2012-05-22 17:09:48 +00:00
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subroutine decode1a(dd,newdat,f0,nflip,mode65,nfsample,xpol,
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+ mycall,hiscall,hisgrid,neme,ndepth,nqd,dphi,
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+ nutc,nkhz,ndf,ipol,sync2,a,dt,pol,nkv,nhist,qual,decoded)
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! Apply AFC corrections to a candidate JT65 signal, then decode it.
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parameter (NMAX=60*96000) !Samples per 60 s
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real*4 dd(4,NMAX) !92 MB: raw data from Linrad timf2
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complex cx(NMAX/64), cy(NMAX/64) !Data at 1378.125 samples/s
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complex c5x(NMAX/256),c5y(NMAX/256),c5tmp(NMAX/256) !Data at 344.53125 Hz
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complex c5a(512)
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complex z
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real s2(66,126)
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real s3(64,63),sy(63)
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real a(5)
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logical first,xpol
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character decoded*22
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character mycall*12,hiscall*12,hisgrid*6
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data first/.true./,jjjmin/1000/,jjjmax/-1000/
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data nutc0/-999/,nkhz0/-999/
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save
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! Mix sync tone to baseband, low-pass filter, downsample to 1378.125 Hz
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dt00=dt
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call timer('filbig ',0)
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call filbig(dd,NMAX,f0,newdat,nfsample,xpol,cx,cy,n5)
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! NB: cx, cy have sample rate 96000*77125/5376000 = 1378.125 Hz
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call timer('filbig ',1)
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joff=0
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sqa=0.
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sqb=0.
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do i=1,n5
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sqa=sqa + real(cx(i))**2 + aimag(cx(i))**2
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sqb=sqb + real(cy(i))**2 + aimag(cy(i))**2
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enddo
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sqa=sqa/n5
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sqb=sqb/n5
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! Find best DF, f1, f2, DT, and pol. Start by downsampling to 344.53125 Hz
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z=cmplx(cos(dphi),sin(dphi))
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cy(:n5)=z*cy(:n5) !Adjust for cable length difference
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call timer('fil6521 ',0)
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call fil6521(cx,n5,c5x,n6)
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call fil6521(cy,n5,c5y,n6)
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call timer('fil6521 ',1)
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! Add some zeros at start of c5 arrays -- empirical fix for negative DT's
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! NB: might be better to add zeros to cx and cy, rather than here.
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! Q: is the DT search range big enough?
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nadd=200
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c5tmp(1:nadd)=0.
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c5tmp(1+nadd:n6+nadd)=c5x(1:n6)
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c5x(1:n6+nadd)=c5tmp(1:n6+nadd)
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c5tmp(1+nadd:n6+nadd)=c5y(1:n6)
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c5y(1:n6+nadd)=c5tmp(1:n6+nadd)
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n6=n6+nadd
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fsample=1378.125/4.
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a(5)=dt00
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i0=nint((a(5)+0.5)*fsample) - 2 + 200
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if(i0.lt.1) then
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write(13,*) 'i0 too small in decode1a:',i0,f0
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flush(13)
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i0=1
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endif
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nz=n6+1-i0
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! We're looking only at sync tone here... so why not downsample by another
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! factor of 1/8, say? Should be a significant execution speed-up.
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call timer('afc65b ',0)
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! Best fit for DF, f1, f2, pol
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call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,xpol,a,
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+ ccfbest,dtbest)
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call timer('afc65b ',1)
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pol=a(4)/57.2957795
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aa=cos(pol)
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bb=sin(pol)
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sq0=aa*aa*sqa + bb*bb*sqb
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sync2=3.7*ccfbest/sq0
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! Apply AFC corrections to the time-domain signal
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! Now we are back to using the 1378.125 Hz sample rate, enough to
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! accommodate the full JT65C bandwidth.
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call timer('twkfreq ',0)
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call twkfreq(cx,cy,n5,a)
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call timer('twkfreq ',1)
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! Compute spectrum at best polarization for each half symbol.
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! Adding or subtracting a small number (e.g., 5) to j may make it decode.\
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! NB: might want to try computing full-symbol spectra (nfft=512, even for
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! submodes B and C).
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nsym=126
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nfft=512/mode65
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j=(dt00+dtbest+2.685)*1378.125 + joff
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if(j.lt.0) j=0
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call timer('sh_ffts ',0)
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! Perhaps should try full-symbol-length FFTs even in B, C sub-modes?
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! (Tried this, found no significant difference in decodes.)
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do k=1,nsym
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do n=1,mode65
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do i=1,nfft
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j=j+1
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c5a(i)=aa*cx(j) + bb*cy(j)
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enddo
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call four2a(c5a,nfft,1,1,1)
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if(n.eq.1) then
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do i=1,66
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s2(i,k)=real(c5a(i))**2 + aimag(c5a(i))**2
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enddo
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else
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do i=1,66
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s2(i,k)=s2(i,k) + real(c5a(i))**2 + aimag(c5a(i))**2
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enddo
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endif
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enddo
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enddo
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call timer('sh_ffts ',1)
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flip=nflip
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call timer('dec65b ',0)
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call decode65b(s2,flip,mycall,hiscall,hisgrid,mode65,neme,ndepth,
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+ nqd,nkv,nhist,qual,decoded,s3,sy)
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dt=dt00 + dtbest
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call timer('dec65b ',1)
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if(nqd.eq.1 .and. nkv.eq.0) then
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if(nutc.ne.nutc0) syncbest=0.
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if(sync2.gt.syncbest) then
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if(nutc.eq.nutc0) nsave=nsave-1
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if(nkhz.ne.nkhz0) nsave=0
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nkhz0=nkhz
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nsave=min(32,nsave+1)
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npol=nint(57.296*pol)
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call s3avg(nsave,mode65,nutc,ndf,dt+0.8,npol,s3,nkv,decoded)
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syncbest=sync2
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endif
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nutc0=nutc
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endif
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return
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end
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