amdemod

Amplitude demodulation

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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) returns a demodulated signal z, given the input amplitude modulated (AM) signal y, where the carrier signal has frequency Fc. The carrier signal and y have sampling frequency Fs. The modulated signal y has zero initial phase and zero carrier amplitude, resulting from a suppressed-carrier modulation.

Note

The value of Fs must satisfy Fs ≥ 2Fc.

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 created through transmitted-carrier modulation instead of suppressed-carrier modulation, where 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 Butterworth filter used in the demodulation. The numerator and denominator are generated by [num,den] = butter(n,Fc*2/Fs), where n is the order of the lowpass filter.

example

Examples

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Open Live Script

Set the carrier frequency to 10 kHz and sampling frequency to 80 kHz. Generate a time vector having a duration of 0.01 s.

fc = 10e3;
fs = 80e3;
t = (0:1/fs:0.01)';

Create a two-tone sinusoidal signal with frequencies 300 and 600 Hz.

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.

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

Plot the original and demodulated signals.

plot(t,s,'c',t,z,'b--')
legend('Original Signal','Demodulated Signal')
xlabel('Time (s)')
ylabel('Amplitude')

Plot of the original signal and the demodulated signal. The plot has xlabel Time (s), ylabel Amplitude.

The demodulated signal is nearly identical to the original signal.

Input Arguments

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Amplitude modulated input signal, specified as a scalar, vector, matrix, or 3-D array. Each element of y must be real.

Data Types: double | single

Carrier signal frequency in hertz (Hz), specified as a positive scalar.

Data Types: double

Sampling frequency of the carrier signal and input message signal in hertz (Hz), specified as a positive scalar. To avoid aliasing, the value of Fs must satisfy Fs > 2(Fc + BW), where BW is the bandwidth of the original modulated signal.

Data Types: double

Initial phase of the modulated signal in radians, specified as a scalar.

Data Types: double

Carrier amplitude of the modulated signal, specified as a scalar.

Data Types: double

Lowpass Butterworth filter numerator, specified as a scalar.

Data Types: double

Lowpass Butterworth filter denominator, specified as a scalar.

Data Types: double

Output Arguments

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Amplitude demodulated output signal, returned as a scalar, vector, matrix, or 3-D array.

Version History

Introduced before R2006a

See Also

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