实验四matlab

Mstg函数

function st=mstg

N=800

Fs=10000;T=1/Fs;Tp=N*T;

t=0:T:(N-1)*T;k=0:N-1;f=k/Tp;

fc1=Fs/10;

fm1=fc1/10;

fc2=Fs/20;

fm2=fc2/10;

fc3=Fs/40;

fm3=fc3/10;

xt1=cos(2*pi*fm1*t).*cos(2*pi*fc1*t);

xt2=cos(2*pi*fm2*t).*cos(2*pi*fc2*t);

xt3=cos(2*pi*fm3*t).*cos(2*pi*fc3*t);

st=xt1+xt2+xt3;

fxt=fft(st,N);

subplot(3,1,1)

plot(t,st);grid;xlabel('t/s');ylabel('s(t)');

axis([0,Tp/8,min(st),max(st)]);title('(a) s(t)的波形') subplot(3,1,2)

stem(f,abs(fxt)/max(abs(fxt)),'.');grid;title('(b) s(t)的频谱') axis([0,Fs/5,0,1.2]);

xlabel('f/Hz');ylabel('幅度')

调幅信号y1(n)

fp1=300;fs1=400;Fs=10000;T=1/Fs;

wp1=2*fp1/Fs;ws1=2*fs1/Fs;

rp=0.1;rs=60;

[N,wn1]=ellipord(wp1,ws1,rp,rs);

[b1,a1]=ellip(N,rp,rs,wn1);

st1=mstg

y1=filter(b1,a1,st1);

[H,W]=freqz(b1,a1);

m=abs(H);

figure(2);subplot(3,1,1)

plot(W/pi,20*log10(m/max(m)));grid;xlabel('频率（Hz）');ylabel('幅度（dB）');title('(c) H1(z)的幅频特性')

subplot(3,1,2)

N=800;Tp=N*T;t=0:T:(N-1)*T;k=0:N-1;f=k/Tp;

plot(t,y1);grid;xlabel('t/s');ylabel('y1');

axis([0,Tp/8,min(y1),max(y1)]);title('(d) y1的波形')

Y1=fft(y1)

k=0:N-1;

subplot(3,1,3)

plot(f,abs(Y1));

stem(f,abs(Y1)/max(abs(Y1)),'.');grid;title('(e) y1的频谱')

axis([0,Fs/5,0,1.2]);

xlabel('f/Hz');ylabel('幅度')

调幅信号y2(n)

fp2=460,fpu=540;fs2=400,fsu=600;Fs=10000;T=1/Fs;

wp2=2*[fp2,fpu]/Fs;ws2=2*[fs2,fsu]/Fs;

rp=0.1;rs=60;

[N,wn2]=ellipord(wp2,ws2,rp,rs);

[b2,a2]=ellip(N,rp,rs,wn2);

st2=mstg

y2=filter(b2,a2,st2);

[H,W]=freqz(b2,a2);

m=abs(H);

figure(2);subplot(3,1,1)

plot(W/pi,20*log10(m/max(m)));grid;xlabel('频率（kHz）');ylabel('幅度（dB）');title('(c2) H2(z)的幅频特性')

subplot(3,1,2)

N=800;Tp=N*T;t=0:T:(N-1)*T;k=0:N-1;f=k/Tp;

plot(t,y2);grid;xlabel('t/s');ylabel('y2');

axis([0,Tp/8,min(y2),max(y2)]);title('(d2) y2的波形')

Y2=fft(y2)

k=0:N-1;

subplot(3,1,3)

plot(f,abs(Y2));

stem(f,abs(Y2)/max(abs(Y2)),'.');grid;title('(e2) y2的频谱')

axis([0,Fs/5,0,1.2]);

xlabel('f/Hz');ylabel('幅度')

调幅信号y3(n)

fp3=1150;fs3=700;Fs=10000;T=1/Fs;

wp3=2*fp3/Fs;ws3=2*fs3/Fs;

rp=0.1;rs=60;

[N,wn3]=ellipord(wp3,ws3,rp,rs);

[b3,a3]=ellip(N,rp,rs,wn3,'high');

st3=mstg

y3=filter(b3,a3,st3);

[H,W]=freqz(b3,a3);

m=abs(H);

figure(2);subplot(3,1,1)

plot(W/pi,20*log10(m/max(m)));grid;xlabel('频率（Hz）');ylabel('幅度

（dB）');title('(c3) H3(z)的幅频特性')

subplot(3,1,2)

N=800;Tp=N*T;t=0:T:(N-1)*T;k=0:N-1;f=k/Tp;

plot(t,y3);grid;xlabel('t/s');ylabel('y3');

axis([0,Tp/8,min(y3),max(y3)]);title('(d3) y3的波形')

Y3=fft(y3)

k=0:N-1;

subplot(3,1,3)

plot(f,abs(Y3));

stem(f,abs(Y3)/max(abs(Y3)),'.');grid;title('(e3) y3的频谱')

axis([0,Fs/5,0,1.2]);

xlabel('f/Hz');ylabel('幅度')