n.
Electromagnetic radiation of lower frequency (hence longer wavelength) than visible light or infrared radiation , and consisting of the range of frequencies used for navigation signals, AM and FM broadcasting, television transmissions, cell-phone communications, and various forms of radar .
For radio transmission, information is imparted to a carrier wave by varying (modulating) its amplitude, frequency, or duration. The technology of radio arose from the work of Michael Faraday , James Clerk Maxwell , Heinrich Hertz , Guglielmo Marconi , and others, and improvement followed the development of the vacuum tube , the electronic-tube oscillator , the tuned circuit , and other components. Later innovations have included the replacement of tubes by transistors and of wires by printed circuits . See also radio and radar astronomy .