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57 lines
1.6 KiB
Fortran
57 lines
1.6 KiB
Fortran
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subroutine lenmsk(r,npts,msglen)
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! Determine length of the user message in a JTMS ping.
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real r(60000)
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real acf(4872)
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integer np(9)
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data np/5,7,9,11,13,17,19,23,29/ !Permissible message lengths
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save acf !Why necessary? (But don't remove!)
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msglen=0 !Use ACF to find msg length
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if(npts.ge.8*168) then
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r=r-sum(r(1:npts))/npts
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acfmax=0.
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acf0=dot_product(r(1:npts),r(1:npts))
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kz=min(nint(0.75*npts),29*168)
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do k=8,kz
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fac=float(npts)/(npts-k)
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acf(k)=fac*dot_product(r(1:npts),r(1+k:npts+k))/acf0
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enddo
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call hipass(acf(8),kz-7,50)
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do k=8,kz !Find acfmax, kpk
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if(acf(k).gt.acfmax) then
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acfmax=acf(k)
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kpk=k
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endif
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enddo
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sumsq=0.
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n=0
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do k=8,kz !Find rms, skipping around kpk
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if(abs(k-kpk).gt.10) then
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sumsq=sumsq+acf(k)**2
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n=n+1
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endif
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enddo
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rms=sqrt(sumsq/n)
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acf=acf/rms !Normalize the acf
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amax2=0.
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acflim=3.5
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do i=1,9
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k=168*np(i) !Check only the permitted lengths
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if(k.gt.kz) go to 10
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if(acf(k).gt.acflim .and. acf(k).gt.amax2) then
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amax2=acf(k) !Save best value >3.5 sigma
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msglen=np(i) !Save message length
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kpk2=k
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endif
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enddo
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10 continue
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endif
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return
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end subroutine lenmsk
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