MATLAB幅度调制与解调源程序.doc

源程序clcT=0.001; %采样周期fs=1/T; %采样频率Tp=1;%观察时间N=Tp/T;%采样点n=-N/2:(N-1)/2;t=n*T; Yi=sin(40*pi*t); %调制信号subplot (211);plot (t,Yi);xlabel(t);ylabel(幅度);title(调制信号);axis(0,.5,-1,1);Yk=fft (Yi,2048) ;%对调制信号进行傅立叶变换Yw=2*pi/N*abs (fftshift (Yk) ;Fw=-1024:1023 /2048*fs;subplot (212);plot (Fw,Yw);xlabel(频率/hz);ylabel(调制信号频谱幅度);title(调制信号频谱); axis(-40,40,0,3);figurey1=cos(200*pi*t); %调制信号 subplot(211);plot(t,y1); xlabel(t);ylabel(幅度);title(载波信号);axis(0,.1,-1,1);fm=20;fs=1000;N=512;Y2=fft(y1,N);% 对调制信号进行傅里叶变换 yw=abs(fftshift(Y2);fw=-255:256/N*fs;subplot(212); plot(fw,yw); xlabel(频率/hz);ylabel(载波信号频谱幅度);title(载波信号频谱); axis(-200,200,0,100);clcT=0.01; %采样周期fs=1/T; %采样频率Tp=10;N=Tp/T;n=0:N-1;t=n*T;Yi=cos (pi*t) .*cos (20*pi*t) ; %调制后信号subplot (211);plot (t,Yi);grid;Yk=fft (Yi,2048) ;%对调制后信号进行傅立叶变换Yw=2*pi/N*abs (fftshift (Yk) ;Fw=-1024:1023 /2048*fs;subplot (212);plot (Fw,Yw);grid; fs=1000;t=0:1/fs:.8;fc=100;y=sin(pi*40*t);x=modulate(y,fc,fs,amdsb-tc); %双边带调幅subplot(211);plot(t,x);title(双边带调幅波形);subplot(212);p=fft(x,1024);p1=fftshift(p);w=0:511;p2=abs(p1);plot(w,p2(1:512);title(双边带调幅频谱);axis(300,500,-10,500)t=-1:0.001:1; A0=1; %载波信号振幅 A1=1; %调制信号振幅 A2=1; %已调信号振幅 f=100; %载波信号频率 w0=2*f*pi; m=0.1; %调制度 Uc=A0.*cos(w0*t); %载波信号 subplot(5,2,1);plot(t,Uc); title(载波信号);axis(-0.1,0.1,-1,1);grid on;T1=fft(Uc); subplot(5,2,2); plot(abs(T1); title(载波信号频谱); axis(0,400,0,1000);grid on; mes=A1*cos(40*pi*t); %调制信号subplot(5,2,3); plot(t,mes); title(调制信号);axis(-.5,.5,-1,1);grid on;T2=fft(mes); subplot(5,2,4);plot(abs(T1); title(调制信号频谱); axis(0,400,0,1000);grid on; Udsb=mes.*Uc; %DSB 已调信号subplot(5,2,5);plot(t,Udsb); title(DSB已调波形); axis(-.1,.1,-1.5,1.5);grid on;subplot(5,2,6); T3=fft(Udsb); % 对DSB已调信号进行傅里叶变换 plot(abs(T3); title(DSB已调频谱); axis(0,400,0,600);grid on; Ddsb=Udsb.*cos(w0*t); % 对DSB调制信号进行解调 subplot(5,2,7); plot(t,Ddsb); title(滤波前的DSB解调信号波形);grid on;axis(-0.1,0.1,-1,1);T4=fft(Ddsb); %求DSB信号的频谱 subplot(5,2,8); plot(abs(T4); title(滤波前的DSB解调信号频谱);grid on; axis(0,80,0,600); Ft=1000; Fp=80; %通带边界频率Fs=100; %阻带截止频率 wp=2*pi*Fp/Ft;ws=2*pi*Fs/Ft; fp=2*Ft*tan(wp/2);fs=2*Fs*tan(wp/2); n11,wn11=buttord(wp,ws,1,50,s); %求低通滤波器的阶数和截止频率 b11,a11=butter(n11,wn11,s); %求S域的频率响应的参数 num11,den11=bilinear(b11,a11,0.5); %双线性变换实现S域到Z域的变换 h,w=freqz(num11,den11); %根据参数求出频率响应z11=filter(num11,den11,Ddsb); %IIR滤波器滤波 subplot(5,2,9); plot(t,z11,r); title(滤波后的DSB解调信号波形);axis(-0.5,0.5,-1,1);grid on;T5=fft(z11); %求DSB信号的频谱subplot(5,2,10); plot(abs(T5),r);title(滤波后的DSB解调信号频谱); axis(0,80,0,600);grid on;2 燕庆明主编.信号与系统M. 高等教育出版社, 20013 樊昌信等编.通信原理M. 国防工业出版社, 1995clcT=0.001; %采样周期fs=1/T; %采样频率Tp=10;N=Tp/T;n=0:N-1;t=n*T;Yi=sin (40*pi*t).*cos(200*pi*t); %调制后信号subplot (211);plot (t,Yi);title(DSB已调波形); axis(0,.3,-1,1);Yk=fft (Yi,2048) ;%对调制后信号进行傅立叶变换Yw=2*pi/N*abs (fftshift (Yk) ;Fw=-1024:1023 /2048*fs;subplot (212);plot (Fw,Yw);title(DSB已调频谱); axis(-200,200,0,.1);clcT=0.001; %采样周期fs=1/T; %采样频率Tp=10;N=Tp/T;n=0:N-1;t=n*T;Yi=sin (40*pi*t); %调制信号subplot (211);plot (t,Yi);title(调制信号);axis(