subroutine q65_avg(nutc,ntrperiod,LL,ntol,lclearave,   &
     baud,nsubmode,ibwa,ibwb,codewords,ncw,xdt,f0,snr1,s3)

! Accumulate Q65 spectra s3(LL,63) and associated parameters for
! message averaging.

  use q65
  use packjt77
  character*37 avemsg
  character*1 cused(MAXAVE)
  character*6 cutc
  real s3(-64:LL-65,63)                  !Symbol spectra
  integer iused(MAXAVE)
  integer dat4(13)
  integer codewords(63,206)
  logical first,lclearave
  data first/.true./
  save

  if(first .or. LL.ne.LL0 .or.lclearave) then
     iutc=-1
     iseq=-1
     f0save=0.0
     dtdiff=0.2
     nsave=0
     LL0=LL
     first=.false.
     if(allocated(s3save)) deallocate(s3save)
     if(allocated(s3avg)) deallocate(s3avg)
     allocate(s3save(-64:LL-65,63,MAXAVE))
     allocate(s3avg(-64:LL-65,63))
     s3save=0.
     s3avg=0.
  endif

  if(ntrperiod.eq.15) then
     dtdiff=0.038
  else if(ntrperiod.eq.30) then
     dtdiff=0.08
  else if(ntrperiod.eq.60) then
     dtdiff=0.16
  else if(ntrperiod.eq.120) then
     dtdiff=0.4
  else if(ntrperiod.eq.300) then
     dtdiff=0.9
  endif

  do i=1,MAXAVE       !Don't save info more than once for same UTC and freq
     if(nutc.eq.iutc(i) .and. abs(nfreq-f0save(i)).le.ntol) go to 10
  enddo

! Save data for message averaging
  nsave=nsave+1
  n=nutc
  if(ntrperiod.ge.60) n=100*n
  write(cutc,'(i6.6)') n
  read(cutc,'(3i2)') ih,im,is
  nsec=3600*ih + 60*im + is
  iseq(nsave)=mod(nsec/ntrperiod,2)         !T/R sequence: 0 (even) or 1 (odd)
  iutc(nsave)=nutc                          !UTC, hhmm or hhmmss
  snr1save(nsave)=snr1                      !SNR from sync
  xdtsave(nsave)=xdt                        !DT
  f0save(nsave)=f0                           !f0
  s3save(:,:,nsave)=s3(:,:)                 !Symbol spectra

10 continue

!10 if(nsave.lt.2) go to 900
  snr1sum=0.
  xdtsum=0.
  fsum=0.
  navg=0
  s3avg=0.

! Find previously saved spectra that should be averaged with this one
  do i=1,MAXAVE
     cused(i)='.'                                   !Flag for "not used"
     if(iutc(i).lt.0) cycle
     if(iseq(i).ne.iseq(nsave)) cycle               !Sequence must match
!     write(*,3000) i,iseq(i),nutc,iutc(i),xdt-xdtsave(i),f0-f0save(i)
!3000 format(2i2,2i5,2f7.2)
     if(abs(xdt-xdtsave(i)).gt.dtdiff) cycle        !DT must be close
     if(abs(f0-f0save(i)).gt.float(ntol)) cycle   !Freq must match
!     write(*,3001) 'a',i,nsave,iseq(i),snr1,xdt,f0
!3001 format(a1,3i4,3f8.2)
     cused(i)='$'                                   !Flag for "use this one"
     s3avg=s3avg + s3save(:,:,i)                    !Add this spectrum
     snr1sum=snr1sum + snr1save(i)
     xdtsum=xdtsum + xdtsave(i)
     fsum=fsum + f0save(i)
     navg=navg+1
     iused(navg)=i
  enddo
  if(navg.lt.MAXAVE) iused(navg+1)=0

! Find averages of snr1, xdt, and f0 used in this decoding attempt.
  snr1ave=0.
  xdtave=0.
  fave=0.
  if(navg.gt.0) then
     snr1ave=snr1sum/navg
     xdtave=xdtsum/navg
     fave=fsum/navg
  endif

! Write parameters for display to User in the Message Averaging (F7) window.
  do i=1,nsave
     if(ntrperiod.le.30) write(14,1000) cused(i),iutc(i),snr1save(i),    &
          xdtsave(i),f0save(i)
1000 format(a1,i7.6,f6.1,f6.2,f7.1)
     if(ntrperiod.ge.60) write(14,1001) cused(i),iutc(i),snr1save(i),    &
          xdtsave(i),f0save(i)
1001 format(a1,i5.4,f6.1,f6.2,f7.1)
  enddo
!  if(navg.lt.2) go to 900                  !Must have at least 2

  s3avg=s3avg/navg
  nFadingModel=1
  do ibw=ibwa,ibwb
     b90=1.72**ibw
     b90ts=b90/baud
     call q65_dec1(s3,nsubmode,b90ts,codewords,ncw,esnodb,irc,dat4,avemsg)
     if(irc.ge.0 .and. plog.ge.PLOG_MIN) then
        snr2=esnodb - db(2500.0/baud) + 3.0     !Empirical adjustment
        id1=1                                   !###
!        print*,'B dec1 ',ibw,irc,avemsg
        exit
     endif
  enddo

  APmask=0
  APsymbols=0

  do ibw=ibwa,ibwb
     b90=1.72**ibw
     b90ts=b90/baud
     call q65_dec2(s3,nsubmode,b90ts,esnodb,irc,dat4,avemsg)
     if(irc.ge.0) then
        id2=iaptype+2
!        print*,'C dec2 ',ibw,irc,avemsg
        exit
     endif
  enddo  ! ibw (b90 loop)

  return
end subroutine q65_avg