186 lines
4.6 KiB
Plaintext
186 lines
4.6 KiB
Plaintext
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subroutine synciscat(cdat,npts,nh,npct,s0,jsym,df,ntol,NFreeze, &
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MouseDF,mousebutton,mode4,nafc,psavg,xsync,sig,ndf0,msglen, &
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ipk,jpk,idf,df1)
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! Synchronize an ISCAT signal
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! cdat() is the downsampled analytic signal.
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! Sample rate = fsample = BW = 11025 * (9/32) = 3100.78125 Hz
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! npts, nsps, etc., are all reduced by 9/32
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parameter (NMAX=30*3101)
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parameter (NSZ=4*1400)
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complex cdat(NMAX)
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complex c(288)
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real s0(288,NSZ)
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real fs0(288,96) !108 = 96 + 3*4
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real savg(288)
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real sref(288)
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real psavg(72) !Average spectrum of whole file
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integer icos(4)
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data icos/0,1,3,2/
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data nsync/4/,nlen/2/,ndat/18/
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! Silence compiler warnings:
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sigbest=-20.0
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ndf0best=0
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msglenbest=0
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ipkbest=0
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jpkbest=0
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ipk2=0
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idfbest=mousebutton
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fsample=3100.78125 !New sample rate
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nsps=144/mode4
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nsym=npts/nsps - 1
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nblk=nsync+nlen+ndat
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nfft=2*nsps !FFTs at twice the symbol length,
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kstep=nsps/4 ! stepped by 1/4 symbol
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df=fsample/nfft
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fac=1.0/1000.0 !Somewhat arbitrary
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savg=0.
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s0=0.
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ia=1-kstep
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do j=1,4*nsym !Compute symbol spectra
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ia=ia+kstep
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ib=ia+nsps-1
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if(ib.gt.npts) exit
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c(1:nsps)=fac*cdat(ia:ib)
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c(nsps+1:nfft)=0.
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call four2a(c,nfft,1,-1,1)
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do i=1,nfft
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s0(i,j)=real(c(i))**2 + aimag(c(i))**2
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savg(i)=savg(i) + s0(i,j) !Accumulate avg spectrum
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enddo
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i0=40
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enddo
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jsym=4*nsym
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savg=savg/jsym
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do i=1,71 !Compute spectrum in dB, for plot
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if(mode4.eq.1) then
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psavg(i)=2*db(savg(4*i)+savg(4*i-1)+savg(4*i-2)+savg(4*i-3)) + 1.0
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else
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psavg(i)=2*db(savg(2*i)+savg(2*i-1)) + 7.0
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endif
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enddo
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do i=nh+1,nfft-nh
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call pctile(savg(i-nh),2*nh+1,npct,sref(i))
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enddo
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sref(1:nh)=sref(nh+11)
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sref(nfft-nh+1:nfft)=sref(nfft-nh)
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do i=1,nfft !Normalize the symbol spectra
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fac=1.0/sref(i)
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if(i.lt.11) fac=1.0/savg(11)
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do j=1,jsym
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s0(i,j)=fac*s0(i,j)
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enddo
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enddo
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nfold=jsym/96
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jb=96*nfold
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ttot=npts/fsample !Length of record (s)
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df1=df/ttot !Step size for f1=fdot
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idf1=-25.0/df1
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idf2=5.0/df1
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if(nafc.eq.0) then
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idf1=0
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idf2=0
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else if(mod(-idf1,2).eq.1) then
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idf1=idf1-1
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endif
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xsyncbest=0.
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do idf=idf1,idf2 !Loop over fdot
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fs0=0.
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do j=1,jb !Fold s0 into fs0, modulo 4*nblk
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k=mod(j-1,4*nblk)+1
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ii=nint(idf*float(j-jb/2)/float(jb))
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ia=max(1-ii,1)
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ib=min(nfft-ii,nfft)
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do i=ia,ib
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fs0(i,k)=fs0(i,k) + s0(i+ii,j)
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enddo
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enddo
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ref=nfold*4
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i0=27
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if(mode4.eq.1) i0=95
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ia=i0-nint(ntol/df)
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ib=i0+nint(ntol/df)
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if(ia.lt.1) ia=1
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if(ib.gt.nfft-3) ib=nfft-3
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smax=0.
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ipk=1
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jpk=1
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do j=0,4*nblk-1 !Find sync pattern: lags 0-95
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do i=ia,ib !Search specified freq range
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ss=0.
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do n=1,4 !Sum over 4 sync tones
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k=j+4*n-3
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if(k.gt.96) k=k-96
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ss=ss + fs0(i+2*icos(n),k)
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enddo
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if(ss.gt.smax) then
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smax=ss
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ipk=i !Frequency offset, DF
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jpk=j+1 !Time offset, DT
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endif
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enddo
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enddo
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xsync=smax/ref - 1.0
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if(nfold.lt.26) xsync=xsync * sqrt(nfold/26.0)
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xsync=xsync-0.5 !Empirical
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sig=db(smax/ref - 1.0) - 15.0
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if(mode4.eq.1) sig=sig-5.0
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! if(sig.lt.-20 .or. xsync.lt.1.0) sig=-20.0
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! if(sig.lt.-20) sig=-20.0
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ndf0=nint(df*(ipk-i0))
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smax=0.
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ja=jpk+16
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if(ja.gt.4*nblk) ja=ja-4*nblk
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jj=jpk+20
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if(jj.gt.4*nblk) jj=jj-4*nblk
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do i=ipk,ipk+60,2 !Find User's message length
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ss=fs0(i,ja) + fs0(i+10,jj)
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if(ss.gt.smax) then
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smax=ss
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ipk2=i
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endif
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enddo
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msglen=(ipk2-ipk)/2
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if(msglen.lt.2 .or. msglen.gt.29) cycle
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if(xsync.ge.xsyncbest) then
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xsyncbest=xsync
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sigbest=sig
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ndf0best=ndf0
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msglenbest=msglen
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ipkbest=ipk
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jpkbest=jpk
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idfbest=idf
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endif
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enddo
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xsync=xsyncbest
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sig=sigbest
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ndf0=ndf0best
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msglen=msglenbest
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ipk=ipkbest
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jpk=jpkbest
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idf=idfbest
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if(nafc.eq.0) idf=0
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return
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end subroutine synciscat
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