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DSP/Untitled.m

+n=1;
+f1=100; f2=300;
+fs=1000;%采样频率?
+t=0:1/fs:n;
+fre=10;
+y1=square(2*fre*pi*t)/2;
+y2=square(2*fre*pi*t)/2;
+dt=1/fs;%定义时间步长?
+n1=length(t);%样点个数?
+f_end=1/dt;%频率轴的显示范围?
+f=(0:n1-1)*f_end/n1-f_end/2;%频率自变量?
+Xf1=dt*fftshift(fft(y1));%频谱?
+Xf2=dt*fftshift(fft(y2));
+figure(1);
+subplot(211);plot(t,y1);xlabel('t');title('基带信号时域图');
+subplot(212);plot(f,abs(Xf1));xlabel('f');title('基带信号频谱');
+
+z1=1*sin(2*pi*f1*t);
+z2=1*sin(2*pi*f2*t);
+figure(2);
+subplot(221);plot(t,z1);xlabel('t');title('100Hz正弦波时域图');
+subplot(222);plot(f,abs(dt*fftshift(fft(z1))));xlabel('f');title('100Hz正弦波幅度频谱');
+subplot(223);plot(t,z2);xlabel('t');title('300Hz正弦波时域图');
+subplot(224);plot(f,abs(dt*fftshift(fft(z2))));xlabel('f');title('300Hz正弦波幅度频谱');
+
+yy1=y1.*z1;%信号相乘?
+yy2=y2.*z2;
+yy3=yy1+yy2;
+
+Xf3=dt*fftshift(fft(yy1));
+figure(3);
+subplot(411);plot(t,yy1);xlabel('t');title('调制信号1时域');
+subplot(412);plot(f,abs(Xf3));xlabel('f');title('调制信号1频谱');
+
+Xf4=dt*fftshift(fft(yy2));
+figure(3);
+subplot(413);plot(t,yy2);xlabel('t');title('调制信号2时域');
+subplot(414);plot(f,abs(Xf4));xlabel('f');title('调制信号2频谱');
+
+Xf5=dt*fftshift(fft(yy3));
+figure(4);
+subplot(211);plot(t,yy3);xlabel('t');title('调制信号1+2时域');
+subplot(212);plot(f,abs(Xf5));xlabel('f');title('调制信号1+2频谱');
+
+fp1=50;fp2=150;%FIR滤波器100Hz?
+fs1=0;fs2=200;
+As=15;
+Ws1=(fp1+fs1)/fs; Ws2=(fp2+fs2)/fs;
+w=(fp1-fs1)/fs;
+M=ceil((As-7.95)/(14.36*w));
+H=hamming(M+1);
+b=fir1(M,[Ws1,Ws2],H);
+% figure(5);
+% freqz(b,1,fs,fs);title('FIR滤波器50-150Hz');
+
+t=0:1/fs:n;
+yyy1=filter(b,2,yy3);%信号1+2经过滤波器1?
+% zz1=filter(b,2,z1);%100Hz正弦波经过滤波器1
+Xf10=dt*fftshift(fft(yyy1)); Xf11=dt*fftshift(fft(zz1));
+figure(7);
+subplot(411);plot(t,yyy1);xlabel('t');title('信号1+2经滤波器1后时域图');
+subplot(412);plot(f,abs(Xf10));xlabel('f');title('信号1+2经滤波器1后频谱');
+% figure(8);
+% subplot(212);plot(f,abs(zz1));xlabel('f');title('100Hz正弦波滤波器1后频谱');
+% subplot(212);plot(f,abs(zz1));xlabel('f');title('100Hz正弦波滤波器1后频谱');
+
+fp1=250;fp2=350;%FIR滤波器300Hz?
+fs1=200;fs2=400;
+As=15;
+Ws1=(fp1+fs1)/fs; Ws2=(fp2+fs2)/fs;
+w=(fp1-fs1)/fs;
+M=ceil((As-7.95)/(14.36*w));
+H2=hamming(M+1);
+b=fir1(M,[Ws1,Ws2],H2);
+% figure(9);
+% freqz(b,1,fs,fs);title('FIR滤波器250-350Hz');
+
+t=0:1/fs:n;
+yyy2=filter(b,2,yy3);
+% zz2=filter(b,2,z2);
+Xf12=dt*fftshift(fft(yyy2));
+Xf13=dt*fftshift(fft(zz2));
+figure(7);
+subplot(413);plot(t,yyy2);xlabel('t');title('信号1+2经滤波器2后时域图');
+subplot(414);plot(f,abs(Xf12));xlabel('f');title('信号1+2经滤波器2后频谱');
+% figure(11);
+% subplot(211);plot(t,zz2);xlabel('t');title('300Hz正弦波滤波器2后时域图');
+% subplot(212);plot(f,abs(zz2));xlabel('f');title('300Hz正弦波滤波器2后频谱');
+
+k1=yyy1.*z1;%解调?
+k2=yyy2.*z2;
+% figure(12);
+% subplot(211);plot(t,k1);xlabel('t');title('解调信号1时域图');
+% subplot(212);plot(f,abs(dt*fftshift(fft(k1))));xlabel('f');title('解调信号1频谱');
+% figure(13);
+% subplot(211);plot(t,k2);xlabel('t');title('解调信号2时域图');
+% subplot(212);plot(f,abs(dt*fftshift(fft(k2))));xlabel('f');title('解调信号2频谱');
+
+N=8;%8阶巴特沃斯低通滤波器上限频率100Hz?
+Wn=100/(fs/2);
+[b,a]=butter(N,Wn,'low');
+
+kk1=filter(b,a,k1);
+kk2=filter(b,a,k2);
+% figure(14);
+[H,W]=freqz(b,a);%返回频率响应
+% subplot(211);plot(W*fs/(2*pi),abs(H));xlabel('频率Hz');ylabel('幅值');
+% grid on;
+% subplot(212);plot(W*fs/(2*pi),20*log10(abs(H)));xlabel('频率Hz');ylabel('幅值dB');
+% grid on;
+
+Xf6=dt*fftshift(fft(kk1));
+Xf7=dt*fftshift(fft(kk2));
+figure(15);
+subplot(211);plot(t,kk1);xlabel('t');title('解调信号1经滤波时域');
+subplot(212);plot(f,abs(Xf6));xlabel('f');title('解调信号1经滤波频谱');
+figure(16);
+subplot(211);plot(t,kk2);xlabel('t');title('解调信号2经滤波时域');
+subplot(212);plot(f,abs(Xf7));xlabel('f');title('解调信号2经滤波频谱');
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