Amplitude modulation

The Audio Signal (top) is transmitted on a carrier wave by modifying the amplitude (middle) or frequency (bottom)

Amplitude modulation (AM) is one of the two ways information is transmitted and received wirelessly using electromagnetic radiation. To transmit data or analog audio, a constant electromagnetic wave (carrier wave) is first produced. Then the amplitude of this wave is modified in a specific pattern which may be translated back into audio or other data at the receiving end. Amplitude modulated signals tent to travel line-of-sight from the source. They also can be interfered with by lightning. For these reasons as well as others, frequency modulation is sometimes a preferred method of communication.