Frequency band, also called waveband, is a range of radio frequencies usually set aside for a single type of service. A transmitter produces a signal in a band of frequencies around a certain—often constant—carrier frequency. The information being transmitted, such as a sound or a television picture, modulates (changes) the carrier frequency. Because of this modulation, each station must use a range of frequencies for its transmissions. For example, in the United States, most amplitude modulation (AM) radio stations require a frequency band of 5 kilohertz above and below the carrier frequency of their transmitters. One kilohertz equals 1,000 hertz (cycles per second). In Europe and Asia, transmissions on the Global System for Mobile Communications (GSM) cellular-radio system require a frequency band of 100 kilohertz above and below the frequency of the carrier of the transmission. The use of distinct frequency bands keeps nearby stations from interfering with one another’s broadcasts.
Many services are allocated (assigned) their own bands, such as commercial, ship-to-shore, amateur, airplane, satellite, and police broadcasting. In the United States, the Federal Communications Commission (FCC) assigns frequency bands. For example, the frequency band in commercial broadcasting for AM radio stations ranges from 535 to 1,705 kilohertz, and the range for most frequency modulation (FM) radio stations is from 88 to 108 megahertz. One megahertz equals 1 million hertz.
Internationally, the International Telecommunication Union (ITU) regulates frequency band allocations. In most countries, TV stations use several bands in the very high frequency (VHF) and ultrahigh frequency (UHF) ranges. FM stations broadcast in the VHF range, and most current cellular systems worldwide employ the UHF band. Many wireless local area networks (LAN’s) often use bands with carrier frequencies around 2,400 megahertz or 5,000 megahertz. These frequencies are often expressed as 2.4 and 5 gigahertz. One gigahertz equals 1,000 megahertz.
Future ultra wideband (UWB) systems may operate between 3.1 to 10.6 gigahertz. They may be used for several types of applications, such as personal area networks (PAN’s) and other short-range transfers of information. Frequencies from 3 to 30 gigahertz make up the super high frequency (SHF) band.
