subroutine baseline(s,nfa,nfb,sbase) ! Fit baseline to spectrum (for FT8) ! Input: s(npts) Linear scale in power ! Output: sbase(npts) Baseline implicit real*8 (a-h,o-z) real*4 s(1920) real*4 sbase(1920) real*4 base real*8 x(1000),y(1000),a(5) data nseg/10/,npct/10/ df=12000.0/3840.0 !3.125 Hz ia=max(1,nint(nfa/df)) ib=nint(nfb/df) do i=ia,ib s(i)=10.0*log10(s(i)) !Convert to dB scale enddo nterms=5 nlen=(ib-ia+1)/nseg !Length of test segment i0=(ib-ia+1)/2 !Midpoint k=0 do n=1,nseg !Loop over all segments ja=ia + (n-1)*nlen jb=ja+nlen-1 call pctile(s(ja),nlen,npct,base) !Find lowest npct of points do i=ja,jb if(s(i).le.base) then if (k.lt.1000) k=k+1 !Save all "lower envelope" points x(k)=i-i0 y(k)=s(i) endif enddo enddo kz=k a=0. call polyfit(x,y,y,kz,nterms,0,a,chisqr) !Fit a low-order polynomial sbase=0.0 do i=ia,ib t=i-i0 sbase(i)=a(1)+t*(a(2)+t*(a(3)+t*(a(4)+t*(a(5))))) + 0.65 ! write(51,3051) i*df,s(i),sbase(i) !3051 format(3f12.3) enddo return end subroutine baseline