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This article is about radio, the medium of communication. For other article subjects named radio see radio (disambiguation).

Radio is a technology that allows for the transmission of signals by modulation of electromagnetic waves. These waves travel (propagate) through the air and the vacuum of space equally well, not requiring a medium of transport.

A radio wave is created whenever a charged object accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum. By contrast, other types of emissions which fall outside the RF range are gamma rays, X-rays, infrared & ultraviolet light, and light visible to humans.

When a radio wave passes a wire, it induces a moving electric charge (voltage) that can be transformed into audio or other signals that carry information. Although the word 'radio' is used to describe this phenomenon, the transmissions which we know as television, radio, radar, and cell phone are all in the class of radio frequency emissions.

Table of contents
1 Discovery
2 Invention and history
3 Uses of radio


The theoretical basis of the propagation of electromagnetic waves was first described in 1873 by James Clerk Maxwell in his paper to the Royal Society A dynamical theory of the electromagnetic field, which followed his work between 1861 and 1865.

It was Heinrich Rudolf Hertz who, between 1886 and 1888, first validated Maxwell's theory through experiment, demonstrating that radio radiation had all the properties of waves (now called Hertzian waves), and discovering that the electromagnetic equations could be reformulated into a partial differential equation called the wave equation.

Invention and history

The identity of the original inventor of radio, at the time called wireless telegraphy, is contentious. Claims have been made that Nathan Stubblefield invented radio before either Tesla or Marconi, but his device seems to have worked by induction transmission rather than radio transmission.

In 1893 in St. Louis, Missouri, Nikola Tesla made the first public demonstration of radio communication. Addressing the Franklin Institute in Philadelphia and the National Electric Light Association, he described and demonstrated in detail the principles of radio communication. The apparatus that he used contained all the elements that were incorporated into radio systems before the development of the vacuum tube.

In 1894 British physicist Sir Oliver Lodge demonstrated the possibility of signalling using radio waves using a detecting device called a coherer, a tube filled with iron filings which had been invented by Temistocle Calzecchi-Onesti at Fermo in Italy in 1884. Edouard Branly of France and Alexander Popov of Russia later produced improved versions of the coherer. Popov, who developed a practical communication system based on the coherer, is often considered by his own countrymen to have been the inventor of radio.

In 1896 Guglielmo Marconi was awarded what is sometimes recognised as the world's first patent for radio with British Patent 12039, Improvements in transmitting electrical impulses and signals and in apparatus there-for. In 1897 in the USA, some key developments in radio's early history were created and patented by Nikola Tesla. The US Patent Office reversed its decision in 1904, awarding Guglielmo Marconi a patent for the invention of radio, possibly influenced by Marconi's financial backers in the States, who included Thomas Edison and Andrew Carnegie. In 1909 Marconi, with Karl Ferdinand Braun, was also awarded the Nobel Prize in Physics for "contributions to the development of wireless telegraphy". However, Tesla's patent (number 645576) was reinstated in 1943 by the US Supreme Court, shortly after his death. This decision was based on the fact that there was prior work existing before the establishment of Marconi's patent. Some believe it was apparently made for financal reasons, to allow the US Government to avoid having to the pay damages that were being claimed by the Marconi Company for use of its patents during World War I (ignoring the prior establish work).

Marconi opened the world's first "wireless" factory in Hall Street, Chelmsford, England in 1898, employing around 50 people. Around 1900, Tesla opens the Wardenclyffe Tower facility and advertises services. By 1903, the ariel structure neared completion. Various theories exist on how Tesla intended to achieve the goals of this wireless system (reportedly, a 200 kW system). Wardenclyffe in operation may have allowed secure multichannel transceiving of information and may have allowed universal navigation, time synchronization, and a global location system.

The next great invention was the vacuum tube detector, invented by a team of Westinghouse engineers.

On Christmas Eve, 1906, Reginald Fessenden (using his heterodyne principle) transmitted the first radio audio broadcast in history from Brant Rock Station, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing the song O Holy Night on the violin and reading a passage from the Bible. The world's first regular wireless broadcasts for entertainment commenced in 1922 from the Marconi Research Centre at Writtle near Chelmsford, England, which was also the location of the world's first "wireless" factory.

Early radios ran the entire power of the transmitter through a carbon microphone. In the 1920s, amplifying vacuum tubes revolutionized both radio receivers and radio transmitters.

Developments in the 20th century:

See also history of radio.

Uses of radio

Many of its early uses were naval, for sending Morse code messages between ships and land. Today, radio takes many forms, including wireless networks, mobile communications of all types, as well as radio broadcasting. Read more about radio's history.

Before the advent of television, commercial radio broadcasts included not only news and music, but dramas, comedies, variety shows, and many other forms of entertainment. Radio was unique among dramatic presentation that it used only sound. For more, see radio programming.

There are a number of uses of radio:

See also: Radio propagation and ionosphere, Radio programming, old-time radio, international broadcasting, transistor radio, crystal radio receiver, software radio, Radio hardware, Web radio, types of radio emissions, list of radio stations