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https://github.com/saitohirga/WSJT-X.git
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c26d0b4f29
Divide DT search range into 3 segments. Search central segment (near DT=0) first and try to decode the largest peak. Then find the largest peak in each of the surrounding segments and try to decode those only if the peak is larger than the one found in the central segment. Also re-indent ft4_decode.f90 and some other minor tweaks.
97 lines
2.6 KiB
Fortran
97 lines
2.6 KiB
Fortran
subroutine sync4d(cd0,i0,ctwk,itwk,sync)
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! Compute sync power for a complex, downsampled FT4 signal.
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include 'ft4_params.f90'
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parameter(NP=NMAX/NDOWN,NSS=NSPS/NDOWN)
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complex cd0(0:NP-1)
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complex csynca(2*NSS),csyncb(2*NSS),csyncc(2*NSS),csyncd(2*NSS)
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complex csync2(2*NSS)
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complex ctwk(2*NSS)
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complex z1,z2,z3,z4
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logical first
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integer icos4a(0:3),icos4b(0:3),icos4c(0:3),icos4d(0:3)
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data icos4a/0,1,3,2/
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data icos4b/1,0,2,3/
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data icos4c/2,3,1,0/
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data icos4d/3,2,0,1/
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data first/.true./
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save first,twopi,csynca,csyncb,csyncc,csyncd,fac
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p(z1)=(real(z1*fac)**2 + aimag(z1*fac)**2)**0.5 !Statement function for power
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if( first ) then
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twopi=8.0*atan(1.0)
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k=1
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phia=0.0
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phib=0.0
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phic=0.0
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phid=0.0
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do i=0,3
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dphia=2*twopi*icos4a(i)/real(NSS)
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dphib=2*twopi*icos4b(i)/real(NSS)
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dphic=2*twopi*icos4c(i)/real(NSS)
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dphid=2*twopi*icos4d(i)/real(NSS)
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do j=1,NSS/2
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csynca(k)=cmplx(cos(phia),sin(phia))
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csyncb(k)=cmplx(cos(phib),sin(phib))
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csyncc(k)=cmplx(cos(phic),sin(phic))
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csyncd(k)=cmplx(cos(phid),sin(phid))
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phia=mod(phia+dphia,twopi)
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phib=mod(phib+dphib,twopi)
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phic=mod(phic+dphic,twopi)
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phid=mod(phid+dphid,twopi)
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k=k+1
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enddo
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enddo
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first=.false.
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fac=1.0/(2.0*NSS)
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endif
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i1=i0 !four Costas arrays
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i2=i0+33*NSS
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i3=i0+66*NSS
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i4=i0+99*NSS
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z1=0.
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z2=0.
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z3=0.
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z4=0.
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if(itwk.eq.1) csync2=ctwk*csynca !Tweak the frequency
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z1=0.
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if(i1.ge.0 .and. i1+4*NSS-1.le.NP-1) then
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z1=sum(cd0(i1:i1+4*NSS-1:2)*conjg(csync2))
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elseif( i1.lt.0 ) then
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npts=(i1+4*NSS-1)/2
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if(npts.le.16) then
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z1=0.
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else
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z1=sum(cd0(0:i1+4*NSS-1:2)*conjg(csync2(2*NSS-npts:)))
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endif
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endif
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if(itwk.eq.1) csync2=ctwk*csyncb !Tweak the frequency
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if(i2.ge.0 .and. i2+4*NSS-1.le.NP-1) z2=sum(cd0(i2:i2+4*NSS-1:2)*conjg(csync2))
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if(itwk.eq.1) csync2=ctwk*csyncc !Tweak the frequency
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if(i3.ge.0 .and. i3+4*NSS-1.le.NP-1) z3=sum(cd0(i3:i3+4*NSS-1:2)*conjg(csync2))
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if(itwk.eq.1) csync2=ctwk*csyncd !Tweak the frequency
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z4=0.
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if(i4.ge.0 .and. i4+4*NSS-1.le.NP-1) then
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z4=sum(cd0(i4:i4+4*NSS-1:2)*conjg(csync2))
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elseif( i4+4*NSS-1.gt.NP-1 ) then
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npts=(NP-1-i4+1)/2
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if(npts.le.16) then
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z4=0.
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else
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z4=sum(cd0(i4:i4+2*npts-1:2)*conjg(csync2(1:npts)))
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endif
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endif
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sync = p(z1) + p(z2) + p(z3) + p(z4)
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return
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end subroutine sync4d
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