common belief was that with this configuration the return current was now traveling through the ground back to the sending point, in order to complete the circuit. This turned out to be incorrect, but it did lead to speculation that it might be possible someday to also eliminate the sending wire, and telegraph through the ground without using any wires at all. Other attempts were made to send through bodies of water, for example, in order to span rivers. Prominent experimenters along these lines included Samuel F. B. Morse in the United States and James Bowman Lindsay in Great Britain — in 1854 Lindsay demonstrated transmission across the Firth of Tay from Dundee to Woodhaven (now part of Newport-on-Tay), a distance of nearly 2 miles [3 kilometers] [1]. However, because of the very high resistance to electrical currents, earth conductivity transmissions were found to be limited to only a few meters, and even the somewhat greater distances possible through water had little practical use.
[edit] Electrostatic Induction and Electromagnetic Induction
Both electrostatic and electromagnetic induction were used to develop wireless telegraph systems which saw limited commercial application. In the United States, Thomas Edison, in the mid-1880s, patented an electrostatic 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 an on-board telegraph service. (U.S. Patent 465971, Means for Transmitting Signals Electrically, 1891).
The most successful creator of an electromagnetic induction system was William Preece in Great Britain. Beginning with tests across the Bristol Channel in 1892, Preece was able to telegraph across gaps of about 5 kilometers. However, his induction system required extensive lengths of wire, many kilometers long, at both the sending and receiving ends, which made it impractical for use on ships or small islands, and the relatively short distances spanned meant it had few advantages over underwater cables.
[edit] Electromagnetic Radiation (Radio)
Heinrich Hertz demonstrated the existence of electromagnetic radiation (radio waves) in a series of groundbreaking experiments in Germany during the 1880s. This led to work in using radio signals for wireless communication, initially with limited success. However, by 1897, Guglielmo Marconi had made a series of demonstrations which showed the practicality of using radio for signalling far greater distances than had been achieved by any other means. This led to an explosion of activity worldwide, which is covered in depth by Invention of Radio and History of Radio.
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 ultimate implementation of wireless telegraphy was telex using radio signals, which was developed in the 1940s, 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. (See telegraphy for more information).
[edit] Notes
- ^ Fahie, J. J., A History of Wireless Telegraphy, 1838-1899, 1899, p. 29
[edit] Online resources
- 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, A History of Wireless Telegraphy: including some bare-wire proposals for subaqueous telegraphs, 1901 (second edition, in HTML format).
- James Bowman Lindsay A short biography on his efforts on electric lamps and telegraphy.
- Sparks Telegraph Key Review
[edit] Further reading
- Hugh G. J. Aitken, Syntony and Spark: the Origins of Radio, ISBN 0-471-01816-3.
- Elliot N. Sivowitch, A Technological Survey of Broadcasting’s Pre-History, Journal of Broadcasting, 15:1-20 (Winter 1970-71).
