subroutine q65b(nutc,nqd,fcenter,nfcal,nfsample,ikhz,mousedf,ntol,          &
     mycall0,hiscall0,hisgrid,mode_q65,f0,fqso,nkhz_center, newdat,nagain,  &
     max_drift,ndepth,datetime,ndop00,idec)

! This routine provides an interface between QMAP and the Q65 decoder
! in WSJT-X.  All arguments are input data obtained from the QMAP GUI.
! Raw Rx data are available as the 96 kHz complex spectrum ca(MAXFFT1)
! in common/cacb.  Decoded messages are sent back to the GUI.

  use q65_decode
  use timer_module, only: timer

  parameter (MAXFFT1=5376000)              !56*96000
  parameter (MAXFFT2=336000)               !56*6000 (downsampled by 1/16)
  parameter (NMAX=60*12000)
  parameter (RAD=57.2957795)
  integer*2 iwave(60*12000)
  complex ca(MAXFFT1)                      !FFT of raw I/Q data from Linrad
  complex cx(0:MAXFFT2-1),cz(0:MAXFFT2)
  real*8 fcenter,freq0,freq1
  character*12 mycall0,hiscall0
  character*12 mycall,hiscall
  character*6 hisgrid
  character*4 grid4
  character*60 result
  character*20 datetime
  common/decodes/ndecodes,ncand,nQDecoderDone,nWDecoderBusy,              &
       nWTransmitting,result(50)
  common/cacb/ca
  save

  if(mycall0(1:1).ne.' ') mycall=mycall0
  if(hiscall0(1:1).ne.' ') hiscall=hiscall0
  if(hisgrid(1:4).ne.'    ') grid4=hisgrid(1:4)

! Find best frequency from sync_dat, the "orange sync curve".
  df3=96000.0/32768.0
  ipk=(1000.0*f0-1.0)/df3
  nfft1=MAXFFT1
  nfft2=MAXFFT2
  df=96000.0/NFFT1
  if(nfsample.eq.95238) then
     nfft1=5120000
     nfft2=322560
     df=96000.0/nfft1
  endif
  nh=nfft2/2
  f_mouse=1000.0*(fqso+48.0) + mousedf
  k0=nint((ipk*df3-1000.0)/df)
  if(nagain.eq.1) k0=nint((f_mouse-1000.0)/df)

  if(k0.lt.nh .or. k0.gt.MAXFFT1-nfft2+1) go to 900
  fac=1.0/nfft2
  cx(0:nfft2-1)=ca(k0:k0+nfft2-1)
  cx=fac*cx

! Here cx is frequency-domain data around the selected
! QSO frequency, taken from the full-length FFT computed in filbig().
! Values for fsample, nfft1, nfft2, df, and the downsampled data rate
! are as follows:

!  fSample  nfft1       df        nfft2  fDownSampled
!    (Hz)              (Hz)                 (Hz)
!----------------------------------------------------
!   96000  5376000  0.017857143  336000   6000.000

  cz(0:MAXFFT2-1)=cx
  cz(MAXFFT2)=0.
! Roll off below 500 Hz and above 2500 Hz.
  ja=nint(500.0/df)
  jb=nint(2500.0/df)
  do i=0,ja
     r=0.5*(1.0+cos(i*3.14159/ja))
     cz(ja-i)=r*cz(ja-i)
     cz(jb+i)=r*cz(jb+i)
  enddo
 cz(ja+jb+1:)=0.

!Transform to time domain (real), fsample=12000 Hz
  call four2a(cz,2*nfft2,1,1,-1)
  do i=0,nfft2-1
     j=nfft2-1-i
     iwave(2*i+2)=nint(real(cz(j)))       !Note the reversed order!
     iwave(2*i+1)=nint(aimag(cz(j)))
  enddo
  iwave(2*nfft2+1:)=0

  nsubmode=mode_q65-1
  nfa=990                   !Tight limits around ipk for the wideband decode
  nfb=1010
  if(nagain.eq.1) then      !For nagain=1, use limits of +/- ntol
     nfa=max(100,1000-ntol)
     nfb=min(2500,1000+ntol)
  endif
  nsnr0=-99             !Default snr for no decode

! NB: Frequency of ipk is now shifted to 1000 Hz.
  call map65_mmdec(nutc,iwave,nqd,nsubmode,nfa,nfb,1000,ntol,     &
       newdat,nagain,max_drift,ndepth,mycall,hiscall,hisgrid)
   MHz=fcenter
  freq0=MHz + 0.001d0*ikhz

  if(nsnr0.gt.-99) then
     nq65df=nint(1000*(0.001*k0*df+nkhz_center-48.0+1.000-1.27046-ikhz))-nfcal
     nq65df=nq65df + nfreq0 - 1000
     ikhz1=ikhz
     ndf=nq65df
     if(ndf.gt.500) ikhz1=ikhz + (nq65df+500)/1000
     if(ndf.lt.-500) ikhz1=ikhz + (nq65df-500)/1000
     ndf=nq65df - 1000*(ikhz1-ikhz)
     freq1=freq0 + 0.001d0*(ikhz1-ikhz)
     ndecodes=ndecodes+1
     frx=0.001*k0*df+nkhz_center-48.0+1.0 - 0.001*nfcal
     fsked=frx - 0.001*ndop00/2.0 - 1.5
     write(result(ndecodes),1120) nutc,frx,fsked,xdt0,nsnr0,trim(msg0)
1120 format(i4.4,f9.3,f7.1,f7.2,i5,2x,a)
     write(12,1130) datetime,trim(result(ndecodes)(5:))
1130 format(a11,1x,a)
     result(ndecodes)=trim(result(ndecodes))//char(0)
     idec=0
  endif

900 flush(12)
  return
end subroutine q65b