mirror of https://github.com/saitohirga/WSJT-X.git
96 lines
2.7 KiB
Fortran
96 lines
2.7 KiB
Fortran
subroutine decode65a(dd,npts,newdat,f0,nflip,mode65,sync2,a,dt, &
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nbmkv,nhist,decoded)
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! Apply AFC corrections to a candidate JT65 signal, then decode it.
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parameter (NMAX=60*12000) !Samples per 60 s
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real*4 dd(NMAX) !92 MB: raw data from Linrad timf2
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complex cx(NMAX/8) !Data at 1378.125 samples/s
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complex c5x(NMAX/32) !Data at 344.53125 Hz
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complex c5a(512)
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real s2(66,126)
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real a(5)
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logical first
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character decoded*22
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data first/.true./,jjjmin/1000/,jjjmax/-1000/
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data nhz0/-9999999/
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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,npts,f0,newdat,cx,n5,sq0)
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call timer('filbig ',1)
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! NB: cx has sample rate 12000*77125/672000 = 1378.125 Hz
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! Find best DF, f1, f2, and DT. Start by downsampling to 344.53125 Hz
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call timer('fil6521 ',0)
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! Add some zeros at start of c5 arrays -- empirical fix for negative DT's
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nadd=1089
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c5x(:nadd)=0.
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call fil6521(cx,n5,c5x(nadd+1),n6)
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n6=n6+nadd
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call timer('fil6521 ',1)
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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 + nadd
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if(i0.lt.1) then
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! write(23,*) 'i0 too small in decode1a:',i0,f0,a(5),fsample,nadd
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! flush(23)
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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, and f2
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call afc65b(c5x(i0),nz,fsample,nflip,a,ccfbest,dtbest)
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call timer('afc65b ',1)
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sync2=3.7e-4*ccfbest/sq0 !Constant is empirical
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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 twkfreq65(cx,n5,a)
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call timer('twkfreq ',1)
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! Compute spectrum 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
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j=(dt00+dtbest+2.685)*1378.125
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if(j.lt.0) j=0
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call timer('sh_ffts ',0)
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do k=1,nsym
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do i=1,nfft
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j=j+1
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c5a(i)=cx(j)
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enddo
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call four2a(c5a,nfft,1,1,1)
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do i=1,66
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jj=i
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if(mode65.eq.2) jj=2*i-1
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if(mode65.eq.4) jj=4*i-3
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s2(i,k)=real(c5a(jj))**2 + aimag(c5a(jj))**2
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enddo
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enddo
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call timer('sh_ffts ',1)
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call timer('dec65b ',0)
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call decode65b(s2,nflip,mode65,nbmkv,nhist,decoded)
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dt=dt00 + dtbest + 1.7
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call timer('dec65b ',1)
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return
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end subroutine decode65a
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