Radio waves are radiated by electric charges undergoing acceleration. The emission of radio waves is regulated by law, coordinated by an international body called the International Telecommunication Union (ITU), which allocates frequency bands in the radio spectrum for different uses. The first commerical radio broadcast was transmitted on Novemwhen the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA.
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In the mid 1890s, building on techniques physicists were using to study electromagnetic waves, Guglielmo Marconi developed the first apparatus for long-distance radio communication, sending a wireless Morse Code message to a source over a kilometer away in 1895, and the first transatlantic signal on December 12, 1901. The existence of radio waves was first proven by German physicist Heinrich Hertz on November 11, 1886. The noun radio is also used to mean a broadcast radio receiver. In wireless radio remote control devices like drones, garage door openers, and keyless entry systems, radio signals transmitted from a controller device control the actions of a remote device.Īpplications of radio waves that do not involve transmitting the waves significant distances, such as RF heating used in industrial processes and microwave ovens, and medical uses such as diathermy and MRI machines, are not usually called radio. In radio navigation systems such as GPS and VOR, a mobile receiver accepts radio signals from navigational radio beacons whose position is known, and by precisely measuring the arrival time of the radio waves the receiver can calculate its position on Earth. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location.
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In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking, and satellite communication, among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter.
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A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US