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https://github.com/saitohirga/WSJT-X.git
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52 lines
1.5 KiB
FortranFixed
52 lines
1.5 KiB
FortranFixed
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subroutine syncf0(data,jz,NTol,jstart,f0,smax)
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C Does 512-pt FFTs of data with 256-pt step size.
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C Finds sync tone and determines aproximate values for jstart and f0.
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real data(jz) !Raw data
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real s2(128,6) !Average spectra at half-symbol spacings
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real x(512)
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complex cx(0:511)
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complex z
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equivalence (x,cx)
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ps(z)=real(z)**2 + imag(z)**2 !Power spectrum function
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call zero(s2,6*128) !Clear average
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df=11025./512.
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ia=(1076-NTol)/df
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ib=(1076+Ntol)/df
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nblk=jz/256 - 6
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C Most of the time in this routine is in this loop.
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do n=1,nblk !Accumulate avg spectrum for
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j=256*(n-1)+1 !512-pt blocks, stepping by 256
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call move(data(j),x,512)
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call xfft(x,512)
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do i=ia,ib
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x(i)=ps(cx(i))
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enddo
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k=mod(n-1,6)+1
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call add(s2(ia,k),x(ia),s2(ia,k),ib-ia+1) !Average at each step
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enddo
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C Look for best spectral peak, using the "sync off" phases as reference.
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smax=0.
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do i=ia,ib
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do k=1,6
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k1=mod(k+1,6)+1
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k2=mod(k+3,6)+1
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r=0.5*(s2(i,k1)+s2(i,k2))
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s=s2(i,k)/r
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if(s.gt.smax) then
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smax=s
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jstart=(k-1)*256 + 1 !Best starting place for sync
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f0=i*df !Best sync frequency
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endif
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enddo
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enddo
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return
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end
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