The word radio started as a label on telegrams before meaning broadcasts
In December 1904, the British Post Office told telegraph operators to mark messages sent without wires with the word radio. Two years later an international convention in Berlin made that usage official worldwide. Americans kept saying wireless for years, and the newer term only won the public over once broadcasting took off in the 1920s.
The root is the Latin radius, a spoke or ray. In 1881 Alexander Graham Bell, prompted by the French scientist Ernest Mercadier, called his light-beam telephone a radiophone. Édouard Branly named his 1890 wave detector a radio-conducteur, and British engineers wrote of radiotelegraphy by 1898. Wireless telegraphy was too vague, since until about 1910 it also covered systems that sent signals by induction or through water and earth. Lee de Forest pushed the new word in America, founding a radio telephone company in 1907 and warning of radio chaos without strict rules, and the US Navy began favouring it in 1912.
The physics came first. James Clerk Maxwell predicted in 1873 that linked electric and magnetic fields could travel as waves, and that light was such a wave. Heinrich Hertz proved it on 11 November 1886 with a crude spark-gap transmitter. Experiments by Hertz, Jagadish Chandra Bose, Oliver Lodge and others showed these waves reflect, bend and travel at light speed, differing from light only in frequency.
Guglielmo Marconi turned the discovery into a system, sending Morse code more than a kilometre in 1895 and across the Atlantic on 12 December 1901, and he shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun. The first commercial broadcast came on 2 November 1920, when Westinghouse station KDKA in Pittsburgh aired live US presidential election results.
Radio waves span frequencies from 3 hertz to 300 gigahertz, and the International Telecommunication Union divides that spectrum among users. Information rides on them by varying some property of the wave, known as modulation. Beyond broadcasting and phones, radar bounces beams off aircraft and ships to locate them, GPS receivers work out position from the arrival times of signals from beacons at known locations, and garage openers, drones and keyless car entry all run on radio control.
Source: Radio
