Helgert, Hermann J. Department of Electrical and Computer Engineering, George Washington University, Washington, DC.
- Frequency-stability requirements
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A signal-processing technique used in communication systems employing amplitude modulation (AM) of a carrier signal by an information signal. In standard AM systems, varying the amplitude of a sinusoidal carrier in proportion to the amplitude of an information signal results in a frequency translation of the power in the information signal, the extent of which is determined by the frequency of the carrier signal. The resulting power spectrum exhibits power at the frequency of the carrier signal, and upper and lower sidebands of power above and below the carrier frequency. The upper sideband is simply a shift in frequency of the power spectrum of the information signal, with the lower sideband its mirror image. Thus, an information signal m(t) of bandwidth B hertz modulating a carrier of frequency fc hertz produces a distribution of power extending from fc - B hertz to fc+B hertz, and therefore requires a channel of bandwidth of 2B Hertz to convey an information signal of bandwidth B hertz. See also: Amplitude modulation
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