function[t,st]=bpf(f,sf,B1,B2)

df=f(2)-f(1);
T=1/df;
hf=zeros(1,length(f));
bf=[floor(B1/df):floor(B2/df)];
bf1=floor(length(f)/2)+bf;
bf2=floor(length(f)/2)-bf;
hf(bf1)=1/sqrt(2*B2-B1);
hf(bf2)=1/sqrt(2*B2-B1);

yf=hf.*sf.*exp(-j*2*pi*f*0.1*T);
[t,st]=F2T(f,yf);