Means of transmitting information by modulating (changing some component of an electromagnetic carrier wave such as the frequency, amplitude, phase, etc. to carry another signal) a pure waveform in which the frequency does not change but the amplitude or maximum distance of the wave’s peaks and troughs from its centerline changes. Amplitude is essentially a measure of how high a wave can go. Think of waves on the ocean. A light surf with one foot tall waves would have a small amplitude while a tidal wave would have a very large amplitude – it is very high from its crest or top to the normal sea level.

Amplitude modulation uses a specific frequency and then modulates or changes that frequency’s amplitude (the maximum height of its waves). These changes in amplitude from one peak to another can be used to transmit another signal. Think of a long row of rolling hills and valleys all the same height and width spaced evenly in the distance. The rolling hills represent the carrier or base frequency before it is modulated or changed. Now, for these hills to carry information, they must be modulated in some way. Applying amplitude modulation will change their heights making some hills higher and some shorter and making some valleys deeper and some more shallow. Now, all the hills and valleys are still the same width and are spaced evenly (their frequency or how often they occur has not changed), but their heights and depths are all different. Now some hills have become narrow mountains while others are low ridges, but they are all the same width spaced evenly. Seeing these hills and valleys, think of a line that seamlessly ran from peak to valley floor to peak to valley floor and so on along the length of the hills. This line following the variety of heights and depths represents a new signal – it is new information derived from the hills and valleys. The new signal is different from the carrier or base signal. This is one way information is carried over air-waves.

Amplitude modulation is the working technique allowing us to receive AM broadcasts on the radio. Tuners receive the signal through an antenna and decode the amplitude modulated carrier or base signal to create a new waveform which can be played back just like how creating a line between the hills and valleys creates a new signal. AM radio signals occupy the electromagnetic frequency band from 530 kHz to 1,750 kHz.