Amplitude Modulation (AM) is the encoding of a carrier wave by variation of its amplitude in accordance with an input signal. Varying the voltage of a carrier or a direct current in order to transmit analog or digital data. AM is the oldest method of transmitting human voice electronically. In an analog telephone conversation, the voice waves on both sides are modulating the voltage of the direct current loop connected to them by the telephone company. Also see Frequency Modulation (FM).
