WSJT-X/syncf0.f
J C Dutton c2ceb42b28 Summary: Merge in linux branch
svn+ssh://svn.berlios.de/svnroot/repos/wsjt/WSJT/branches/linux
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git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/trunk@155 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2006-04-05 20:07:32 +00:00

57 lines
1.6 KiB
Fortran

subroutine syncf0(data,jz,NFreeze,NTol,jstart,f0,smax)
C Does 512-pt FFTs of data with 256-pt step size.
C Finds sync tone and determines aproximate values for jstart and f0.
real data(jz) !Raw data
real s2(128,6) !Average spectra at half-symbol spacings
real x(512)
complex cx(0:511)
complex z
equivalence (x,cx)
ps(z)=real(z)**2 + aimag(z)**2 !Power spectrum function
call zero(s2,6*128) !Clear average
df=11025./512.
ia=(f0-400)/df
ib=(f0+400)/df + 0.999
if(NFreeze.eq.1) then
ia=(f0-NTol)/df
ib=(f0+Ntol)/df + 0.999
endif
C Most of the time in this routine is in this loop.
nblk=jz/256 - 6
do n=1,nblk !Accumulate avg spectrum for
j=256*(n-1)+1 !512-pt blocks, stepping by 256
call move(data(j),x,512)
call xfft(x,512)
do i=ia,ib
x(i)=ps(cx(i))
enddo
k=mod(n-1,6)+1
call add(s2(ia,k),x(ia),s2(ia,k),ib-ia+1) !Average at each step
enddo
C Look for best spectral peak, using the "sync off" phases as reference.
smax=0.
do i=ia,ib
do k=1,6
k1=mod(k+1,6)+1
k2=mod(k+3,6)+1
r=0.5*(s2(i,k1)+s2(i,k2))
s=s2(i,k)/r
if(s.gt.smax) then
smax=s
jstart=(k-1)*256 + 1 !Best starting place for sync
f0=i*df !Best sync frequency
endif
enddo
enddo
return
end