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ssbdemod

Single sideband amplitude demodulation

Syntax

z = ssbdemod(y,Fc,Fs)
z = ssbdemod(y,Fc,Fs,ini_phase)
z = ssbdemod(y,Fc,Fs,ini_phase,num,den)

Description

For All Syntaxes

z = ssbdemod(y,Fc,Fs) demodulates the single sideband amplitude modulated signal y from the carrier signal having frequency Fc (Hz). The carrier signal and y have sampling rate Fs (Hz). The modulated signal has zero initial phase, and can be an upper- or lower-sideband signal. 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 = ssbdemod(y,Fc,Fs,ini_phase) specifies the initial phase of the modulated signal in radians.

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

Examples

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Define the sampling frequency and original signal.

fs = 270000;
t = (0:1/fs:0.01)';
signal = sin(2*pi*300.*t)+2*sin(2*pi*600.*t);

Convert the original signal to upper-sideband and lower-sideband modulated signals using ssbmod. Use a cutoff frequency of 12000 and an initial phase of 0.

fc = 12000;
initialPhase = 0;
lowerSidebandSignal = ssbmod(signal,fc,fs,initialPhase);
upperSidebandSignal = ssbmod(signal,fc,fs,initialPhase,'upper');

Demodulate the lower and upper sideband signals.

s1 = ssbdemod(lowerSidebandSignal,fc,fs);
s2 = ssbdemod(upperSidebandSignal,fc,fs);

Compare processed signals with original and verify reconstruction.

plot(t,signal,'k',t,s1,'r:',t,s2,'g-.');
legend('Original Signal','Demodulation of Lower Sideband','Demodulation of Upper Sideband');

Introduced before R2006a