1、方波的合成实验。用5 项谐波合成一个频率为50Hz，幅值为 3 的方波，写出 MATLAB 程序，给出实验的结果。clear all; fs=10000; t=0:1/fs:0.1; f0=50;sum=0; subplot(211) for n=1:2:9; plot(t,3*4/pi*1/n*sin(2*pi*n*f0*t), k); hold on; end title(信号叠加前); subplot(212) for n=1:2:9; sum=sum+3*4/pi*1/n*sin(2*pi*n*f0*t); end plot(t,sum, k );title(信号叠加后); 2、编写程序，画出信号3( )( )tf tet ，(4)f t以及信号4( )jtf t e的频谱图。r=0.02;t=-5:r:5;N=200;W=2*pi;k=-N:N;w=k*W/N;f1=1*exp(-3*t).*stepfun(t,0);F=r*f1*exp(-j*t*w);F1=abs(F);p1=angle(F);subplot(3,1,1);plot(t,f1);gridxlabel(t);ylabel(f(t);title(f(t);subplot(3,1,2);plot(w,F1);xlabel(w);grid;ylabel(F(jw);subplot(3,1,3);plot(w,p1*180/pi);grid;xlabel(w);ylabel(相位（度）);-5-4-3-2-101234500.51tf(t)f(t)-8-6-4-20246800.20.4wF(jw)-8-6-4-202468-1000100w相位(度)r=0.02;t=-5:r:5;N=200;W=2*pi;k=-N:N;w=k*W/N; f1=1*exp(-3*(t-4).*stepfun(t,4); F=r*f1*exp(-j*t*w); F1=abs(F);p1=angle(F);subplot(3,1,1);plot(t,f1);grid xlabel(t);ylabel(f(t);title(f(t-4);subplot(3,1,2); plot(w,F1);xlabel(w);grid;ylabel(F(jw)的模 );subplot(3,1,3); plot(w,p1*180/pi);grid;xlabel(w);ylabel(相位 (度); R=0.02;t=-2:R:2; f=exp(-3*t).*stepfun(t,0); f1=f.*exp(-j*4*t) ; W1=2*pi*5; N=500; k=-N :N ; W=k*W1/N; F=f1*exp(-j*t*W)*R; F=real(F); plot(W,F); xlabel(W);ylabel(F(W);title(频谱 F(jw);