mirror of
https://github.com/saitohirga/WSJT-X.git
synced 2024-11-08 18:16:02 -05:00
125 lines
3.8 KiB
FortranFixed
125 lines
3.8 KiB
FortranFixed
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subroutine decode1a(id,newdat,nfilt,freq,nflip,ipol,sync2,a,dt,
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+ pol,nkv,nhist,qual,decoded)
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C Apply AFC corrections to a candidate JT65 signal, and then try
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C to decode it.
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parameter (NFFT1=77760,NFFT2=2430)
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parameter (NMAX=60*96000) !Samples per 60 s
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integer*2 id(4,NMAX) !46 MB: raw data from Linrad timf2
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complex c2x(NMAX/4), c2y(NMAX/4) !After 1/4 filter and downsample
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complex c3x(NMAX/16),c3y(NMAX/16) !After 1/16 filter and downsample
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complex c4x(NMAX/64),c4y(NMAX/64) !After 1/64 filter and downsample
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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)
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complex c5a(256), c5b(256)
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real s2(256,126)
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real a(5)
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real*8 samratio
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integer resample
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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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save
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C Mix sync tone to baseband, low-pass filter, and decimate by 64
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dt00=dt
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C If freq=125.0 kHz, f0=48000 Hz.
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f0=1000*(freq-77.0) !Freq of sync tone (0-96000 Hz)
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if(nfilt.eq.1) then
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call filbig(id,NMAX,f0,newdat,cx,cy,n5)
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joff=0
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else
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call fil659(id,NMAX,f0,c2x,c2y,n2) !Pass 1: mix and filter both pol'ns
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call fil658(c2x,n2,c3x,n3) !Pass 2
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call fil658(c2y,n2,c3y,n3)
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call fil658(c3x,n3,c4x,n4) !Pass 3
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call fil658(c3y,n3,c4y,n4)
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joff=-8
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C Resample from 96000/64 = 1500 Hz to 1378.125 Hz
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C Converter type: 0=Best quality sinc (band limited), BW=97%
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C 1=medium quality sinc, BW=90%
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C 2=fastest sinc, BW=80%
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C 3=stepwise (very fast)
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C 4=linear (very fast)
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nconv_type=2 !### test! ###
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nchans=2
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samratio=1378.125d0/1500.d0
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i1=resample(c4x,n4,nconv_type,nchans,samratio,cx,n5)
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i2=resample(c4y,n4,nconv_type,nchans,samratio,cy,n5)
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endif
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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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C Find best DF, f1, f2, DT, and pol
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! a(5)=dt00
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! fsample=1378.125
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! i0=nint((a(5)+0.5)*fsample)
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! if(i0.lt.1) i0=1
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! nz=n5+1-i0
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! call afc65b(cx(i0),cy(i0),nz,fsample,nflip,ipol,a,dt,
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! + ccfbest,dtbest)
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call fil6521(cx,n5,c5x,n6)
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call fil6521(cy,n5,c5y,n6)
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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
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if(i0.lt.1) i0=1
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nz=n6+1-i0
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call afc65b(c5x(i0),c5y(i0),nz,fsample,nflip,ipol,a,dt,
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+ ccfbest,dtbest)
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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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C Apply AFC corrections to the time-domain signal
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call twkfreq(cx,cy,n5,a)
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C Compute spectrum at best polarization for each half symbol.
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C Adding or subtracting a small number (e.g., 5) to j may make it decode.
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nsym=126
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nfft=256
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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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j0=j
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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)=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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do i=1,nfft
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j=j+1
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c5b(i)=aa*cx(j) + bb*cy(j)
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enddo
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call four2a(c5b,nfft,1,1,1)
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do i=1,256
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s2(i,k)=real(c5a(i))**2 + aimag(c5a(i))**2 +
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+ real(c5b(i))**2 + aimag(c5b(i))**2
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enddo
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enddo
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flip=nflip
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call decode65b(s2,flip,nkv,nhist,qual,decoded)
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dt=dt00 + dtbest
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return
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end
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