% ex_09_10_1.m :  習題 9.10

clear all;
close all;

t=0:0.01:3;
a(1:100)=1;
a(101:200)=-1;
a(201:301)=1;
fs=1;
fc=.3; 
figure('color','w');
subplot(421)
plot(t,a)
ylabel('a(t)')
axis([0 3 -1.1 1.1])

%
y1=modulate(a,fc,fs,'am');
subplot(423)
plot(y1)
ylabel('  for "am"')
 
y2=modulate(a,fc,fs,'fm');
subplot(425)
plot(y2)
ylabel('  for "fm"')
 
y3=modulate(a,fc,fs,'pm',1);
subplot(427)
plot(y3)
ylabel('  for "pm"')
 
%
a1=demod(y1,fc,fs,'am');
subplot(424)
plot(a1)
ylabel('  for "am"')
 
a2=demod(y2,fc,fs,'fm');
subplot(426)
plot(a2)
ylabel('  for "fm"')
 
a3=demod(y3,fc,fs,'pm',1);
subplot(428)
plot(a3)
ylabel('  for "pm"')