Radio waves range from 300 gigahertz (GHz), or a wavelength of 1 millimeter, to 3 kilohertz (kHz), which corresponds to a wavelength of 100 kilometers. Radio waves are the lowest frequency within the electromagnetic spectrum. The wavelength is the distance from the peak of one wave to the next.
The radio spectrum is typically divided into AM, or amplitude modulation, and FM, frequency modulation. AM waves vary in amplitude but have constant frequency and range from 540 to 1600 kilohertz. FM waves vary in frequency but are constant in amplitude, and range from 88 to 108 megahertz (MHz). Radio waves are not only used in radio transmission, but also in radar, satellite communications, computer networking, television transmission, short wave radio and certain medical procedures, such as magnetic resonance imaging.
Because they are a type of electromagnetic radiation, radio waves travel at the speed of light. The electromagnetic spectrum continues upward after the portion designated as radio waves. The next portion is devoted to microwave radiation, then infrared radiation, then visible light, then ultraviolet radiation and finally X-rays. While the radiation from radio waves is not dangerous to the human body, extremely low frequency radio waves are perceptible to most people. Electromagnetic radiation damage typically begins further up the electromagnetic spectrum, such as with microwave radiation.