range of electromagnetic waves with a frequency or wavelength suitable for utilization in radio communication. 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, i.e., billions of cycles per seconds. Signals in the amplitude modulation (AM) broadcast band have frequencies ranging from 540 to 1,800 kHz. Frequency modulation (FM) broadcast frequencies range from 88 MHz to 108 MHz. A range, or band, of radio frequencies is regularly assigned to a broadcasting station or service by the nation in which it operates. In the United States, the Federal Communications Commission is responsible for that task. Countries cooperate on on a worldwide basis through the International Telecommunications Union, which holds periodic conferences. Radio frequencies are classified as follows:

The Columbia Encyclopedia, Sixth Edition Copyright© 2004, Columbia University Press. Licensed from Lernout & Hauspie Speech Products N.V. All rights reserved.

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