Radio is the lowest frequency section of the electromagnetic spectrum, with wavelengths ranging from 1 millimetre to 100 kilometres and frequencies ranging from 300 GHz to 3 kHz. Natural sources such as lightning and celestial occurrences can generate radio waves, as can artificial sources such as broadcast radio towers, cell phones, satellites, and radar.

Radio waves are a form of electromagnetic (EM) radiation with wavelengths longer than infrared light in the electromagnetic spectrum.Radio ways of constant frequency are produced by Oscillators

Radio waves, like all other electromagnetic waves, move at the speed of light. Fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, computer networks, and a variety of other applications all require artificially generated radio waves. Long waves may regularly cover a portion of the Earth, shorter waves can reflect off the ionosphere and travel around the world, and much shorter wavelengths bend or reflect very little and travel on a line of sight.