118 lines
3.6 KiB
Plaintext
118 lines
3.6 KiB
Plaintext
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subroutine ccf65(ss,nhsym,ssmax,sync1,dt1,flipk,syncshort,snr2,dt2)
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parameter (NFFT=512,NH=NFFT/2)
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real ss(322) !Input: half-symbol normalized powers
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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 ccf(-11:54)
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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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! 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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! 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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pr2(i)=0.
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k=2*mod((i-1)/8,2)-1
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if(i.le.NH) 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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! Not sure why, but it works significantly better without the following line:
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! pr(j-1)=pr(j)
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enddo
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call four2a(cpr,NFFT,1,-1,0)
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call four2a(cpr2,NFFT,1,-1,0)
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first=.false.
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endif
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! 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 i=1,nhsym-1
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s(i)=min(ssmax,ss(i)+ss(i+1))
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! s(i)=ss(i)+ss(i+1)
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enddo
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call pctile(s,nhsym-1,50,base)
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s(1:nhsym-1)=s(1:nhsym-1)-base
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s(nhsym:NFFT)=0.
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call four2a(cs,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=-11,54 !Check for best JT65 sync
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j=lag
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if(j.lt.1) j=j+NFFT
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ccf(lag)=s(j)
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! if(abs(ccf(lag)).gt.ccfbest) then
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if(ccf(lag).gt.ccfbest) then !No inverted sync for use at HF
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! ccfbest=abs(ccf(lag))
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ccfbest=ccf(lag)
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lagpk=lag
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flipk=1.0
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! if(ccf(lag).lt.0.0) flipk=-1.0
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endif
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enddo
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! do lag=-11,54 !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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! endif
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! enddo
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! Find rms level on baseline of "ccfblue", for normalization.
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sum=0.
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do lag=-11,54
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if(abs(lag-lagpk).gt.1) sum=sum + ccf(lag)
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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=-11,54
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if(abs(lag-lagpk).gt.1) sq=sq + (ccf(lag)-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=lagpk*(2048.0/11025.0) - 2.5
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! Find base level for normalizing snr2.
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do i=1,nhsym
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tmp1(i)=ss(i)
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enddo
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call pctile(tmp1,nhsym,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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dt2=0.
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return
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end subroutine ccf65
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