radio frequency, range of electromagnetic waves with a frequency or wavelength suitable for communication uses. Some of these waves serve as carriers of the lower-frequency audio waves; others are modulated by video or digital information. Short waves have relatively high frequencies; long waves have relatively low frequencies. Radio waves are identified by their frequencies, expressed in kilohertz (kHz), i.e., thousands of cycles per second, in megahertz (MHz), i.e., millions of cycles per second, or in gigahertz (GHz), i.e., billions of cycles per seconds. A range, or band, of radio frequencies is assigned to a broadcasting service by the nation in which it operates. In the United States, the Federal Communications Commission is responsible for that task. Signals in the amplitude modulation (AM) broadcast band in the Americas have frequencies ranging from 530 to 1,700 kHz. Frequency modulation (FM) broadcast frequencies in most countries range from approximately 88 MHz to 108 MHz. Other frequencies are assigned to amateur (ham) radio, citizen band (CB) radio, television broadcasting, cellular telephones, global positioning systems, and other uses. Countries cooperate on on a worldwide basis through the International Telecommunication Union, which holds periodic conferences. Radio frequencies are classified as follows:CE5 See also the table entitled Radio Frequencies for the classification of radio frequencies.
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