subroutine decode4(dat,npts,dtx,nfreq,flip,mode4,ndepth,neme,minw, & mycall,hiscall,hisgrid,decoded,nfano,deepbest,qbest,ichbest) ! Decodes JT4 data, assuming that DT and DF have already been determined. ! Input dat(npts) has already been downsampled by 2: rate = 11025/2. ! ### NB: this initial downsampling should be removed in WSJT-X, since ! it restricts the useful bandwidth to < 2.7 kHz. use jt4 real dat(npts) !Raw data character decoded*22,deepmsg*22,deepbest*22 character*12 mycall,hiscall character*6 hisgrid real*8 dt,df,phi,f0,dphi,twopi,phi1,dphi1 complex*16 cz,cz1,c0,c1 real*4 sym(207) twopi=8*atan(1.d0) dt=2.d0/11025 !Sample interval (2x downsampled data) df=11025.d0/2520.d0 !Tone separation for JT4A mode nsym=206 amp=15.0 istart=nint((dtx+0.8)/dt) !Start index for synced FFTs if(istart.lt.0) istart=0 nchips=0 qbest=0. qtop=0. deepmsg=' ' ichbest=-1 c0=0. k=istart phi=0.d0 phi1=0.d0 ich1=minw+1 do ich=1,7 if(nch(ich).le.mode4) ich2=ich enddo do ich=ich1,ich2 nchips=min(nch(ich),70) nspchip=1260/nchips k=istart phi=0.d0 phi1=0.d0 fac2=1.e-8 * sqrt(float(mode4)) do j=1,nsym+1 if(flip.gt.0.0) then f0=nfreq + (npr(j))*mode4*df f1=nfreq + (2+npr(j))*mode4*df else f0=nfreq + (1-npr(j))*mode4*df f1=nfreq + (3-npr(j))*mode4*df endif dphi=twopi*dt*f0 dphi1=twopi*dt*f1 sq0=0. sq1=0. do nc=1,nchips phi=0.d0 phi1=0.d0 c0=0. c1=0. do i=1,nspchip k=k+1 phi=phi+dphi phi1=phi1+dphi1 cz=dcmplx(cos(phi),-sin(phi)) cz1=dcmplx(cos(phi1),-sin(phi1)) if(k.le.npts) then c0=c0 + dat(k)*cz c1=c1 + dat(k)*cz1 endif enddo sq0=sq0 + real(c0)**2 + aimag(c0)**2 sq1=sq1 + real(c1)**2 + aimag(c1)**2 enddo sq0=fac2*sq0 sq1=fac2*sq1 rsym=amp*(sq1-sq0) if(j.ge.1) then rsymbol(j,ich)=rsym sym(j)=rsym endif enddo call extract4(sym,ncount,decoded) !Do the convolutional decode nfano=0 if(ncount.ge.0) then nfano=1 ichbest=ich exit endif qual=0. !Now try deep search if(ndepth.ge.1) then call deep4(sym(2),neme,flip,mycall,hiscall,hisgrid,deepmsg,qual) if(qual.gt.qbest) then qbest=qual deepbest=deepmsg ichbest=ich endif endif enddo if(qbest.gt.qtop) then qtop=qbest endif qual=qbest return end subroutine decode4