WSJT-X/lib/sync4.f90

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subroutine sync4(dat,jz,mode4,minw)
! Synchronizes JT4 data, finding the best-fit DT and DF.
use jt4
parameter (NFFTMAX=2520) !Max length of FFTs
parameter (NHMAX=NFFTMAX/2) !Max length of power spectra
parameter (NSMAX=525) !Max number of half-symbol steps
real dat(jz)
real psavg(NHMAX) !Average spectrum of whole record
real s2(NHMAX,NSMAX) !2d spectrum, stepped by half-symbols
real tmp(1260)
save
! Do FFTs of twice symbol length, stepped by half symbols. Note that
! we have already downsampled the data by factor of 2.
nsym=207
nfft=2520
nh=nfft/2
nq=nfft/4
nsteps=jz/nq - 1
df=0.5*11025.0/nfft
psavg(1:nh)=0.
call timer('ps4 ',0)
do j=1,nsteps !Compute spectrum for each step, get average
k=(j-1)*nq + 1
call ps4(dat(k),nfft,s2(1,j))
psavg(1:nh)=psavg(1:nh) + s2(1:nh,j)
enddo
call timer('ps4 ',1)
call timer('flat1a ',0)
nsmo=min(10*mode4,150)
call flat1a(psavg,nsmo,s2,nh,nsteps,NHMAX,NSMAX) !Flatten spectra
call timer('flat1a ',1)
call timer('smo ',0)
if(mode4.ge.9) call smo(psavg,nh,tmp,mode4/4)
call timer('smo ',1)
ia=600.0/df
ib=1600.0/df
! ichmax=1.0+log(float(mode4))/log(2.0)
do ich=minw+1,7 !Find best width
kz=nch(ich)/2
! Set istep>1 for wide submodes?
do i=ia+kz,ib-kz !Find best frequency channel for CCF
call timer('xcor4 ',0)
call xcor4(s2,i,nsteps,nsym,ich,mode4)
call timer('xcor4 ',1)
enddo
enddo
return
end subroutine sync4