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50 lines
1.3 KiB
Fortran
50 lines
1.3 KiB
Fortran
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subroutine xcor4(s2,ipk,nsteps,nsym,ich,mode4)
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! Computes ccf of the 4-FSK spectral array s2 and the pseudo-random
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! array pr2. Returns peak of CCF and the lag at which peak occurs.
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! The CCF peak may be either positive or negative, with negative
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! implying a message with report.
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use jt4
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parameter (NHMAX=1260) !Max length of power spectra
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parameter (NSMAX=525) !Max number of half-symbol steps
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real s2(NHMAX,NSMAX) !2d spectrum, stepped by half-symbols
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real a(NSMAX)
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save
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nw=nch(ich)
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do j=1,nsteps
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n=2*mode4
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if(mode4.eq.1) then
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a(j)=max(s2(ipk+n,j),s2(ipk+3*n,j)) - max(s2(ipk ,j),s2(ipk+2*n,j))
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else
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kz=max(1,nw/2)
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ss0=0.
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ss1=0.
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ss2=0.
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ss3=0.
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wsum=0.
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do k=-kz+1,kz-1
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w=float(kz-iabs(k))/nw
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wsum=wsum+w
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ss0=ss0 + w*s2(ipk +k,j)
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ss1=ss1 + w*s2(ipk+ n+k,j)
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ss2=ss2 + w*s2(ipk+2*n+k,j)
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ss3=ss3 + w*s2(ipk+3*n+k,j)
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enddo
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a(j)=(max(ss1,ss3) - max(ss0,ss2))/sqrt(wsum)
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endif
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enddo
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do lag=1,65
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x=0.
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do i=1,nsym
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j=2*i-1+lag
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if(j.ge.1 .and. j.le.nsteps) x=x+a(j)*float(2*npr(i)-1)
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enddo
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zz(ipk,lag,ich)=x
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enddo
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return
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end subroutine xcor4
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