close all;

clear all;

Fs=8000;% sampling rate 8000 per sec

Fc=1000; %in hertz

Fm=10;% Modulating frequency in hertz

t=linspace(0,0.2,Fs);

ka=0.5;

x=cos(2*pi*Fm.*t);

%y=ammod(x,Fc,Fs)

c=cos(2*pi*Fc.*t);

y=(1+ka*x).*cos(2*pi*Fc.*t);

figure

plot(t,x)

figure

plot(t,c)

figure

plot(t,y)

for I=1:8000, % rectification

if y(I)

y(I)=0;

end

end

figure

plot(t, y)

z=fft(y);

f = (0:length(y)-1)*8000/length(y);

figure

plot(f,abs(z))

for I=30:8000, %filering

z(I)=0;

end

q=ifft(z);

%plot(t, abs(q))

figure;

subplot(2,1,1);

plot(t,x)

subplot(2,1,2);

plot(t,abs(q))

[15 points] 1) In Amplitude Modulation, what is over-modulation, under-modulation and 100% modulation? Draw the modulated waves in each case [20 points) 2) Assume that m(t) = cos (2 *** m*1) Describe the operation of a Costas receiver for DSB-SC signal. Derive mathematical equations shown for the receiver in class 125 points) 3) Use the attached Matlab code, and set ka=0.25, 1.00 and 1.25. Plot the modulated and demodulated signals. When does the phase reversal occur? What is the drawback of that? [25 points) 4) Use the attached Matlab code, and set ka=0.5. Plot the modulated and demodulated waves for fm=10 Hz, 100 Hz and 500Hz. What can be concluded from the modulated waves? [15 points] 5) Draw the block diagram of a communication system. Describe the necessity of each block in the diagram