Amplitude modulation (AM) also referred to as amplitude, by varying the amplitude of the output signal, to achieve the purpose of transmitting information. General changes in the amplitude modulation of the high-frequency end of the output signal and the original signal into a certain function, demodulation end demodulates and outputs the original signal.
In fact, a function is generally proportional relationship. The greatest benefit of this modulation is the modulation and demodulation is very simple, just a diode and a capacitor can, of course, the biggest drawback is the relatively large distortion, while more sensitive to interference, relatively speaking, is a relatively old technology. But technology does not mean that the old applications are not widespread, there are still many areas of application, such as a radio (AM radio) and Aeronautical Radio, Especially in the field of aviation radio, the traveling speed of the aircraft very quickly, quicker fighter, for FM, the Doppler effect is too big, it will affect communications, and AM is not affected by the Doppler effect, it can not be replaced. At the same time there are some improvements AM techniques, such as single sideband modulation (also known as single sideband), residual sideband modulation (Vestigial Side Band, VSB), and amplitude modulation multiple variants such as the current amplitude is widely used in a mobile communication digital modulation.
