1、Vm0=2;ka=0.25;n=-t0/2:1/fs:t0/2;w=0:1/(N-1):1;x=5*cos(200*pi*n); %调制信号y=Vm0*(1+ka*x/Vm0).*cos(2*pi*fc*n);h=Vm0*cos(2*pi*fc*n);figure(1)subplot(2,2,1)plot(n,x)title(调制信号);subplot(2,2,2)plot(n,y)已调波信号subplot(2,2,3)plot(n,h) 载波信号axis(-0.01,0.01,-5,5);H=fft(h);subplot(2,2,4)plot(w,abs(H) 载波频谱axis(0,1,0,
2、500);N=length(x);X=fft(x);Y=fft(y);2*pi/(N-1):2*pi;figure(2)subplot(2,1,1)plot(w,abs(X)axis(0,1,0,3000);调制信号频谱subplot(2,1,2)plot(w,abs(Y)axis(0,1,0,1200);已调波信号频谱y1=y-2*cos(800*pi*n);y2=Vm0*y1.*cos(2*pi*fc*n);wp=40/N*pi;ws=60/N*pi;Rp=1;As=15;T=1;OmegaP=wp/T;OmegaS=ws/T;cs,ds=afd_butt(OmegaP,OmegaS,Rp
3、,As);b,a=imp_invr(cs,ds,T);y=filter(b,a,y2);figure(3)解调波axis(0,1,0,1000);解调信号频谱x=3*cos(200*pi*n)-2*cos(250*pi*n);N=length(X);axis(0,pi/4,0,3000);axis(pi/6,pi/4,0,1200);y1=y-2*cos(2000*pi*n);axis(0,pi/6,0,1000);%抑制载波双边带调制y=amod(x,t,fs,t0,fc,Vm0,ka)要求fs% x调制信号, t0采样区间,fs采样频率, y=Vm0*x.*cos(2*pi*fc*n);axis(pi/6,pi/4,0,2000);axis(0,pi/6,0,3000);axis(0,pi/6,0,2000);%单边带调制y=amod(x,t,fs,t0,fc,Vm0,ka)要求fs% x调制信号,t0采样区间,fs采样频率, N=length(n);x2=hilbert(x1,N);y=(Vm0*x1.*cos(2*pi*fc*n)-Vm0*x2.*sin(2*pi*fc*n)/2;plot(n,x1)X=fft(x1);axis(pi/6,pi/4,0,3000);title(解调波频谱)x1=3*cos(200*pi*n)-2*cos(250*pi*n);