2015-04-22 13:48:03 -04:00
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subroutine decode4(dat,npts,dtx,nfreq,flip,mode4,ndepth,neme,minw, &
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mycall,hiscall,hisgrid,decoded,nfano,deepbest,qbest,ichbest)
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! Decodes JT4 data, assuming that DT and DF have already been determined.
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! Input dat(npts) has already been downsampled by 2: rate = 11025/2.
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! ### NB: this initial downsampling should be removed in WSJT-X, since
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! it restricts the useful bandwidth to < 2.7 kHz.
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use jt4
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real dat(npts) !Raw data
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character decoded*22,deepmsg*22,deepbest*22
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character*12 mycall,hiscall
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character*6 hisgrid
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real*8 dt,df,phi,f0,dphi,twopi,phi1,dphi1
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complex*16 cz,cz1,c0,c1
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real*4 sym(207)
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twopi=8*atan(1.d0)
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dt=2.d0/11025 !Sample interval (2x downsampled data)
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df=11025.d0/2520.d0 !Tone separation for JT4A mode
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nsym=206
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amp=15.0
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istart=nint((dtx+0.8)/dt) !Start index for synced FFTs
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if(istart.lt.0) istart=0
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nchips=0
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2015-05-27 09:08:28 -04:00
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qbest=0.
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qtop=0.
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2015-04-22 13:48:03 -04:00
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deepmsg=' '
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ichbest=-1
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c0=0.
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k=istart
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phi=0.d0
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phi1=0.d0
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ich1=minw+1
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do ich=1,7
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if(nch(ich).le.mode4) ich2=ich
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enddo
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do ich=ich1,ich2
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nchips=nch(ich)
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nspchip=1260/nchips
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k=istart
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phi=0.d0
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phi1=0.d0
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fac2=1.e-8 * sqrt(float(mode4))
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do j=1,nsym+1
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if(flip.gt.0.0) then
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f0=nfreq + (npr(j))*mode4*df
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f1=nfreq + (2+npr(j))*mode4*df
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else
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f0=nfreq + (1-npr(j))*mode4*df
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f1=nfreq + (3-npr(j))*mode4*df
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endif
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dphi=twopi*dt*f0
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dphi1=twopi*dt*f1
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sq0=0.
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sq1=0.
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do nc=1,nchips
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phi=0.d0
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phi1=0.d0
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c0=0.
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c1=0.
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do i=1,nspchip
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k=k+1
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phi=phi+dphi
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phi1=phi1+dphi1
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cz=dcmplx(cos(phi),-sin(phi))
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cz1=dcmplx(cos(phi1),-sin(phi1))
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if(k.le.npts) then
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c0=c0 + dat(k)*cz
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c1=c1 + dat(k)*cz1
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endif
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enddo
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sq0=sq0 + real(c0)**2 + aimag(c0)**2
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sq1=sq1 + real(c1)**2 + aimag(c1)**2
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enddo
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sq0=fac2*sq0
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sq1=fac2*sq1
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rsym=amp*(sq1-sq0)
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if(j.ge.1) then
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rsymbol(j,ich)=rsym
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sym(j)=rsym
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endif
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enddo
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call extract4(sym,ncount,decoded) !Do the convolutional decode
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nfano=0
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if(ncount.ge.0) then
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nfano=1
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ichbest=ich
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exit
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endif
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qual=0. !Now try deep search
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if(ndepth.ge.1) then
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call deep4(sym(2),neme,flip,mycall,hiscall,hisgrid,deepmsg,qual)
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if(qual.gt.qbest) then
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qbest=qual
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deepbest=deepmsg
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ichbest=ich
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endif
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endif
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enddo
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if(qbest.gt.qtop) then
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qtop=qbest
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endif
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qual=qbest
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return
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end subroutine decode4
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