%實(shí)驗一
%余弦信號的傅立葉變換
global dt df N t f T %全局變量
close all
N=2^15;      %采樣點(diǎn)數(shù)
% L=64;			%每碼元的采樣點(diǎn)數(shù)
% M=N/L;			%碼元數(shù)
M=2^6;%碼元數(shù)
dt=0.001;    %時域采樣間隔
df=1/(N*dt);%頻域采樣間隔
T=N*dt;     %截短時間
Bs=N*df/2;  %系統(tǒng)帶寬
t=linspace(-T/2,T/2,N);
f=linspace(-Bs,Bs,N);
a=round(rand(1,M));	
fl=3.1;
fh=10.6;
f0=fh;
B1=(fh-fl)/M;
s=zeros(1,N);
S=zeros(1,N);
sn=cos(2*pi*f0*t);
for k=1:M
    f0=fl+(k-0.5)*B1;
    sn=cos(2*pi*f0*t);
    Sn=(2*aabs(t2f(sn));
    s=sn+s;
end
S=t2f(s);
%a=f2t(S);
figure(1)
set(1,'position',[10,50,300,200])%設(shè)定窗口位置及大小
figure(2)
set(2,'position',[350,50,300,200]);%設(shè)定窗口位置及大小
figure(1)
as=abs(S);  %求模
plot(f,as,'g')
grid;
axis([-20,+20,min(S),max(S)]);
xlabel('f(kHZ)');
ylabel('S(f)(V/kHZ)');
figure(2)
plot(t,s,'b')
grid
axis([-5,+5,-1.5,1.5']);
xlabel(('t(ms)'));
ylabel('s(t)(V)');