Also known as “AM”, it is a method of adding information to an electronic signal in which the signal is varied by its height to impose information on it. The information being carried causes the amplitude (height of the sine wave) to vary. In the case of LANs, the change in the signal is registered by the receiving device as a 1 or a 0. A combination of these conveys different information, such as letters, numbers, punctuation marks, or control characters. In the world of modems, digital bit stream can be transmitted over an analog network by amplitude modulation, with the carrier frequency being modulated to reflect a 1 bit by a high amplitude sine wave (or series of sine waves) and a 0 bit with a low amplitude sine wave or (series of sine waves). The principal forms of Amplitude Modulation are:
· QDM: Double-band Amplitude Modulation
· QAM: Quadrature Amplitude Modulation
· SSB: Single-sideband Modulation
· VSB: Vestigal Sideband Modulation
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