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.

See Also

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