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subroutine sync8(dd,nfa,nfb,syncmin,nfqso,maxcand,s,candidate, &
ncand,sbase)
include 'ft8_params.f90'
parameter (MAXPRECAND=500)
! Search over +/- 2.5s relative to 0.5s TX start time.
parameter (JZ=62)
complex cx(0:NH1)
real s(NH1,NHSYM)
real savg(NH1)
real sbase(NH1)
real x(NFFT1)
real sync2d(NH1,-JZ:JZ)
real red(NH1)
real candidate0(3,MAXPRECAND)
real candidate(3,maxcand)
real dd(NMAX)
integer jpeak(NH1)
integer indx(NH1)
integer ii(1)
integer icos7(0:6)
data icos7/3,1,4,0,6,5,2/ !Costas 7x7 tone pattern
equivalence (x,cx)
! Compute symbol spectra, stepping by NSTEP steps.
savg=0.
tstep=NSTEP/12000.0
df=12000.0/NFFT1 !3.125 Hz
fac=1.0/300.0
do j=1,NHSYM
ia=(j-1)*NSTEP + 1
ib=ia+NSPS-1
x(1:NSPS)=fac*dd(ia:ib)
x(NSPS+1:)=0.
call four2a(x,NFFT1,1,-1,0) !r2c FFT
do i=1,NH1
s(i,j)=real(cx(i))**2 + aimag(cx(i))**2
enddo
savg=savg + s(1:NH1,j) !Average spectrum
enddo
call get_spectrum_baseline(dd,nfa,nfb,sbase)
ia=max(1,nint(nfa/df))
ib=nint(nfb/df)
nssy=NSPS/NSTEP ! # steps per symbol
nfos=NFFT1/NSPS ! # frequency bin oversampling factor
jstrt=0.5/tstep
candidate0=0.
k=0
do i=ia,ib
do j=-JZ,+JZ
ta=0.
tb=0.
tc=0.
t0a=0.
t0b=0.
t0c=0.
do n=0,6
m=j+jstrt+nssy*n
if(m.ge.1.and.m.le.NHSYM) then
ta=ta + s(i+nfos*icos7(n),m)
t0a=t0a + sum(s(i:i+nfos*6:nfos,m))
endif
tb=tb + s(i+nfos*icos7(n),m+nssy*36)
t0b=t0b + sum(s(i:i+nfos*6:nfos,m+nssy*36))
if(m+nssy*72.le.NHSYM) then
tc=tc + s(i+nfos*icos7(n),m+nssy*72)
t0c=t0c + sum(s(i:i+nfos*6:nfos,m+nssy*72))
endif
enddo
t=ta+tb+tc
t0=t0a+t0b+t0c
t0=(t0-t)/6.0
sync_abc=t/t0
t=tb+tc
t0=t0b+t0c
t0=(t0-t)/6.0
sync_bc=t/t0
sync2d(i,j)=max(sync_abc,sync_bc)
enddo
enddo
red=0.
do i=ia,ib
ii=maxloc(sync2d(i,-JZ:JZ)) - 1 - JZ
j0=ii(1)
jpeak(i)=j0
red(i)=sync2d(i,j0)
enddo
iz=ib-ia+1
call indexx(red(ia:ib),iz,indx)
npctile=nint(0.40*iz)
if(npctile.lt.1) then ! something is wrong; bail out
ncand=0
return;
endif
ibase=indx(npctile) - 1 + ia
if(ibase.lt.1) ibase=1
if(ibase.gt.nh1) ibase=nh1
base=red(ibase)
red=red/base
do i=1,min(MAXPRECAND,iz)
n=ia + indx(iz+1-i) - 1
if(red(n).lt.syncmin.or.isnan(red(n)).or.k.eq.MAXPRECAND) exit
k=k+1
candidate0(1,k)=n*df
candidate0(2,k)=(jpeak(n)-0.5)*tstep
candidate0(3,k)=red(n)
enddo
ncand=k
! Save only the best of near-dupe freqs.
do i=1,ncand
if(i.ge.2) then
do j=1,i-1
fdiff=abs(candidate0(1,i))-abs(candidate0(1,j))
if(abs(fdiff).lt.4.0) then
if(candidate0(3,i).ge.candidate0(3,j)) candidate0(3,j)=0.
if(candidate0(3,i).lt.candidate0(3,j)) candidate0(3,i)=0.
endif
enddo
endif
enddo
fac=20.0/maxval(s)
s=fac*s
! Sort by sync
call indexx(candidate0(3,1:ncand),ncand,indx)
! Place candidates within 10 Hz of nfqso at the top of the list
k=1
do i=1,ncand
if( abs( candidate0(1,i)-nfqso ).le.10.0 .and. candidate0(3,i).ge.syncmin ) then
candidate(1:3,k)=candidate0(1:3,i)
candidate0(3,i)=0.0
k=k+1
endif
enddo
do i=ncand,1,-1
j=indx(i)
if( candidate0(3,j) .ge. syncmin ) then
candidate(2:3,k)=candidate0(2:3,j)
candidate(1,k)=abs(candidate0(1,j))
k=k+1
if(k.gt.maxcand) exit
endif
enddo
ncand=k-1
return
end subroutine sync8
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