%
% Example 10.4 and Figures 10.6, 10.7, and 10.8
%
t=0:0.01:7
x=t.*exp(-t)
% modulated signal and its plot
% Figure 10.6, wc=20
wc=20;
xmod=x.*cos(wc*t)
figure (1)
plot(t,xmod,t,x,'--')
xlabel('time in seconds')
ylabel('modulated and original signals')
grid
print -deps fig10_6.eps
% modulated signal and its plot
% Figure 10.7, wc=2
wc=2;
xmod=x.*cos(wc*t)
figure (2)
plot(t,xmod,t,x,'--')
xlabel('time in seconds')
ylabel('modulated and original signals')
grid
print -deps fig10_7.eps
%
% spectrum of the original signal
%
% Figure 10.8
%
w=0:0.01:wc
num=1
den=[1 2 1]
X=freqs(num,den,w)
magX=abs(X)
figure (3)
plot(w,magX)
xlabel('angular frequency in rad/sec')
ylabel('magnitude spectrum of x(t)')
grid
print -deps fig10_8.eps