radio
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Radio transmission and reception. The radio frequency oscillator generates rapidly varying electrical signals, which are sent to the transmitting aerial. In the aerial, the signals produce radio waves (the carrier wave), which spread out at the speed of light. The sound signal is added to the carrier wave by the modulator. When the radio waves fall on the receiving aerial, they induce an electrical current in the aerial. The electrical current is sent to the tuning circuit, which picks out the signal from the particular transmitting station desired. The demodulator separates the sound signal from the carrier wave and sends it, after amplification, to the loudspeaker.
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A photograph of the Italian wireless pioneer Guglielmo Marconi beside the telegraph on board his yacht Elettra in the early 1930s. While sailing, Marconi experimented with sending and receiving radio messages.
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The Italian pioneer of radio telegraphy Guglielmo Marconi, speaking from his 700-ton yacht, Elettra in Genoa, Italy, to an audience in Sydney, Australia. The yacht, purchased in 1919, was converted into a floating laboratory where he tested short-wave reception and transmission. By the end of the 1920s he had set up a worldwide system of short-wave stations.
Transmission and reception of radio waves. In radio transmission a microphone converts sound waves (pressure variations in the air) into a varying electric current, which is amplified and used to modulate a carrier wave which is transmitted as electromagnetic waves, which are then picked up by a receiving aerial, amplified, and fed to a loudspeaker, which converts them back into sound waves.
The theory of electromagnetic waves was first developed by Scottish physicist James Clerk Maxwell in 1864, given practical confirmation in the laboratory in 1888 by German physicist Heinrich Hertz, and put to practical use by Italian inventor Guglielmo Marconi, who in 1901 achieved reception of a signal in Newfoundland, Canada, transmitted from Cornwall, England.
To carry the transmitted electrical signal, an oscillator produces a carrier wave of high frequency; different stations are allocated different transmitting carrier frequencies. A modulator superimposes the audio-frequency signal on the carrier. There are two main ways of doing this: amplitude modulation (AM), used for long- and medium-wave broadcasts, in which the strength of the carrier is made to fluctuate in time with the audio signal; and frequency modulation (FM), as used for VHF broadcasts, in which the frequency of the carrier is made to fluctuate. The transmitting aerial emits the modulated electromagnetic waves, which travel outwards from it.
| In radio reception, a receiving aerial picks up minute voltages in response to the waves sent out by a transmitter. A tuned circuit selects a particular frequency, usually by means of a variable capacitor connected across a coil of wire. A demodulator disentangles the audio signal from the carrier, which is now discarded, having served its purpose. An amplifier boosts the audio signal for feeding to the loudspeaker. In a superheterodyne receiver, the incoming signal is mixed with an internally generated signal of fixed frequency so that the amplifier circuits can operate near their optimum frequency. |
radio - events
| 24 December 1906 | USA | Canadian-born US physicist Reginald Fessenden makes the first wireless transmission of speech and music from Brant Rock, Massachusetts using amplitude modification. He broadcasts music, a poem, and a talk, all heard by ships' radio operators. |
| 1907 | USA | Lee De Forest of the De Forest Radio Telephone Co. begins the first regular experimental radio broadcasts in the USA, in New York City. These are for entertainment, and consist mainly of music. |
| 1919 | United Kingdom | The first radio station in Britain is established at Chelmsford, Essex. Using a 6 kW transmitter, two half-hour speech and music programmes are broadcast daily. They are banned the following year for fear of commercialization. |
| 15 January 1920 | United Kingdom | The Marconi Co. begins the first radio broadcast service in Britain. It is suspended later in the year until 1922, as its signal interferes with transport radio communications. |
| 2 November 1920 | USA | The Westinghouse Company establishes the world's first commercial radio station, KDKA, in East Pittsburgh, Pennsylvania, run by the US engineer Frank Conrad, inaugurating national radio broadcasting in the USA. The first broadcast is of the presidential election returns. |
| 1922 | USA | Long-distance telephone lines are used to connect a radio station in New York City with one in Chicago, Illinois, that is broadcasting the action of a football game. It is the beginning of network broadcasting. |
| 26 March 1923 | United Kingdom | The British Broadcasting Company (BBC) begins broadcasting daily weather forecasts in Britain. The first radio play is also transmitted. |
| 1924 | USA | Two million radio sets are in use in the USA. |
| 1926 | United Kingdom | Over 2 million people in Britain hold radio licences. |
| July 1926 | United Kingdom | Following concern about the control of radio in Britain, the British Broadcasting Company (BBC) is incorporated by royal charter (effective from 1 January 1927). As a public body, it is run by a crown-appointed chairman and governors and financed by a licence fee. |
| 7 July 1927 | United Kingdom | The first regular programme of recorded music on the British Broadcasting Corporation (BBC) is broadcast, presented by Christopher Stone, considered to be the world's first disc-jockey. |
| 1930 | United Kingdom | Over 3 million people hold radio licences in Britain. |
| 1933 | US engineer Edwin Armstrong patents frequency modulation (FM) in radio, which eliminates static. | |
| 1937 | USA | In Richmond, Virginia, Irv Abeloff presents the first phone-in radio programme, Telephone Interviews. Radio legislation does not permit callers to appear live, and so all calls are recorded. |
| 1939 | USA | The Radio Corporation of America (RCA) develops the first experimental television sets in the USA. |
| May 1950 | UK | The British Broadcasting Corporation (BBC) radio starts broadcasting The Archers – an everyday story of country people – in the Midland region of England. |
| May 1951 | UK | The British Broadcasting Corporation (BBC) begins radio broadcasts of the comedy show Crazy People, starring Michael Bentine, Spike Milligan, Harry Secombe, and Peter Sellers. In June 1952, it is renamed The Goon Show, which is broadcast until January 1960. |
| April 1961 | UK | The British Broadcasting Corporation (BBC) radio programme Children's Hour stops broadcasting, because it has lost most of its audience to television. |
| 29 March 1964 | UK | Radio Caroline, the first offshore ‘pirate’ radio station broadcasting to Britain, begins transmissions from a ship in the North Sea. Modelled on Radio Luxembourg with its nonstop diet of pop music, it is Britain's first pop music station. |
| 23 November 1964 | UK | Radio Manx becomes the first commercial radio station to broadcast in the UK. |
| 1966 | UK | Annie Nightingale becomes the first female disc jockey on British radio when she appears on British Broadcasting Corporation (BBC) Radio 1. |
| 1967 | UK | The British Broadcasting Corporation (BBC) replaces its Light, Home, and Third Programme radio services with four numbered stations. |
| 15 August 1967 | UK | The British government introduces legislation outlawing pirate radio stations. Radio Caroline continues to broadcast. |
| 30 September 1967 | UK | The British Broadcasting Corporation (BBC) launches a national pop music station, Radio 1. The first programme is The Breakfast Show, presented by Tony Blackburn, and the first record played is ‘Flowers in the Rain’ by the Move. |
| 8 November 1967 | UK | The British Broadcasting Corporation (BBC) launches local radio stations. The first is Radio Leicester. |
| 1 April 1970 | USA | President Richard M Nixon signs a bill banning cigarette advertising on US radio and television. This takes effect the following year. |
| 8 October 1973 | UK | The London Broadcasting Company (LBC) becomes the first commercial radio station in mainland UK, ending the 50-year British Broadcasting Corporation (BBC) monopoly of radio. The first channel, funded by advertising, broadcasts only news. |
| 9 October 1973 | UK | Capital Radio, a pop music radio channel, begins broadcasting as a rival to the British Broadcasting Corporation's (BBC's) Radio 1 in the UK. |
| 9 June 1975 | UK | In Britain, the proceedings of the House of Commons are broadcast live on radio for the first time, by the British Broadcasting Corporation (BBC) and the London Broadcasting Company (LBC). |
| 1976 | USA | The popularity of CB (citizens-band) radio in the USA leads to a record 656,000 licence applications a month; CB code phrases also filter through to everyday life. |
| 30 April 1977 | UK | British Broadcasting Corporation (BBC) Radio 1 and Radio 3 launch quadrophonic broadcasts in Britain. |
| 3 April 1978 | UK | Regular radio broadcasts of the proceedings of the British Parliament begin. |
| April 1993 | UK | Businessman Richard Branson launches Virgin Radio in Britain, a new national rock music station. |
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