Wireless telegraphy

From Wikipedia, the free encyclopedia

 This article needs additional citations for verification.
Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2006)

The term Wireless Telegraphy is a historic term used today as applied to early radio telegraph communications techniques and practices. Wireless telegraphy originated as a term to describe electrical signaling without the electric wires to connect the end points. The intent was to distinguish it from the conventional electric telegraph signaling of the day that required wire connection between the end points. The term was initially applied to a variety of competing technologies to communicate messages encoded as symbols, without wires around the turn of the twentieth century with radio emerging as the most significant. These other competing wireless telegraphy technologies are interesting, but pale in significance. Wireless telegraphy rapidly came to be synonymous with Morse Code transmitted with electromagnetic waves decades before it came to be associated with the term radio. Wireless telegraphy is used widely today by amateur radio hobbiests where it is commonly referred to as continuous wave (CW) radio telegraphy, or just CW.

Contents

[edit] The beginning of radio communications

The term Wireless Telegraphy came into widespread use around the turn of the previous century when Spark-gap transmitters and privative receivers made it practical to send telegraph messages over great distances, enabling transcontinental and ship-to-shore signalling. Before that time, wireless telegraphy was an obscure experimental term that applied collectively to an assortment of sometimes unrelated signaling schemes. It included such schemes as large mechanical arms for visual signaling and electrical currents through water and dirt.

As far back as Faraday and Hertz in the early 1800s, when it was discovered that radio waves could be used to send telegraph messages. In 1832, James Bowman Lindsay gave a classroom demonstration of UHF wireless telegraphy to his students. By 1854 he was able to demonstrate transmission across the Firth of Tay from Dundee to Woodhaven (now part of Newport-on-Tay), a distance of two miles.[citation needed] Various wireless telegraphy devices started appearing in the 1860s. Heinrich Hertz demonstrated the existence of electromagnetic radiation (radio waves) in a series of experiments in Germany during the 1880s.

In St. Louis, Missouri, Nikola Tesla made the first public demonstration of a modern wireless system in 1893. Addressing the Franklin Institute in Philadelphia and the National Electric Light Association, he described and demonstrated in detail the principles of wireless telegraphy and radio. The apparatus that he used contained all the elements that were incorporated into radio systems before the development of the vacuum tube. This led to work in using radio signals for wireless communication, initially with limited success. Using spark-gap transmitters plus coherer-receivers were tried by many experimenters, but several were unable to achieve transmission ranges of more than a few hundred metres. This was not the case for all researchers in the field of the wireless arts, though.[1][2] By 1897, Guglielmo Marconi conducted a series of demonstrations with an economical radio system for signalling for communications over practical distances. This helped popularize radio communication 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] Prior technologies other than radio

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. 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].[3] Jozef Murgas, the "Radio Priest", contributed a lot of his revolutionary work in the late 1890s and early 1900s to wireless telegraphy.

Earth conductivity transmissions were found to be limited to impractically short distances, as was conduction through water.

[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 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 an on-board telegraph service. (U.S. Patent 465,971 , Means for Transmitting Signals Electrically, 1891). During the Great Blizzard of 1888, this system was used to send and receive wireless messages from trains buried in snowdrifts, perhaps the first successful use of wireless telegraphy to send distress calls. Disabled trains were able to maintain communications via the Edison induction wireless telegraph system.[4]

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] Notes

  1. ^ In the beginning of 1895, Tesla was transmitting to a distance of 50 miles from New York City to West Point. See the PBS website, "Marconi and Tesla: Who invented radio?" (ed. this is noted as having been accomplished in Leland's book concerning Tesla's "Work with Alternating Currents")
  2. ^ Leland I. Anderson, Priority in the Invention of Radio — Tesla vs. Marconi, Antique Wireless Association monograph, 1980, examining the 1943 decision by the US Supreme Court holding the key Marconi patent invalid (9 pages). (21st Century Books)
  3. ^ Fahie, J. J., A History of Wireless Telegraphy, 1838-1899, 1899, p. 29
  4. ^ "Defied the storm's worst-communication always kept up by 'train telegraphy,'" New York Times, March 17, 1888, page 8. Proquest Historical Newspapers (subscription). Retrieved February 6, 2008

[edit] Online resources

[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).