WSJT-X/lib/sync66.f90

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subroutine sync66(iwave,nmax,mode66,nsps,nfqso,ntol,xdt,f0,snr1)
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parameter (NSTEP=4) !Quarter-symbol steps
integer*2 iwave(0:nmax-1) !Raw data
integer b11(11) !Barker 11 code
integer ijpk(2) !Indices i and j at peak of sync_sig
real, allocatable :: s1(:,:) !Symbol spectra
real, allocatable :: x(:) !Work array; demoduated 2FSK sync signal
real sync(4*85) !sync vector
real sync_sig(-64:64,-15:15)
complex, allocatable :: c0(:) !Complex spectrum of symbol
data b11/1,1,1,0,0,0,1,0,0,1,0/ !Barker 11 code
data sync(1)/99.0/
save sync
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nfft=2*nsps
df=12000.0/nfft
istep=nsps/NSTEP
iz=5000.0/df !Uppermost frequency bin, at 5000 Hz
txt=85.0*nsps/12000.0
jz=(txt+1.0)*12000.0/istep !Number of quarter-symbol steps
if(nsps.ge.7680) jz=(txt+2.0)*12000.0/istep !For TR 60 s and higher
allocate(s1(iz,jz))
allocate(x(jz))
allocate(c0(0:nsps))
if(sync(1).eq.99.0) then
sync=0.
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do k=1,22
kk=k
if(kk.gt.11) kk=k-11
i=4*NSTEP*(k-1) + 1
sync(i)=2.0*b11(kk) - 1.0
enddo
endif
fac=1/32767.0
do j=1,jz !Compute symbol spectra at quarter-symbol steps
ia=(j-1)*istep
ib=ia+nsps-1
k=-1
do i=ia,ib,2
xx=iwave(i)
yy=iwave(i+1)
k=k+1
c0(k)=fac*cmplx(xx,yy)
enddo
c0(k+1:nfft/2)=0.
call four2a(c0,nfft,1,-1,0) !r2c FFT
do i=1,iz
s1(i,j)=real(c0(i))**2 + aimag(c0(i))**2
enddo
enddo
i0=nint(nfqso/df)
call pctile(s1(i0-64:i0+192,1:jz),129*jz,40,base)
s1=s1/base
s1max=20.0
! Apply AGC
do j=1,jz
x(j)=maxval(s1(i0-64:i0+192,j))
if(x(j).gt.s1max) s1(i0-64:i0+192,j)=s1(i0-64:i0+192,j)*s1max/x(j)
enddo
sync_sig=0.
ia=min(64,nint(ntol/df))
dt4=nsps/(NSTEP*12000.0) !duration of 1/4 symbol
! lag2=nint(0.5/dt4)
! if(nsps.ge.7680) lag2=nint(1.0/dt4)
! lag1=-lag2
jadd=11
if(nsps.ge.3600) jadd=7
if(nsps.ge.7680) jadd=6
if(nsps.ge.16000) jadd=3
if(nsps.ge.41472) jadd=1
do i=-ia,ia
x=s1(i0+2*mode66+i,:)-s1(i0+i,:) !Do the 2FSK demodulation
! do lag=lag1,lag2
do lag=-15,15
do k=1,22
n=4*NSTEP*(k-1) + 1
j=n+lag+jadd
if(j.ge.1 .and. j.le.jz) sync_sig(i,lag)=sync_sig(i,lag) + sync(n)*x(j)
enddo
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enddo
enddo
ijpk=maxloc(sync_sig)
ii=ijpk(1)-65
jj=ijpk(2)-16
! Use peakup() here?
f0=nfqso + ii*df
jdt=jj
! j0=0.5/dt4
! if(nsps.ge.7680) j0=1.0/dt4
tsym=nsps/12000.0
xdt=jdt*tsym/4.0
snr1=maxval(sync_sig)/22.0
! do i=-64,64
! write(62,3062) nfqso+i*df,sync_sig(i,jj)
!3062 format(2f12.3)
! enddo
! do j=-15,15
! write(63,3063) j,j*dt4,sync_sig(ii,j)
!3063 format(i5,2f12.3)
! enddo
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return
end subroutine sync66