Radio aerials sited on the roof of the Science Museum, London, 1980s.

In order to be transmitted, the information in a radio signal is used to modulate a radio-frequency wave. The modulated signal is then amplified, and projected into space by a transmitting antenna. The signals can then be picked up by the aerial of a radio receiver tuned in to the wavelength of the transmision. The first radio signals were succesfully sent by Guglielmo Marconi (1874-1937) in 1894. Marconi devised a means of sending telegraphic mesages, but it was not until 1906 that Reginald Fesenden (1866-1932) developed amplitude modulation, enabling him to make the first sound broadcast. This marked the birth of radio broadcasting as we know it today.