mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2025-10-31 13:10:19 -04:00
5ca81a6507
polynomial fit is done over 400 Hz bandwidth for T/R periods longer than 15s, and over approx. 600 Hz (10 times the signal bandwidth) for T/R period of 15s.
49 lines
1.2 KiB
Fortran
49 lines
1.2 KiB
Fortran
subroutine fst4_baseline(s,np,ia,ib,npct,sbase)
|
|
|
|
! Fit baseline to spectrum (for FST4)
|
|
! Input: s(npts) Linear scale in power
|
|
! Output: sbase(npts) Baseline
|
|
|
|
implicit real*8 (a-h,o-z)
|
|
real*4 s(np),sw(np)
|
|
real*4 sbase(np)
|
|
real*4 base
|
|
real*8 x(1000),y(1000),a(5)
|
|
data nseg/8/
|
|
|
|
do i=ia,ib
|
|
sw(i)=10.0*log10(s(i)) !Convert to dB scale
|
|
enddo
|
|
|
|
nterms=3
|
|
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(sw(ja),nlen,npct,base) !Find lowest npct of points
|
|
do i=ja,jb
|
|
if(sw(i).le.base) then
|
|
if (k.lt.1000) k=k+1 !Save all "lower envelope" points
|
|
x(k)=i-i0
|
|
y(k)=sw(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))) + 0.2
|
|
! write(51,3051) i,sw(i),sbase(i)
|
|
!3051 format(i8,2f12.3)
|
|
enddo
|
|
|
|
sbase=10**(sbase/10.0)
|
|
|
|
return
|
|
end subroutine fst4_baseline
|