Radio Spectrum

The portion of the continuous range of frequencies of electromagnetic radiation (i.e. oscillating electrical and magnetic energy which travels at the speed of light) used in broadcast transmission. These carrier frequencies, when modulated with a program or information signal, permit the instantaneous transfer of the modulated signal over distances. Reception or demodulation of the transmitted signal by a receiver occurs by separating the information signal from the carrier wave.

The use of modulated carrier waves is constrained by the properties of the carrier frequencies used. Lower frequencies, with longer wavelengths, are generally more suited to long distance transmission, and video signals require more bandwidth than simpler signals.

Since the radio spectrum is limited, an orderly and efficient allocation of this resource is necessary for optimal use and the avoidance of interference between frequencies. Spectrum licensing must consider the propagation characteristics of frequencies as they are affected by geographical and atmospheric conditions, as well as the location, power and directionality of broadcast stations.

See: Frequency, UHF, VHF. Compare: Audio Frequency.

A portion of the electromagnetic spectrum showing the respective frequency bands and wavelengths allocated for communication purposes.