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t=0:pi/100:4*pi; s=sin(t+3*pi/4); plot(s); title('原始信号s'); %==================================== %对s进行小波分解：db1 3层 [c,l]=wavedec(s,3,'db1'); %==================================== %提取小波分解的低频系数a

%频率变换，低通、高通、带通、带阻函数分别为lp2lp,lp2hp,lp2bp,lp2bs %page_353 upper %怎样才能和书上作出一样的图呢？？？？？？？？？？？？？？？？？？ [z,p,k]=buttap(3);%3 pole filter [num,den]=zp2tf(z,p,k);%convert to polynoials wb=5*2*pi; %new ban

n=-10:10; x=cos(pi/8*(n.^2)); stem(n,x,'filled');%用来画离散的信号 axis([-10,10,-1,1]); xlabel('n'); ylabel('x[n]');

%求一个连续信号的傅里叶变换 %CTFT syms x t X w %x表示时域信号，X表示fourier变换 a=2;b=2; x=exp(-a*t)*sin(b*pi*t); X=simplify(int(x*exp(-j*w*t),t,0,inf));

%设计一个切比雪夫1型高通滤波器，其模拟截止频率wc=2 %page_413 N=2;%number of poles Rp=3;%passband ripple T=.2;%sampling period wc=2;%analog cutoff frequency Wc=wc*T/pi;%normalized digital cutoff frequency [numd,dend

%求一个连续信号的傅里叶变换 %CTFT syms x t X w %x表示时域信号，X表示fourier变换 a=2;b=2; x=exp(-a*t)*sin(b*pi*t); X=simplify(int(x*exp(-j*w*t),t,0,inf));

%带通信号经过带通系统的等效基带表示 clear all; close all; dt = 0.01; t = 0:dt:5; s1 = exp(-t).*cos(20*pi*t); %输入信号 [f1 s1f]= T2F(t,s1); %输入信号的频谱 s1_lowpass = hilbert(s1).*exp(-j*2*pi*

%方波的频谱（直接画） close all; clear all; T=1; N=128; df=1/T/N; f = -100*N/2*df:df:100*N/2*df-df; sf= T^2*j*pi*f*0.5.*exp(-j*2*pi*f*T).*sinc(f*T*0.5).*sinc(f*T*0.5); plot(f,abs(sf))

%FM modulation and demodulation clear all; close all; Kf = 5; fc = 10; T=5; dt=0.001; t = 0:dt:T; %信源 fm= 1; %mt = cos(2*pi*fm*t) + 1.5*sin(2*pi*0.3*fm*t); %信源信号 mt = cos(2

%低通抽样定理 clear all; close all; dt = 0.01; t = 0:dt:10; xt = 0.1*cos(0.15*pi*t)+1.5*sin(2.5*pi*t)+0.5*cos(4*pi*t); [f,xf] = T2F(t,xt); %抽样信号，抽样速率为4Hz fs = 4; sdt = 1/fs; t1 = 0:sdt:10; st