Editing Demodulation (section)

== AM radio ==
An [[amplitude modulation|AM]] signal encodes the information into the carrier wave by varying its amplitude in direct sympathy with the [[analog signal|analogue signal]] to be sent. There are two methods used to [[Detector (radio)|demodulate AM signals]]:

* The '''[[envelope detector]]''' is a very simple method of demodulation that does not require a [[Coherence (physics)|coherent]] demodulator. It consists of a [[rectifier]] (anything that will pass current in one direction only) or other non-linear component that enhances one half of the received signal over the other and a low-pass filter. The rectifier may be in the form of a single [[diode]] or may be [[Plate detector (radio)|more complex]]. Many natural substances exhibit this rectification behaviour, which is why it was the earliest modulation and demodulation technique used in radio. The filter is usually an [[RC circuit|RC]] [[low-pass filter|low-pass]] type but the filter function can sometimes be achieved by relying on the limited frequency response of the circuitry following the rectifier. The [[crystal radio receiver|crystal set]] exploits the simplicity of AM modulation to produce a receiver with very few parts, using the crystal as the rectifier and the limited frequency response of the headphones as the filter.
* The '''[[product detector]]''' multiplies the incoming signal by the signal of a local oscillator with the same frequency and phase as the carrier of the incoming signal. After filtering, the original audio signal will result.

[[Single-sideband modulation|SSB]] is a form of AM in which the [[suppressed carrier|carrier is reduced or suppressed entirely]], which require coherent demodulation.  For further reading, see [[sideband]].