Question

AM Modulator AM Demodulator m(t) SAM-DSB-Sc(t) mdemod(t) LPF cos2nfct cos2nfct Figure 1 P1. For the system shown in Figure 1, sketch the signals m(t), SAM-DSB-sc(t), and mde mod (t) in the time and frequency domain, assuming m(t)=cos 20rd and that AM- DSB-SC is the modulation scheme used with f. = 100Hz P2. Repeat P1 changing m(t) to a 10 Hz square wave, with amplitude 1 (Figure 2) s(t) t 0.05 0.1 Figure 2

Answer 1

SAM-DSB-Sc It) = m(t) cos anfct Cos 2ont cos 2oont SAM-DSB-Sc Lt. cos zookt cos zont cs 2000t cos zoktfit cos 400 7t) Cos 2017 + cos Zott content m demod It)= cos zott 2

close all
clear all
clc

t=-1:0.001:1-0.001;
m=cos(20.*pi.*t);
m_f=fft(m);
n=length(m_f);fs=0.001;
f=(0:n-1)*fs/n;
s=m.*cos(200*pi.*t);
ss=fftshift(fft(s))
dem=m/2;

y=fftshift(m_f);
demy=y/2;
fshift=(-n/2:n/2-1)*(fs/n); % zero-centered frequency range

figure
plot(t,m)
xlabel('t')
ylabel('m(t)')

figure
plot(fshift,y)
xlabel('f')
ylabel('M(f)')

figure
plot(t,s)
xlabel('t')
ylabel('sAM-DSBSC(t)')

figure
plot(fshift,ss)
xlabel('f')
ylabel('sAM-DSBSC(f)')

figure
plot(t,dem)
xlabel('t')
ylabel('mdemod(t)')

figure
plot(fshift,demy)
xlabel('f')
ylabel('mdemod(f)')

m1=square(20*pi*(t+0.025));
y1=fftshift(fft(m1));
s1=m1.*cos(200*pi.*t);
ss1=fftshift(fft(s1));

figure
plot(t,s1)
xlabel('t')
ylabel('sAM-DSBSC1(t)')
axis ([-0.4 0.4 -1 1])

figure
plot(fshift,ss1)
xlabel('f')
ylabel('sAM-DSBSC1(f)')

figure
plot(t,m1/2)
xlabel('t')
ylabel('mdemod1(t)')

figure
plot(fshift,y1/2)
xlabel('f')
ylabel('mdemod1(f)')

1 0,8 0.6 0.4 0.2 m(t) 0 -0.2 -0.4 -0.6 -0.8 -1 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

1000 800 600 M(f) 400 200 0 - - -200 -5 -4 -3 -2 -1 0 1 2 3 4 5 v 10-4

0.6 0.4 SAM-DSBSC(t) -0.2 -0.4 -0.6 -0.81 1. -0.8 -0.6 -0.4 1-0.2 0.2. 0.4 10.6 1 0.8

600 1 500 400 - 300 SAM-DSBSC(f) 200 100 0 1 1 1 -100 -5 I 4 -4 -3 -2 -1 0 1 2 3 5 f *10-4

0.5 л -- П — 0.4 0.3 0.2 0.1 mdemod(t) о -0.1 -0.2 -0.3 -0.4 - -0.5 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

500 400 300 mdemod(f) 200 100 — о -100 -4 -1 4 f 5 x10:4

1 0.8 0.6 0.4 0.2 ml(t) 0 -0.2 -0.4 -0.6 -0.8 -1 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 t

1400 1200 1000 800 600 M1(f) 400 200 0 -200 -400 -600 -5 -4 -3 -2 -1 0 1 2 3 4 5 f *10-4

0.8 0.6 0.4 0.2 SAM-DSBSC1(t) 0 -0.2 -0.4 -0.6 -0.8 -0.2 -0.1 0.3

700 600 500 400 300 SAM-DSBSC1(f) 200 100 o by sending to the lead in the latest updatertentuny -100 -200 1 - -300 -5 -4 -3 -2 -1 0 1 2 3 4 5 *10-4

0.5 0.4 0.3 0.2 0.1 mdemodl(t) -0.1 -0.2 -0.3 -0.4 -0,5 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 t

700 600 500 400 300 mdemod1(f) 200 100 Он деленное-чтно-орудово-метичен ел. -100 -200 -300 -5 -4 -3 -2 -1 о 1 2 3 4 f 5 х104