Radio

Radio is the transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Early speculation that this required a medium of transport, called luminiferous aether, were found to be false. Information is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude or their frequency. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor. This can be detected and transformed into sound or other signals that carry information.

James Clerk Maxwell, a Scottish scientist, developed the theoretical basis for explaining electromagnetism. He predicted that electric and magnetic fields can couple together to form electromagnetic waves. Heinrich Hertz, a German scientist, is credited with being the first to produce and detect such waves at radio frequencies, in 1888, using a sparkgap transmitter in the Ultra High Frequency range.

In 1893, Nikola Tesla, in America, first demonstrated the feasibility of wireless communications. Guglielmo Marconi, an Italian inventor, was one of the first to develop commercial workable radio communication. It is supposed that he sent and received his first radio signal in Italy in 1895.