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Radio Transmission is a generic term applied to wireless electricity, that is electricity transmitted without the use of wires. It was a dream of the pioneers of telegraphy, the first form of communication achieved using electrical means, to dispense with the expensive, time-consuming and unreliable method of installing electrical cables to facilitate communication. The birth of radio transmission to fulfil this need can be traced to early experiments of H. Hertz in 1888 and to James Maxwell\'s electromagnetic theory in 1873 (see electromagnetism).
Hertz had shown that electrical power created in one circuit could be transmitted and detected in a second circuit, although the two circuits were not connected to each other and were indeed separated by a distance of several metres in air. This experiment was used by Hertz to prove some of Maxwell\'s early mathematical theories that had predicted this effect, although Hertz failed to recognize the potential of his work for communication purposes.
The credit for radio transmission for communication belongs in the main to the Italian, G. Marconi. Marconi was inspired by the work Hertz had performed and also had the vision to realize the application of this new technology. At this time, around 1897, other developments in radio came together to form the first practical radiotelegraphy demonstration. An adequate receiver for the early spark-generated radio waves, the coherer, had been discovered by E. Branly, and was demonstrated in lectures by O. Lodge. Lodge had also shown the effects of tuning in radio transmission: that is, making the transmitter and receiver circuits resonate and therefore work at the same frequency. Marconi applied these principles and realized that by using a larger antenna a greater separation distance between transmitter and receiver could be achieved. He succeeded in achieving radio communication over a distance of several miles. In 1900, he successfully used his radiotelegraphy sets to provide ship-to-shore and ship-to-ship communication for the British Admiralty, an obvious use for wireless telegraphy. A few years later he created another milestone in radio transmission by establishing the first radio communication across the Atlantic Ocean.
Further advances in radio transmission followed, for example, speech transmission was greatly helped by the development of early electronic devices. The first diode, invented by T. Edison in 1880, was used in radio receivers from around 1904 and its electronic successor, the triode, was implemented as both an amplifier and oscillator in the transmitter and receiver of electronic radios.
The use of the triode as an oscillator, capable of producing a single high frequency signal, was invaluable in enabling the various modulation schemes devised for radio transmission to be realized. In particular, frequency modulation (or FM as it is better known today), developed in 1933 by E. Armstrong, reduced noise on radio sets and set the standards for transmission quality.
By the 1920s radio broadcasting was under way, for instance from the British Broadcasting Corporation (BBC) in 1927, and radio transmission has since expanded into fields such as radiotelephony, using cellular phones, television broadcasting and the use of radio waves in radar. The radio pioneers\' dream of wireless electricity is today a very well-established and useful reality. AC |
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