Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio wave. In AM, the amplitude (signal strength) of the wave is varied in proportion to that of the message signal, such as an audio signal. This technique contrasts with angle modulation, in which either the frequency of the carrier wave is varied, as in frequency modulation, or its phase, as in phase modulation.
The equation of an amplitude modulated wave is s(t) = A_c. The modulation index or modulation depth is a measure of how much the amplitude of the carrier wave is varied by the message signal. It is often denoted as a percentage called the percentage of modulation.
Amplitude modulation is used for audio broadcasting on the long, medium, and short wave bands, and for two-way radio communication at VHF for aircraft. It is also used in a variety of other applications, such as the transmission of data in short-range wireless links like Wi-Fi and cellular networks.
