## Non-coherent detection

With ASK, the information is conveyed in the amplitude or envelope of the modulated carrier signal and the data can thus be recovered using an envelope detector. The simplest implementation of an envelope detector comprises a diode rectifier and smoothing filter and is classed as a non-coherent detector. The simplicity of this approach is offset by its reduced ability to differentiate the wanted signal from noise when compared with a coherent detector. |
| If quadrature versions of the modulated carrier signal are available in the receiver, that is, a(t) cos wct and a(t) sin wct (where a(t) represents the data imposed amplitude modulation), then an alternative form of envelope detector can be used based on squaring and adding the two quadrature signals and then taking the square root. Mathematically we get: a(t)2 cos2wct + a(t)2 sin2wct = a(t)2 (cos2wct + sin2wct) = a(t)2

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