mirror of https://github.com/saitohirga/WSJT-X.git
70 lines
1.7 KiB
Fortran
70 lines
1.7 KiB
Fortran
subroutine synct(data,jz,jstart,f0,smax)
|
|
|
|
C Gets a refined value of jstart.
|
|
|
|
parameter (NMAX=30*11025)
|
|
parameter (NB3=3*512)
|
|
real data(jz)
|
|
real*8 dpha,twopi
|
|
complex*16 z,dz
|
|
complex c,c1,zz
|
|
common/hcom/c(NMAX)
|
|
|
|
ps(zz)=real(zz)**2 + imag(zz)**2 !Power spectrum function
|
|
|
|
C Convert data to baseband (complex result) using quadrature LO.
|
|
twopi=8*atan(1.d0)
|
|
dpha=twopi*f0/11025.d0
|
|
dz=cmplx(cos(dpha),-sin(dpha))
|
|
z=1.d0/dz
|
|
do i=1,jz
|
|
z=z*dz
|
|
c(i)=data(i)*z
|
|
enddo
|
|
|
|
C Detect zero-beat sync tone in 512-sample chunks, stepped by 1.
|
|
C Sums replace original values in c(i).
|
|
|
|
zz=0
|
|
do i=1,512 !Compute first sum
|
|
zz=zz+c(i)
|
|
enddo
|
|
c1=c(1)
|
|
c(1)=zz
|
|
do i=2,jz-512 !Compute the rest recursively
|
|
zz=c(i-1)+c(i+511)-c1
|
|
c1=c(i) !Save original value
|
|
c(i)=zz !Save the sum
|
|
enddo
|
|
|
|
C Iterate to find the best jstart.
|
|
jstart=jstart+NB3
|
|
nz=(jz-jstart)/NB3 -1
|
|
smax=0.
|
|
jstep=256
|
|
jbest=jstart
|
|
|
|
10 jstep=jstep/2
|
|
jstart=jbest
|
|
do j=jstart-jstep,jstart+jstep,jstep
|
|
s=0.
|
|
r=0.
|
|
do n=1,nz
|
|
k=(n-1)*NB3 + j
|
|
s=s + ps(c(k))
|
|
r=r + ps(c(k+512)) + ps(c(k+1024))
|
|
enddo
|
|
s=2*s/r !Better to use s/r or s-r?
|
|
if(s.gt.smax) then
|
|
smax=s
|
|
jbest=j
|
|
endif
|
|
enddo
|
|
if(jstep.gt.1) go to 10
|
|
|
|
jstart=jbest
|
|
if(jstart.gt.NB3) jstart=jstart-NB3
|
|
|
|
return
|
|
end
|