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115 lines
3.8 KiB
FortranFixed
115 lines
3.8 KiB
FortranFixed
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subroutine ccf65(ss,sync1,ipol1,dt1,flipk,syncshort,
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+ snr2,ipol2,dt2)
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parameter (NFFT=512,NH=NFFT/2)
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real ss(4,322) !Input: half-symbol powers, 4 pol'ns
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real s(NFFT) !CCF = ss*pr
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complex cs(0:NH) !Complex FT of s
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real s2(NFFT) !CCF = ss*pr2
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complex cs2(0:NH) !Complex FT of s2
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real pr(NFFT) !JT65 pseudo-random sync pattern
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complex cpr(0:NH) !Complex FT of pr
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real pr2(NFFT) !JT65 shorthand pattern
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complex cpr2(0:NH) !Complex FT of pr2
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real tmp1(322)
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real tmp2(322)
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real ccf(-27:27,4)
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logical first
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integer npr(126)
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data first/.true./
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equivalence (s,cs),(pr,cpr),(s2,cs2),(pr2,cpr2)
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save
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C The JT65 pseudo-random sync pattern:
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data npr/
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+ 1,0,0,1,1,0,0,0,1,1,1,1,1,1,0,1,0,1,0,0,
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+ 0,1,0,1,1,0,0,1,0,0,0,1,1,1,0,0,1,1,1,1,
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+ 0,1,1,0,1,1,1,1,0,0,0,1,1,0,1,0,1,0,1,1,
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+ 0,0,1,1,0,1,0,1,0,1,0,0,1,0,0,0,0,0,0,1,
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+ 1,0,0,0,0,0,0,0,1,1,0,1,0,0,1,0,1,1,0,1,
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+ 0,1,0,1,0,0,1,1,0,0,1,0,0,1,0,0,0,0,1,1,
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+ 1,1,1,1,1,1/
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if(first) then
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C Initialize pr, pr2; compute cpr, cpr2.
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fac=1.0/NFFT
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do i=1,NFFT
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pr(i)=0.
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k=2*mod((i-1)/8,2)-1
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pr2(i)=fac*k
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enddo
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do i=1,126
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j=2*i
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pr(j)=fac*(2*npr(i)-1)
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enddo
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call four2a(pr,NFFT,1,-1,0)
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call four2a(pr2,NFFT,1,-1,0)
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first=.false.
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endif
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C Look for JT65 sync pattern and shorthand square-wave pattern.
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ccfbest=0.
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ccfbest2=0.
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do ip=1,4 !Do all four pol'ns
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do i=1,321
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s(i)=min(4.0,ss(ip,i)+ss(ip,i+1))
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enddo
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do i=322,NFFT
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s(i)=0.
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enddo
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call four2a(s,NFFT,1,-1,0) !Real-to-complex FFT
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do i=0,NH
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cs2(i)=cs(i)*conjg(cpr2(i)) !Mult by complex FFT of pr2
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cs(i)=cs(i)*conjg(cpr(i)) !Mult by complex FFT of pr
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enddo
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call four2a(cs,NFFT,1,1,-1) !Complex-to-real inv-FFT
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call four2a(cs2,NFFT,1,1,-1) !Complex-to-real inv-FFT
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do lag=-27,27 !Check for best JT65 sync
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ccf(lag,ip)=s(lag+28)
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if(abs(ccf(lag,ip)).gt.ccfbest) then
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ccfbest=abs(ccf(lag,ip))
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lagpk=lag
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ipol1=ip
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flipk=1.0
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if(ccf(lag,ip).lt.0.0) flipk=-1.0
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endif
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enddo
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do lag=-8,7 !Check for best shorthand
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ccf2=s2(lag+28)
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if(ccf2.gt.ccfbest2) then
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ccfbest2=ccf2
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lagpk2=lag
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ipol2=ip
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endif
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enddo
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enddo
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C Find rms level on baseline of "ccfblue", for normalization.
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sum=0.
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do lag=-26,26
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if(abs(lag-lagpk).gt.1) sum=sum + ccf(lag,ipol1)
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enddo
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base=sum/50.0
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sq=0.
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do lag=-26,26
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if(abs(lag-lagpk).gt.1) sq=sq + (ccf(lag,ipol1)-base)**2
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enddo
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rms=sqrt(sq/49.0)
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sync1=ccfbest/rms - 4.0
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dt1=2.5 + lagpk*(2048.0/11025.0)
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C Find base level for normalizing snr2.
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do i=1,322
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tmp1(i)=ss(ipol2,i)
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enddo
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call pctile(tmp1,tmp2,322,40,base)
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snr2=0.398107*ccfbest2/base !### empirical
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syncshort=0.5*ccfbest2/rms - 4.0 !### better normalizer than rms?
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dt2=2.5 + lagpk2*(2048.0/11025.0)
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return
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end
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