mirror of
https://github.com/saitohirga/WSJT-X.git
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73 lines
2.0 KiB
FortranFixed
73 lines
2.0 KiB
FortranFixed
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real function fchisq(cx,cy,npts,fsample,nflip,a,ccfmax,dtmax)
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parameter (NMAX=60*96000) !Samples per 60 s
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complex cx(npts),cy(npts)
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real a(5)
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complex w,wstep,za,zb,z
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real ss(2600)
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complex csx(0:NMAX/64),csy(0:NMAX/64)
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data twopi/6.283185307/a1,a2,a3/99.,99.,99./
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save
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baud=11025.0/4096.0
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if(a(1).ne.a1 .or. a(2).ne.a2 .or. a(3).ne.a3) then
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a1=a(1)
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a2=a(2)
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a3=a(3)
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C Mix and integrate the complex X and Y signals
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csx(0)=0.
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csy(0)=0.
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w=1.0
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x0=0.5*(npts+1)
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s=2.0/npts
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do i=1,npts
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x=s*(i-x0)
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if(mod(i,100).eq.1) then
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p2=1.5*x*x - 0.5
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! p3=2.5*(x**3) - 1.5*x
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! p4=4.375*(x**4) - 3.75*(x**2) + 0.375
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dphi=(a(1) + x*a(2) + p2*a(3)) * (twopi/fsample)
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wstep=cmplx(cos(dphi),sin(dphi))
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endif
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w=w*wstep
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csx(i)=csx(i-1) + w*cx(i)
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csy(i)=csy(i-1) + w*cy(i)
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enddo
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endif
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C Compute 1/2-symbol powers at 1/16-symbol steps.
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fac=1.e-4
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pol=a(4)/57.2957795
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aa=cos(pol)
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bb=sin(pol)
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nsps=nint(fsample/baud) !Samples per symbol
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nsph=nsps/2 !Samples per half-symbol
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ndiv=16 !Output ss() steps per symbol
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nout=ndiv*npts/nsps
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dtstep=1.0/(ndiv*baud) !Time per output step
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do i=1,nout
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j=i*nsps/ndiv
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k=j-nsph
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ss(i)=0.
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if(k.ge.1) then
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za=csx(j)-csx(k)
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zb=csy(j)-csy(k)
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z=aa*za + bb*zb
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ss(i)=fac*(real(z)**2 + aimag(z)**2)
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endif
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enddo
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ccfmax=0.
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call ccf2(ss,nout,nflip,ccf,lagpk)
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if(ccf.gt.ccfmax) then
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ccfmax=ccf
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dtmax=lagpk*dtstep
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endif
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fchisq=-ccfmax
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return
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end
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