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Amplitude demodulation


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)


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).


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.


collapse all

Set the sample rate and carrier frequency.

fc = 10e3;
fs = 80e3;

Generate a sinusoidal signal having a 0.01 s duration.

t = [0:1/fs:0.01]';
s = sin(2*pi*300*t)+2*sin(2*pi*600*t);

Create a lowpass filter.

[num,den] = butter(10,fc*2/fs);

Amplitude modulate the signal, s.

y = ammod(s,fc,fs);

Demodulate the received signal.

s1 = amdemod(y,fc,fs,0,0,num,den);

Plot the original and demodulated signals.

legend('Original Signal','Demodulated Signal')
xlabel('Time (s)')

The demodulated signal is nearly identical to the original signal.

Introduced before R2006a