subroutine decoder(ss,c0)

! Decoder for JT9.

  parameter (NMAX=1800*12000)        !Total sample intervals per 30 minutes
  parameter (NDMAX=1800*1500)        !Sample intervals at 1500 Hz rate
  parameter (NSMAX=22000)            !Max length of saved spectra
  real ss(184,NSMAX)
  character*22 msg
  character*33 line
  character*80 fmt
  character*20 datetime
  real*4 ccfred(NSMAX)
  logical ccfok(NSMAX)
  integer*1 i1SoftSymbols(207)
  integer*2 id2
  integer ii(1)
  complex c0(NDMAX)
  complex c1(NDMAX)
  common/npar/nutc,ndiskdat,ntrperiod,nfqso,newdat,npts8,nfa,nfb,ntol,  &
       kin,nzhsym,nsave,nagain,ndepth,nrxlog,nfsample,datetime
  common/tracer/limtrace,lu
  save

  call timer('decoder ',0)

  open(13,file='decoded.txt',status='unknown')
  ntrMinutes=ntrperiod/60
  newdat=1
  nsynced=0
  ndecoded=0
  limit=5000
  ccflim=4.0
  if(ndepth.ge.2) then
     limit=50000
     ccflim=3.0
  endif
  if(ndepth.ge.3) then
     limit=200000
     ccflim=2.5
  endif

  nsps=0
  if(ntrMinutes.eq.1) then
     nsps=6912
     df3=1500.0/2048.0
     fmt='(i4.4,i4,i5,f6.1,f8.0,i4,3x,a22)'
  else if(ntrMinutes.eq.2) then
     nsps=15360
     df3=1500.0/2048.0
     fmt='(i4.4,i4,i5,f6.1,f8.1,i4,3x,a22)'
  else if(ntrMinutes.eq.5) then
     nsps=40960
     df3=1500.0/6144.0
     fmt='(i4.4,i4,i5,f6.1,f8.1,i4,3x,a22)' 
 else if(ntrMinutes.eq.10) then
     nsps=82944
     df3=1500.0/12288.0
     fmt='(i4.4,i4,i5,f6.1,f8.2,i4,3x,a22)'
  else if(ntrMinutes.eq.30) then
     nsps=252000
     df3=1500.0/32768.0
     fmt='(i4.4,i4,i5,f6.1,f8.2,i4,3x,a22)'
  endif
  if(nsps.eq.0) stop 'Error: bad TRperiod'    !Better: return an error code###

  kstep=nsps/2
  tstep=kstep/12000.0
  idf=ntol/df3 + 0.999

  do nqd=1,0,-1
     if(nqd.eq.1) then
        nfa1=nfqso-ntol
        nfb1=nfqso+ntol
     else
        nfa1=nfa
        nfb1=nfb
     endif
     call timer('sync9   ',0)
! Compute ccfred()
     call sync9(ss,nzhsym,tstep,df3,nfa1,nfb1,ntol,nfqso,ccfred,ia,ib,ipk)
     call timer('sync9   ',1)

     ccfok=.false.
     ccfok(max(ipk-idf,1):min(ipk+idf,NSMAX))=.true.
     if(nqd.eq.1) then
        ia1=ia
        ib1=ib
     else
        do i=ia+9,ib-25
           t1=ccfred(i)/(sum(ccfred(i-8:i-6)/3.0))
           t2=ccfred(i)/(sum(ccfred(i+23:i+25)/3.0))
           if(t1.ge.ccflim .and. t2.ge.ccflim) ccfok(i)=.true.
        enddo
        ccfok(ia1:ib1)=.false.
     endif

     nRxLog=0
     fgood=0.
     nsps8=nsps/8
     df8=1500.0/nsps8
     sbest=-1.0
     dblim=db(864.0/nsps8) - 26.2
     i1=max(nint((nfqso-1000)/df3 - 10),ia)
     i2=min(nint((nfqso-1000)/df3 + 10),ib)
     ii=maxloc(ccfred(i1:i2))
     i00=ii(1) + i1 - 1

     do i=ia,ib
        f=(i-1)*df3
        if(.not.ccfok(i)) cycle
        if(nqd.eq.1 .or.                                                  &
           (ccfred(i).ge.3.0 .and. abs(f-fgood).gt.10.0*df8)) then
           call timer('decode9a',0)
           fpk=1000.0 + df3*(i-1)
           c1(1:npts8)=conjg(c0(1:npts8))
           call decode9a(c1,npts8,nsps8,fpk,syncpk,snrdb,xdt,freq,drift,   &
                i1SoftSymbols)
           call timer('decode9a',1)

           call timer('decode9 ',0)
           call decode9(i1SoftSymbols,limit,nlim,msg)
           call timer('decode9 ',1)
 
           sync=(syncpk+1)/4.0
           if(sync.lt.0.0 .or. snrdb.lt.dblim-2.0) sync=0.0
           nsync=sync
           if(nsync.gt.10) nsync=10
           nsnr=nint(snrdb)
           ndrift=nint(drift/df3)
           if(msg.ne.'                      ') then
              write(*,fmt) nutc,nsync,nsnr,xdt,freq,ndrift,msg
              write(13,fmt) nutc,nsync,nsnr,xdt,freq,ndrift,msg
              fgood=f
              nsynced=1
              ndecoded=1
              ccfok(max(ia,i-3):min(ib,i+11))=.false.
              call flush(6)
           endif
        endif
     enddo
     call flush(6)
     if(nagain.ne.0) exit
  enddo

  write(*,1010) nsynced,ndecoded
1010 format('<DecodeFinished>',2i4)
  call flush(6)
  close(13)

  call timer('decoder ',1)
  if(nstandalone.eq.0) call timer('decoder ',101)

  return
end subroutine decoder