# amdemod

Amplitude demodulation

## Syntax

`z = amdemod(y,Fc,Fs)z = amdemod(y,Fc,Fs,ini_phase)z = amdemod(y,Fc,Fs,ini_phase,carramp)z = amdemod(y,Fc,Fs,ini_phase,carramp,num,den)`

## Description

`z = amdemod(y,Fc,Fs)` demodulates the amplitude modulated signal `y` from a carrier signal with frequency `Fc` (Hz). The carrier signal and `y` have sample frequency `Fs` (Hz). The modulated signal `y` has zero initial phase and zero carrier amplitude, so it represents suppressed carrier modulation. The demodulation process uses the lowpass filter specified by ```[num,den] = butter(5,Fc*2/Fs)```.

 Note:   The `Fc` and `Fs` arguments must satisfy `Fs` > 2(`Fc` + `BW`), where `BW` is the bandwidth of the original signal that was modulated.

`z = amdemod(y,Fc,Fs,ini_phase)` specifies the initial phase of the modulated signal in radians.

`z = amdemod(y,Fc,Fs,ini_phase,carramp)` demodulates a signal that was created via transmitted carrier modulation instead of suppressed carrier modulation. `carramp` is the carrier amplitude of the modulated signal.

`z = amdemod(y,Fc,Fs,ini_phase,carramp,num,den)` specifies the numerator and denominator of the lowpass filter used in the demodulation.

## Examples

The code below illustrates the use of a nondefault filter.

```t = .01; Fc = 10000; Fs = 80000; t = [0:1/Fs:0.01]'; s = sin(2*pi*300*t)+2*sin(2*pi*600*t); % Original signal [num,den] = butter(10,Fc*2/Fs); % Lowpass filter y1 = ammod(s,Fc,Fs); % Modulate. s1 = amdemod(y1,Fc,Fs,0,0,num,den); % Demodulate.```