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- % 12619250 The Duc Vu & Chun Wa Lee
- clear all;
- close all;
- fs = 500e3;
- Ts = 1/fs;
- N = 50e3;
- t = 0:Ts:(N-1)*Ts;
- fc = 6e3;
- Tg = 1/fc;
- gt = 2+cos(2*pi*fc*t);
- %plot(t, gt)
- % FFT calculation
- [~,G,f] = myfft(gt,fs);
- figure('name','message signal, g(t)')
- plotscript(t,gt,f,G);
- fc1 = 100e3;
- Tc1 = 1/fc1;
- fc1t = 2*cos(2*pi*fc1*t);
- % FFT calculation
- [~,G,f] = myfft(fc1t,fs);
- figure('name','carrier 1 signal, l_1(t)')
- % plot the time domain and frequency domain signals
- plotscript(t,fc1t,f,G);
- %% modulated signal g,AM
- A = 0.5;
- gAM = A*gt.*fc1t;
- % FFT calculation
- [~,G,f] = myfft(gAM,fs);
- figure('name','gAM, g_AM(t)')
- plotscript(t,gAM,f,G);
- %% demodulation
- [b,a] = ellip(5,0.1,50,60000/(fs/2));
- %% scenario 1: l_2(t) = 2*cos(2*pi*fc21*t)
- fc21 = 100e3;
- Tc21 = 1/fc21;
- fc21t = 2*cos(2*pi*fc21*t);
- A = 0.5;
- gdemod = A*gAM.*fc21t;
- gdemod = 2*filter(b,a,gdemod);
- % compute FFT, take the RMS amplitude and frequency vector
- [~,G,f] = myfft(gdemod,fs);
- figure('name','Demodulated Signal, scenario 1')
- % plot the time domain and frequency domain signals
- plotscript(t,gdemod,f,G);
- %% scenario 2: l_2(t) = 2*cos(2*pi*fc21*t)
- fc21 = 100e3;
- Tc21 = 1/fc21;
- phasedeg = 45;
- fc21t = 2*cos(2*pi*fc21*t - (phasedeg*pi/180));
- A = 0.5;
- gdemod = A*gAM.*fc21t;
- gdemod = 2*filter(b,a,gdemod);
- % FFT calculation
- [~,G,f] = myfft(gdemod,fs);
- figure('name','Demodulated Signal, scenario 2')
- % plot the time domain and frequency domain signals
- plotscript(t,gdemod,f,G);
- %% scenario 3: l_2(t) = 2*cos(2*pi*fc21*t)
- fc21 = 100e3;
- Tc21 = 1/fc21;
- phasedeg = 90;
- fc21t = 2*cos(2*pi*fc21*t - (phasedeg*pi/180));
- A = 0.5;
- gdemod = A*gAM.*fc21t;
- gdemod = 2*filter(b,a,gdemod);
- % FFT calculation
- [~,G,f] = myfft(gdemod,fs);
- figure('name','Demodulated Signal, scenario 3')
- % plot the time domain and frequency domain signals
- plotscript(t,gdemod,f,G);
- %% scenario 4: l_2(t) = 2*cos(2*pi*fc21*t)
- fc21 = 96e3;
- Tc21 = 1/fc21;
- phasedeg = 0;
- fc21t = 2*cos(2*pi*fc21*t - (phasedeg*pi/180));
- A = 0.5;
- gdemod = A*gAM.*fc21t;
- gdemod = 2*filter(b,a,gdemod);
- % FFT calculation
- [~,G,f] = myfft(gdemod,fs);
- figure('name','Demodulated Signal, scenario 4')
- % plot the time domain and frequency domain signals
- plotscript(t,gdemod,f,G);
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