diff --git a/CMakeLists.txt b/CMakeLists.txt
index e324f42d6..e3bb73c8d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -275,7 +275,6 @@ set (wsjt_FSRCS
   lib/astrosub.f90
   lib/astro0.f90
   lib/avecho.f90
-  lib/avg4.f90
   lib/azdist.f90
   lib/baddata.f90
   lib/ccf2.f90
@@ -350,7 +349,6 @@ set (wsjt_FSRCS
   lib/jplsubs.f
   lib/jt4.f90
   lib/jt4_decode.f90
-  lib/jt4a.f90
   lib/jt65_decode.f90
   lib/jt9_decode.f90
   lib/jt9fano.f90
@@ -942,7 +940,7 @@ add_executable (wsprsim ${wsprsim_CSRCS})
 add_executable (jt4code lib/jt4code.f90 wsjtx.rc)
 target_link_libraries (jt4code wsjt_fort wsjt_cxx)
 
-add_executable (jt65 lib/jt65.f90 ${jt65_CXXSRCS} wsjtx.rc)
+add_executable (jt65 lib/jt65.f90 lib/jt65_test.f90 wsjtx.rc)
 target_link_libraries (jt65 wsjt_fort wsjt_cxx ${FFTW3_LIBRARIES})
 
 add_executable (jt9 lib/jt9.f90 lib/jt9a.f90 ${jt9_CXXSRCS} wsjtx.rc)
diff --git a/commons.h b/commons.h
index 970221bdf..35f2200c9 100644
--- a/commons.h
+++ b/commons.h
@@ -6,7 +6,10 @@
 #define RX_SAMPLE_RATE 12000
 
 #ifdef __cplusplus
+#include <cstdbool>
 extern "C" {
+#else
+#include <stdbool.h>
 #endif
 
   /*
@@ -20,10 +23,10 @@ extern struct dec_data {
   struct
   {
     int nutc;                   //UTC as integer, HHMM
-    int ndiskdat;               //1 ==> data read from *.wav file
+    bool ndiskdat;              //true ==> data read from *.wav file
     int ntrperiod;              //TR period (seconds)
     int nfqso;                  //User-selected QSO freq (kHz)
-    int newdat;                 //1 ==> new data, must do long FFT
+    bool newdat;                //true ==> new data, must do long FFT
     int npts8;                  //npts for c0() array
     int nfa;                    //Low decode limit (Hz)
     int nfSplit;                //JT65 | JT9 split frequency
@@ -32,7 +35,7 @@ extern struct dec_data {
     int kin;
     int nzhsym;
     int nsubmode;
-    int nagain;
+    bool nagain;
     int ndepth;
     int ntxmode;
     int nmode;
@@ -46,7 +49,7 @@ extern struct dec_data {
     int n2pass;
     int nranera;
     int naggressive;
-    int nrobust;
+    bool nrobust;
     int nexp_decode;
     char datetime[20];
     char mycall[12];
diff --git a/lib/avg4.f90 b/lib/avg4.f90
index aac0d8081..fc37ec05c 100644
--- a/lib/avg4.f90
+++ b/lib/avg4.f90
@@ -1,140 +1,2 @@
-subroutine avg4(nutc,snrsync,dtxx,flip,nfreq,mode4,ntol,ndepth,neme,       &
-  mycall,hiscall,hisgrid,nfanoave,avemsg,qave,deepave,ichbest,ndeepave)
-
-! Decodes averaged JT4 data
-
-  use jt4
-  character*22 avemsg,deepave,deepbest
-  character mycall*12,hiscall*12,hisgrid*6
-  character*1 csync,cused(64)
-  real sym(207,7)
-  integer iused(64)
-  logical first
-  data first/.true./
-  save
-
-  if(first) then
-     iutc=-1
-     nfsave=0
-     dtdiff=0.2
-     first=.false.
-  endif
-
-  do i=1,64
-     if(nutc.eq.iutc(i) .and. abs(nhz-nfsave(i)).le.ntol) go to 10
-  enddo  
-
-! Save data for message averaging
-  iutc(nsave)=nutc
-  syncsave(nsave)=snrsync
-  dtsave(nsave)=dtxx
-  nfsave(nsave)=nfreq
-  flipsave(nsave)=flip
-  ppsave(1:207,1:7,nsave)=rsymbol(1:207,1:7)  
-
-10 sym=0.
-  syncsum=0.
-  dtsum=0.
-  nfsum=0
-  nsum=0
-
-  do i=1,64
-     cused(i)='.'
-     if(iutc(i).lt.0) cycle
-     if(mod(iutc(i),2).ne.mod(nutc,2)) cycle  !Use only same (odd/even) sequence
-     if(abs(dtxx-dtsave(i)).gt.dtdiff) cycle       !DT must match
-     if(abs(nfreq-nfsave(i)).gt.ntol) cycle        !Freq must match
-     if(flip.ne.flipsave(i)) cycle                 !Sync (*/#) must match
-     sym(1:207,1:7)=sym(1:207,1:7) +  ppsave(1:207,1:7,i)
-     syncsum=syncsum + syncsave(i)
-     dtsum=dtsum + dtsave(i)
-     nfsum=nfsum + nfsave(i)
-     cused(i)='$'
-     nsum=nsum+1
-     iused(nsum)=i
-  enddo
-  if(nsum.lt.64) iused(nsum+1)=0
-
-  syncave=0.
-  dtave=0.
-  fave=0.
-  if(nsum.gt.0) then
-     sym=sym/nsum
-     syncave=syncsum/nsum
-     dtave=dtsum/nsum
-     fave=float(nfsum)/nsum
-  endif
-
-!  rewind 80
-  do i=1,nsave
-     csync='*'
-     if(flipsave(i).lt.0.0) csync='#'
-     write(14,1000) cused(i),iutc(i),syncsave(i)-5.0,dtsave(i),nfsave(i),csync
-1000 format(a1,i5.4,f6.1,f6.2,i6,1x,a1)
-  enddo
-
-  sqt=0.
-  sqf=0.
-  do j=1,64
-     i=iused(j)
-     if(i.eq.0) exit
-     csync='*'
-     if(flipsave(i).lt.0.0) csync='#'
-!     write(80,3001) i,iutc(i),syncsave(i),dtsave(i),nfsave(i),csync
-!3001 format(i3,i6.4,f6.1,f6.2,i6,1x,a1)
-     sqt=sqt + (dtsave(i)-dtave)**2
-     sqf=sqf + (nfsave(i)-fave)**2
-  enddo
-  rmst=0.
-  rmsf=0.
-  if(nsum.ge.2) then
-     rmst=sqrt(sqt/(nsum-1))
-     rmsf=sqrt(sqf/(nsum-1))
-  endif
-!  write(80,3002)
-!3002 format(16x,'----- -----')
-!  write(80,3003) dtave,nint(fave)
-!  write(80,3003) rmst,nint(rmsf)
-!3003 format(15x,f6.2,i6)
-!  flush(80)
-
-!  nadd=nused*mode4
-  kbest=ich1
-  do k=ich1,ich2
-     call extract4(sym(1,k),ncount,avemsg)     !Do the Fano decode
-     nfanoave=0
-     if(ncount.ge.0) then
-        ichbest=k
-        nfanoave=nsum
-        go to 900
-     endif
-     if(nch(k).ge.mode4) exit
-  enddo
-
-  deepave='                      '
-  qave=0.
-
-! Possibly should pass nadd=nused, also ?
-  if(ndepth.ge.3) then
-     flipx=1.0                     !Normal flip not relevant for ave msg
-     qbest=0.
-     do k=ich1,ich2
-        call deep4(sym(2,k),neme,flipx,mycall,hiscall,hisgrid,deepave,qave)
-!        write(82,3101) nutc,sym(51:53,k),flipx,k,qave,deepave
-!3101    format(i4.4,4f8.1,i3,f7.2,2x,a22)
-        if(qave.gt.qbest) then
-           qbest=qave
-           deepbest=deepave
-           kbest=k
-           ndeepave=nsum
-        endif
-        if(nch(k).ge.mode4) exit
-     enddo
-
-     deepave=deepbest
-     qave=qbest
-     ichbest=kbest
-  endif
-
-900 return
-end subroutine avg4
+  ! The contents of this file have been migrated to lib/jt4_decode.f90
+  
diff --git a/lib/decoder.f90 b/lib/decoder.f90
index b611cc61b..c0a206129 100644
--- a/lib/decoder.f90
+++ b/lib/decoder.f90
@@ -1,46 +1,64 @@
-subroutine decoder(ss,id2,params,nfsample)
+subroutine multimode_decoder(ss,id2,params,nfsample)
 
   !$ use omp_lib
   use prog_args
   use timer_module, only: timer
+  use jt4_decode
+  use jt65_decode
+  use jt9_decode
 
   include 'jt9com.f90'
   include 'timer_common.inc'
 
+  type, extends(jt4_decoder) :: counting_jt4_decoder
+     integer :: decoded
+  end type counting_jt4_decoder
+
+  type, extends(jt65_decoder) :: counting_jt65_decoder
+     integer :: decoded
+  end type counting_jt65_decoder
+
+  type, extends(jt9_decoder) :: counting_jt9_decoder
+     integer :: decoded
+  end type counting_jt9_decoder
+
   real ss(184,NSMAX)
-  logical baddata
+  logical baddata,newdat65,newdat9
   integer*2 id2(NTMAX*12000)
   type(params_block) :: params
   real*4 dd(NTMAX*12000)
   save
+  type(counting_jt4_decoder) :: my_jt4
+  type(counting_jt65_decoder) :: my_jt65
+  type(counting_jt9_decoder) :: my_jt9
 
   if(mod(params%nranera,2).eq.0) ntrials=10**(params%nranera/2)
   if(mod(params%nranera,2).eq.1) ntrials=3*10**(params%nranera/2)
   if(params%nranera.eq.0) ntrials=0
 
-  rms=sqrt(dot_product(float(id2(300000:310000)),                            &
-                       float(id2(300000:310000)))/10000.0)
+  rms=sqrt(dot_product(float(id2(300000:310000)),                                           &
+       float(id2(300000:310000)))/10000.0)
   if(rms.lt.2.0) go to 800 
 
-  if (params%nagain .eq. 0) then
-     open(13,file=trim(temp_dir)//'/decoded.txt',status='unknown')
-  else
-     open(13,file=trim(temp_dir)//'/decoded.txt',status='unknown',      &
+  if (params%nagain) then
+     open(13,file=trim(temp_dir)//'/decoded.txt',status='unknown',                          &
           position='append')
+  else
+     open(13,file=trim(temp_dir)//'/decoded.txt',status='unknown')
   end if
   if(params%nmode.eq.4 .or. params%nmode.eq.65) open(14,file=trim(temp_dir)//'/avemsg.txt', &
        status='unknown')
 
   if(params%nmode.eq.4) then
      jz=52*nfsample
-     if(params%newdat.ne.0) then
+     if(params%newdat) then
         if(nfsample.eq.12000) call wav11(id2,jz,dd)
         if(nfsample.eq.11025) dd(1:jz)=id2(1:jz)
      endif
-     call jt4a(dd,jz,params%nutc,params%nfqso,params%ntol,params%emedelay,params%dttol,  &
-          params%nagain,params%ndepth,params%nclearave,params%minsync,params%minw,       &
-          params%nsubmode,params%mycall,params%hiscall,params%hisgrid,                   &
-          params%nlist,params%listutc)
+     call my_jt4%decode(jt4_decoded,dd,jz,params%nutc,params%nfqso,params%ntol,             &
+          params%emedelay,params%dttol,logical(params%nagain),params%ndepth,                &
+          params%nclearave,params%minsync,params%minw,params%nsubmode,params%mycall,        &
+          params%hiscall,params%hisgrid,params%nlist,params%listutc,jt4_average)
      go to 800
   endif
 
@@ -55,52 +73,56 @@ subroutine decoder(ss,id2,params,nfsample)
   newdat65=params%newdat
   newdat9=params%newdat
 
-!$ call omp_set_dynamic(.true.)
-!$omp parallel sections num_threads(2) copyin(/timer_private/) shared(ndecoded) if(.true.) !iif() needed on Mac
+  !$call omp_set_dynamic(.true.)
+  !$omp parallel sections num_threads(2) copyin(/timer_private/) shared(ndecoded) if(.true.) !iif() needed on Mac
 
-!$omp section
+  !$omp section
   if(params%nmode.eq.65 .or. (params%nmode.eq.(65+9) .and. params%ntxmode.eq.65)) then
-! We're in JT65 mode, or should do JT65 first
-     if(newdat65.ne.0) dd(1:npts65)=id2(1:npts65)
+     ! We're in JT65 mode, or should do JT65 first
+     if(newdat65) dd(1:npts65)=id2(1:npts65)
      nf1=params%nfa
      nf2=params%nfb
      call timer('jt65a   ',0)
-     call jt65a(dd,npts65,newdat65,params%nutc,nf1,nf2,params%nfqso,ntol65,params%nsubmode,      &
-          params%minsync,params%nagain,params%n2pass,params%nrobust,ntrials,params%naggressive,  &
-          params%ndepth,params%mycall,params%hiscall,params%hisgrid,params%nexp_decode,ndecoded)
+     call my_jt65%decode(jt65_decoded,dd,npts65,newdat65,params%nutc,nf1,nf2,params%nfqso,  &
+          ntol65,params%nsubmode,params%minsync,logical(params%nagain),params%n2pass,       &
+          logical(params%nrobust),ntrials,params%naggressive,params%ndepth,params%mycall,   &
+          params%hiscall,params%hisgrid,params%nexp_decode)
      call timer('jt65a   ',1)
 
   else if(params%nmode.eq.9 .or. (params%nmode.eq.(65+9) .and. params%ntxmode.eq.9)) then
-! We're in JT9 mode, or should do JT9 first
+     ! We're in JT9 mode, or should do JT9 first
      call timer('decjt9  ',0)
-     call decjt9(ss,id2,params%nutc,params%nfqso,newdat9,params%npts8,params%nfa,params%nfsplit,  &
-          params%nfb,params%ntol,params%nzhsym,params%nagain,params%ndepth,params%nmode)
+     call my_jt9%decode(jt9_decoded,ss,id2,params%nutc,params%nfqso,newdat9,params%npts8,   &
+          params%nfa,params%nfsplit,params%nfb,params%ntol,params%nzhsym,                   &
+          logical(params%nagain),params%ndepth,params%nmode)
      call timer('decjt9  ',1)
   endif
 
-!$omp section
+  !$omp section
   if(params%nmode.eq.(65+9)) then          !Do the other mode (we're in dual mode)
      if (params%ntxmode.eq.9) then
-        if(newdat65.ne.0) dd(1:npts65)=id2(1:npts65)
+        if(newdat65) dd(1:npts65)=id2(1:npts65)
         nf1=params%nfa
         nf2=params%nfb
         call timer('jt65a   ',0)
-        call jt65a(dd,npts65,newdat65,params%nutc,nf1,nf2,params%nfqso,ntol65,params%nsubmode,   &
-             params%minsync,params%nagain,params%n2pass,params%nrobust,ntrials,                  &
-             params%naggressive,params%ndepth,params%mycall,params%hiscall,params%hisgrid,       &
-             params%nexp_decode,ndecoded)
+        call my_jt65%decode(jt65_decoded,dd,npts65,newdat65,params%nutc,nf1,nf2,            &
+             params%nfqso,ntol65,params%nsubmode,params%minsync,logical(params%nagain),     &
+             params%n2pass,logical(params%nrobust),ntrials,params%naggressive,params%ndepth,&
+             params%mycall,params%hiscall,params%hisgrid,params%nexp_decode)
         call timer('jt65a   ',1)
      else
         call timer('decjt9  ',0)
-        call decjt9(ss,id2,params%nutc,params%nfqso,newdat9,params%npts8,params%nfa,params%nfsplit,  &
-             params%nfb,params%ntol,params%nzhsym,params%nagain,params%ndepth,params%nmode)
+        call my_jt9%decode(jt9_decoded,ss,id2,params%nutc,params%nfqso,newdat9,params%npts8,&
+             params%nfa,params%nfsplit,params%nfb,params%ntol,params%nzhsym,                &
+             logical(params%nagain),params%ndepth,params%nmode)
         call timer('decjt9  ',1)
      end if
   endif
 
-!$omp end parallel sections
+  !$omp end parallel sections
 
-! JT65 is not yet producing info for nsynced, ndecoded.
+  ! JT65 is not yet producing info for nsynced, ndecoded.
+  ndecoded = my_jt4%decoded + my_jt65%decoded + my_jt9%decoded
 800 write(*,1010) nsynced,ndecoded
 1010 format('<DecodeFinished>',2i4)
   call flush(6)
@@ -108,4 +130,130 @@ subroutine decoder(ss,id2,params,nfsample)
   if(params%nmode.eq.4 .or. params%nmode.eq.65) close(14)
 
   return
-end subroutine decoder
+
+contains
+
+  subroutine jt4_decoded (this, utc, snr, dt, freq, have_sync, sync, is_deep, decoded, qual,&
+       ich, is_average, ave)
+    implicit none
+    class(jt4_decoder), intent(inout) :: this
+    integer, intent(in) :: utc
+    integer, intent(in) :: snr
+    real, intent(in) :: dt
+    integer, intent(in) :: freq
+    logical, intent(in) :: have_sync
+    logical, intent(in) :: is_deep
+    character(len=1), intent(in) :: sync
+    character(len=22), intent(in) :: decoded
+    real, intent(in) :: qual
+    integer, intent(in) :: ich
+    logical, intent(in) :: is_average
+    integer, intent(in) :: ave
+
+    character*2 :: cqual
+
+    if (have_sync) then
+       if (int(qual).gt.0) then
+          write(cqual, '(i2)') int(qual)
+          if (ave.gt.0) then
+             write(*,1000) utc ,snr, dt, freq, sync, decoded, cqual,                        &
+                  char(ichar('A')+ich-1), ave
+          else
+             write(*,1000) utc ,snr, dt, freq, sync, decoded, cqual, char(ichar('A')+ich-1)
+          end if
+       else
+          write(*,1000) utc ,snr, dt, freq, sync, decoded, ' *', char(ichar('A')+ich-1)
+       end if
+    else
+       write(*,1000) utc ,snr, dt, freq
+    end if
+1000 format(i4.4,i4,f5.2,i5,1x,a1,1x,a22,a2,1x,a1,i3)
+    select type(this)
+    type is (counting_jt4_decoder)
+       this%decoded = this%decoded + 1
+    end select
+  end subroutine jt4_decoded
+
+  subroutine jt4_average (this, used, utc, sync, dt, freq, flip)
+    implicit none
+    class(jt4_decoder), intent(inout) :: this
+    logical, intent(in) :: used
+    integer, intent(in) :: utc
+    real, intent(in) :: sync
+    real, intent(in) :: dt
+    integer, intent(in) :: freq
+    logical, intent(in) :: flip
+
+    character(len=1) :: cused='.', csync='*'
+
+    if (used) cused = '$'
+    if (flip) csync = '$'
+    write(14,1000) cused,utc,sync,dt,freq,csync
+1000 format(a1,i5.4,f6.1,f6.2,i6,1x,a1)
+  end subroutine jt4_average
+
+  subroutine jt65_decoded (this, utc, sync, snr, dt, freq, drift, decoded, ft, qual,        &
+       candidates, tries, total_min, hard_min, aggression)
+    use jt65_decode
+    implicit none
+
+    class(jt65_decoder), intent(inout) :: this
+    integer, intent(in) :: utc
+    real, intent(in) :: sync
+    integer, intent(in) :: snr
+    real, intent(in) :: dt
+    integer, intent(in) :: freq
+    integer, intent(in) :: drift
+    character(len=22), intent(in) :: decoded
+    integer, intent(in) :: ft
+    integer, intent(in) :: qual
+    integer, intent(in) :: candidates
+    integer, intent(in) :: tries
+    integer, intent(in) :: total_min
+    integer, intent(in) :: hard_min
+    integer, intent(in) :: aggression
+
+    !$omp critical(decode_results)
+    write(*,1010) utc,snr,dt,freq,decoded
+1010 format(i4.4,i4,f5.1,i5,1x,'#',1x,a22)
+    write(13,1012) utc,nint(sync),snr,dt,float(freq),drift,decoded,ft
+1012 format(i4.4,i4,i5,f6.1,f8.0,i4,3x,a22,' JT65',i4)
+    call flush(6)
+    !          write(79,3001) utc,nint(sync),snr,dt,freq,candidates,    &
+    write(79,3001) utc,sync,snr,dt,freq,candidates,    &
+         hard_min,total_min,tries,aggression,ft,qual,decoded
+3001 format(i4.4,f6.2,i4,f6.2,i5,i7,i3,i4,i8,i3,i2,i5,1x,a22)
+    !$omp end critical(decode_results)
+    select type(this)
+    type is (counting_jt65_decoder)
+       this%decoded = this%decoded + 1
+    end select
+  end subroutine jt65_decoded
+
+  subroutine jt9_decoded (this, utc, sync, snr, dt, freq, drift, decoded)
+    use jt9_decode
+    implicit none
+
+    class(jt9_decoder), intent(inout) :: this
+    integer, intent(in) :: utc
+    real, intent(in) :: sync
+    integer, intent(in) :: snr
+    real, intent(in) :: dt
+    real, intent(in) :: freq
+    integer, intent(in) :: drift
+    character(len=22), intent(in) :: decoded
+
+    !$omp critical(decode_results)
+    write(*,1000) utc,snr,dt,nint(freq),decoded
+1000 format(i4.4,i4,f5.1,i5,1x,'@',1x,a22)
+    write(13,1002) utc,nint(sync),snr,dt,freq,drift,decoded
+1002 format(i4.4,i4,i5,f6.1,f8.0,i4,3x,a22,' JT9')
+    call flush(6)
+    !$omp end critical(decode_results)
+    select type(this)
+    type is (counting_jt9_decoder)
+       this%decoded = this%decoded + 1
+    end select
+  end subroutine jt9_decoded
+
+end subroutine multimode_decoder
diff --git a/lib/downsam9.f90 b/lib/downsam9.f90
index 3eba1d091..7cd1962a1 100644
--- a/lib/downsam9.f90
+++ b/lib/downsam9.f90
@@ -13,6 +13,7 @@ subroutine downsam9(id2,npts8,nsps8,newdat,nspsd,fpk,c2)
   parameter (NFFT1=653184,NFFT2=1512)
   type(C_PTR) :: plan                        !Pointers plan for big FFT
   integer*2 id2(0:8*npts8-1)
+  logical, intent(inout) :: newdat
   real*4, pointer :: x1(:)
   complex c1(0:NFFT1/2)
   complex c2(0:NFFT2-1)
@@ -46,7 +47,7 @@ subroutine downsam9(id2,npts8,nsps8,newdat,nspsd,fpk,c2)
      first=.false.
   endif
 
-  if(newdat.eq.1) then
+  if(newdat) then
      x1(0:npts-1)=id2(0:npts-1)
      x1(npts:NFFT1-1)=0.                      !Zero the rest of x1
      call timer('FFTbig9 ',0)
@@ -62,7 +63,7 @@ subroutine downsam9(id2,npts8,nsps8,newdat,nspsd,fpk,c2)
            s(i)=s(i)+real(c1(j))**2 + aimag(c1(j))**2
         enddo
      enddo
-     newdat=0
+     newdat=.false.
   endif
 
   ndown=8*nsps8/nspsd                      !Downsample factor = 432
diff --git a/lib/jt4_decode.f90 b/lib/jt4_decode.f90
index 67571ea12..dd155323f 100644
--- a/lib/jt4_decode.f90
+++ b/lib/jt4_decode.f90
@@ -1,182 +1,451 @@
-subroutine wsjt4(dat,npts,nutc,NClearAve,minsync,ntol,emedelay,dttol,    &
-     mode4,minw,mycall,hiscall,hisgrid,nfqso,NAgain,ndepth,neme)
+module jt4_decode
+  type :: jt4_decoder
+     procedure(jt4_decode_callback), pointer :: decode_callback => null ()
+     procedure(jt4_average_callback), pointer :: average_callback => null ()
+   contains
+     procedure :: decode
+     procedure, private :: wsjt4, avg4
+  end type jt4_decoder
 
-! Orchestrates the process of decoding JT4 messages, using data that 
-! have been 2x downsampled.
+  !
+  ! Callback function to be called with each decode
+  !
+  abstract interface
+     subroutine jt4_decode_callback (this, utc, snr, dt, freq, have_sync,     &
+          sync, is_deep, decoded, qual, ich, is_average, ave)
+       import jt4_decoder
+       implicit none
+       class(jt4_decoder), intent(inout) :: this
+       integer, intent(in) :: utc
+       integer, intent(in) :: snr
+       real, intent(in) :: dt
+       integer, intent(in) :: freq
+       logical, intent(in) :: have_sync
+       logical, intent(in) :: is_deep
+       character(len=1), intent(in) :: sync
+       character(len=22), intent(in) :: decoded
+       real, intent(in) :: qual
+       integer, intent(in) :: ich
+       logical, intent(in) :: is_average
+       integer, intent(in) :: ave
+     end subroutine jt4_decode_callback
+  end interface
 
-! NB: JT4 presently looks for only one decodable signal in the FTol 
-! range -- analogous to the nqd=1 step in JT9 and JT65.
+  !
+  ! Callback function to be called with each average result
+  !
+  abstract interface
+     subroutine jt4_average_callback (this, used, utc, sync, dt, freq, flip)
+       import jt4_decoder
+       implicit none
+       class(jt4_decoder), intent(inout) :: this
+       logical, intent(in) :: used
+       integer, intent(in) :: utc
+       real, intent(in) :: sync
+       real, intent(in) :: dt
+       integer, intent(in) :: freq
+       logical, intent(in) :: flip
+     end subroutine jt4_average_callback
+  end interface
 
-  use jt4
-  use timer_module, only: timer
+contains
 
-  real dat(npts)                                     !Raw data
-  real z(458,65)
-  logical first,prtavg
-  character decoded*22,special*5
-  character*22 avemsg,deepmsg,deepave,blank,deepmsg0,deepave1
-  character csync*1,cqual*2
-  character*12 mycall
-  character*12 hiscall
-  character*6 hisgrid
-  data first/.true./,nutc0/-999/,nfreq0/-999999/
-  save
+  subroutine decode(this,decode_callback,dd,jz,nutc,nfqso,ntol0,emedelay,     &
+       dttol,nagain,ndepth,nclearave,minsync,minw,nsubmode,mycall,hiscall,    &
+       hisgrid,nlist0,listutc0,average_callback)
 
-  if(first) then
-     nsave=0
-     first=.false.
-     blank='                      '
-     ccfblue=0.
-     ccfred=0.
-     nagain=0
-  endif
+    use jt4
+    use timer_module, only: timer
 
-  zz=0.
-  syncmin=3.0 + minsync
-  naggressive=0
-  if(ndepth.ge.2) naggressive=1
-  nq1=3
-  nq2=6
-  if(naggressive.eq.1) nq1=1
-  if(NClearAve.ne.0) then
-     nsave=0
-     iutc=-1
-     nfsave=0.
-     listutc=0
-     ppsave=0.
-     rsymbol=0.
-     dtsave=0.
-     syncsave=0.
-     nfanoave=0
-     ndeepave=0
-  endif
+    class(jt4_decoder), intent(inout) :: this
+    procedure(jt4_decode_callback) :: decode_callback
+    integer, intent(in) :: jz,nutc,nfqso,ntol0,ndepth,nclearave,              &
+         minsync,minw,nsubmode,nlist0,listutc0(10)
+    real, intent(in) :: dd(jz),emedelay,dttol
+    logical, intent(in) :: nagain
+    character(len=12), intent(in) :: mycall,hiscall
+    character(len=6), intent(in) :: hisgrid
+    procedure(jt4_average_callback), optional :: average_callback
 
-! Attempt to synchronize: look for sync pattern, get DF and DT.
-  call timer('sync4   ',0)
-  call sync4(dat,npts,mode4,minw)
-  call timer('sync4   ',1)
+    real*4 dat(30*12000)
+    character*6 cfile6
 
-  call timer('zplt    ',0)
-  do ich=4,7
-     z(1:458,1:65)=zz(274:731,1:65,ich)
-     call zplt(z,ich-4,syncz,dtxz,nfreqz,flipz,sync2z,0,emedelay,dttol,   &
-          nfqso,ntol)
-     if(ich.eq.5) then
-        dtxzz=dtxz
-        nfreqzz=nfreqz
-     endif
-  enddo
-  call timer('zplt    ',1)
+    this%decode_callback => decode_callback
+    if (present (average_callback)) then
+       this%average_callback => average_callback
+    end if
+    mode4=nch(nsubmode+1)
+    ntol=ntol0
+    neme=0
+    lumsg=6                         !### temp ? ###
+    ndiag=1
+    nlist=nlist0
+    listutc=listutc0
 
-! Use results from zplt
-  flip=flipz
-  sync=syncz
-  snrx=db(sync) - 26.
-  nsnr=nint(snrx)
-  if(sync.lt.syncmin) then
-     write(*,1010) nutc,nsnr,dtxz,nfreqz
-     go to 990
-  endif
+    ! Lowpass filter and decimate by 2
+    call timer('lpf1    ',0)
+    call lpf1(dd,jz,dat,jz2)
+    call timer('lpf1    ',1)
 
-! We have achieved sync
-  decoded=blank
-  deepmsg=blank
-  special='     '
-  nsync=sync
-  nsnrlim=-33
-  csync='*'
-  if(flip.lt.0.0) csync='#'
-  qbest=0.
-  qabest=0.
-  prtavg=.false.
+    !i=index(MyCall,char(0))
+    !if(i.le.0) i=index(MyCall,' ')
+    !mycall=MyCall(1:i-1)//'            '
+    !i=index(HisCall,char(0))
+    !if(i.le.0) i=index(HisCall,' ')
+    !hiscall=HisCall(1:i-1)//'            '
 
-  do idt=-2,2
-     dtx=dtxz + 0.03*idt
-     nfreq=nfreqz + 2*idf
+    write(cfile6(1:4),1000) nutc
+1000 format(i4.4)
+    cfile6(5:6)='  '
+
+    call timer('wsjt4   ',0)
+    call this%wsjt4(dat,jz2,nutc,NClearAve,minsync,ntol,emedelay,dttol,mode4, &
+         minw,mycall,hiscall,hisgrid,nfqso,NAgain,ndepth,neme)
+    call timer('wsjt4   ',1)
+
+    return
+  end subroutine decode
+
+  subroutine wsjt4(this,dat,npts,nutc,NClearAve,minsync,ntol,emedelay,dttol,  &
+       mode4,minw,mycall,hiscall,hisgrid,nfqso,NAgain,ndepth,neme)
+
+    ! Orchestrates the process of decoding JT4 messages, using data that 
+    ! have been 2x downsampled.
+
+    ! NB: JT4 presently looks for only one decodable signal in the FTol 
+    ! range -- analogous to the nqd=1 step in JT9 and JT65.
+
+    use jt4
+    use timer_module, only: timer
+
+    class(jt4_decoder), intent(inout) :: this
+    integer, intent(in) :: npts,nutc,NClearAve,minsync,ntol,mode4,minw,       &
+         nfqso,ndepth,neme
+    logical, intent(in) :: NAgain
+    character(len=12), intent(in) :: mycall,hiscall
+    character(len=6), intent(in) :: hisgrid
+
+    real, intent(in) :: dat(npts) !Raw data
+    real z(458,65)
+    logical first,prtavg
+    character decoded*22,special*5
+    character*22 avemsg,deepmsg,deepave,blank,deepmsg0,deepave1
+    character csync*1
+    data first/.true./,nutc0/-999/,nfreq0/-999999/
+    save
+
+    if(first) then
+       nsave=0
+       first=.false.
+       blank='                      '
+       ccfblue=0.
+       ccfred=0.
+       !nagain=.false.
+    endif
+
+    zz=0.
+    syncmin=3.0 + minsync
+    naggressive=0
+    if(ndepth.ge.2) naggressive=1
+    nq1=3
+    nq2=6
+    if(naggressive.eq.1) nq1=1
+    if(NClearAve.ne.0) then
+       nsave=0
+       iutc=-1
+       nfsave=0.
+       listutc=0
+       ppsave=0.
+       rsymbol=0.
+       dtsave=0.
+       syncsave=0.
+       nfanoave=0
+       ndeepave=0
+    endif
+
+    ! Attempt to synchronize: look for sync pattern, get DF and DT.
+    call timer('sync4   ',0)
+    call sync4(dat,npts,mode4,minw)
+    call timer('sync4   ',1)
+
+    call timer('zplt    ',0)
+    do ich=4,7
+       z(1:458,1:65)=zz(274:731,1:65,ich)
+       call zplt(z,ich-4,syncz,dtxz,nfreqz,flipz,sync2z,0,emedelay,dttol,     &
+            nfqso,ntol)
+       if(ich.eq.5) then
+          dtxzz=dtxz
+          nfreqzz=nfreqz
+       endif
+    enddo
+    call timer('zplt    ',1)
+
+    ! Use results from zplt
+    flip=flipz
+    sync=syncz
+    snrx=db(sync) - 26.
+    nsnr=nint(snrx)
+    if(sync.lt.syncmin) then
+       if (associated (this%decode_callback)) then
+          call this%decode_callback(nutc,nsnr,dtxz,nfreqz,.false.,csync,      &
+               .false.,decoded,0.,ich,.false.,0)
+       end if
+       go to 990
+    endif
+
+    ! We have achieved sync
+    decoded=blank
+    deepmsg=blank
+    special='     '
+    nsync=sync
+    nsnrlim=-33
+    csync='*'
+    if(flip.lt.0.0) csync='#'
+    qbest=0.
+    qabest=0.
+    prtavg=.false.
+
+    do idt=-2,2
+       dtx=dtxz + 0.03*idt
+       nfreq=nfreqz + 2*idf
 
 
-! Attempt a single-sequence decode, including deep4 if Fano fails.
-     call timer('decode4 ',0)
-     call decode4(dat,npts,dtx,nfreq,flip,mode4,ndepth,neme,minw,             &
-          mycall,hiscall,hisgrid,decoded,nfano,deepmsg,qual,ich)
-     call timer('decode4 ',1)
+       ! Attempt a single-sequence decode, including deep4 if Fano fails.
+       call timer('decode4 ',0)
+       call decode4(dat,npts,dtx,nfreq,flip,mode4,ndepth,neme,minw,           &
+            mycall,hiscall,hisgrid,decoded,nfano,deepmsg,qual,ich)
+       call timer('decode4 ',1)
 
-     if(nfano.gt.0) then
-! Fano succeeded: display the message and return                      FANO OK
-        write(*,1010) nutc,nsnr,dtx,nfreq,csync,decoded,' *',                 &
-             char(ichar('A')+ich-1)
-1010    format(i4.4,i4,f5.2,i5,1x,a1,1x,a22,a2,1x,a1,i3)
-        nsave=0
-        go to 990
+       if(nfano.gt.0) then
+          ! Fano succeeded: report the message and return               FANO OK
+          if (associated (this%decode_callback)) then
+             call this%decode_callback(nutc,nsnr,dtx,nfreq,.true.,csync,      &
+                  .false.,decoded,0.,ich,.false.,0)
+          end if
+          nsave=0
+          go to 990
 
-     else          !                                                 NO FANO 
-        if(qual.gt.qbest) then
-           dtx0=dtx
-           nfreq0=nfreq
-           deepmsg0=deepmsg
-           ich0=ich
-           qbest=qual
-        endif
-     endif
+       else          !                                                  NO FANO 
+          if(qual.gt.qbest) then
+             dtx0=dtx
+             nfreq0=nfreq
+             deepmsg0=deepmsg
+             ich0=ich
+             qbest=qual
+          endif
+       endif
 
-     if(idt.ne.0) cycle
-! Single-sequence Fano decode failed, so try for an average Fano decode:
-     qave=0.
-! If this is a new minute or a new frequency, call avg4
-     if(.not. prtavg) then
-        if(nutc.ne.nutc0 .or. abs(nfreq-nfreq0).gt.ntol) then
-           nutc0=nutc                                   !            TRY AVG
-           nfreq0=nfreq
-           nsave=nsave+1
-           nsave=mod(nsave-1,64)+1
-           call timer('avg4    ',0)
-           call avg4(nutc,sync,dtx,flip,nfreq,mode4,ntol,ndepth,neme,       &
-                mycall,hiscall,hisgrid,nfanoave,avemsg,qave,deepave,ich,    &
-                ndeepave)
-           call timer('avg4    ',1)
-        endif
+       if(idt.ne.0) cycle
+       ! Single-sequence Fano decode failed, so try for an average Fano decode:
+       qave=0.
+       ! If this is a new minute or a new frequency, call avg4
+       if(.not. prtavg) then
+          if(nutc.ne.nutc0 .or. abs(nfreq-nfreq0).gt.ntol) then
+             nutc0=nutc                                   !             TRY AVG
+             nfreq0=nfreq
+             nsave=nsave+1
+             nsave=mod(nsave-1,64)+1
+             call timer('avg4    ',0)
+             call this%avg4(nutc,sync,dtx,flip,nfreq,mode4,ntol,ndepth,neme,  &
+                  mycall,hiscall,hisgrid,nfanoave,avemsg,qave,deepave,ich,    &
+                  ndeepave)
+             call timer('avg4    ',1)
+          endif
 
-        if(nfanoave.gt.0) then
-! Fano succeeded: display the message                           AVG FANO OK
-           write(*,1010) nutc,nsnr,dtx,nfreq,csync,avemsg,' *',             &
-                char(ichar('A')+ich-1),nfanoave
-           prtavg=.true.
-           cycle
-        else
-           if(qave.gt.qabest) then
-              dtx1=dtx
-              nfreq1=nfreq
-              deepave1=deepave
-              ich1=ich
-              qabest=qave
-           endif
-        endif
-     endif
-  enddo
+          if(nfanoave.gt.0) then
+             ! Fano succeeded: report the mess                      AVG FANO OK
+             if (associated (this%decode_callback)) then
+                call this%decode_callback(nutc,nsnr,dtx,nfreq,.true.,csync,   &
+                     .false.,avemsg,0.,ich,.true.,nfanoave)
+             end if
+             prtavg=.true.
+             cycle
+          else
+             if(qave.gt.qabest) then
+                dtx1=dtx
+                nfreq1=nfreq
+                deepave1=deepave
+                ich1=ich
+                qabest=qave
+             endif
+          endif
+       endif
+    enddo
 
-  dtx=dtx0
-  nfreq=nfreq0
-  deepmsg=deepmsg0
-  ich=ich0
-  qual=qbest
-  if(int(qual).ge.nq1) then
-     write(cqual,'(i2)') int(qual)
-     write(*,1010) nutc,nsnr,dtx,nfreq,csync,         &
-          deepmsg,cqual,char(ichar('A')+ich-1)
-  else
-     write(*,1010) nutc,nsnr,dtxz,nfreqz,csync
-  endif
+    dtx=dtx0
+    nfreq=nfreq0
+    deepmsg=deepmsg0
+    ich=ich0
+    qual=qbest
+    if (associated (this%decode_callback)) then
+       if(int(qual).ge.nq1) then
+          call this%decode_callback(nutc,nsnr,dtx,nfreqz,.true.,csync,.true., &
+               deepmsg,qual,ich,.false.,0)
+       else
+          call this%decode_callback(nutc,nsnr,dtxz,nfreqz,.true.,csync,       &
+               .false.,blank,0.,ich,.false.,0)
+       endif
+    end if
 
-  dtx=dtx1
-  nfreq=nfreq1
-  deepave=deepave1
-  ich=ich1
-  qave=qabest
-  if(int(qave).ge.nq1) then
-     write(cqual,'(i2)') nint(qave)
-     write(*,1010) nutc,nsnr,dtx,nfreq,csync,     &
-          deepave,cqual,char(ichar('A')+ich-1),ndeepave
-  endif
+    dtx=dtx1
+    nfreq=nfreq1
+    deepave=deepave1
+    ich=ich1
+    qave=qabest
+    if (associated (this%decode_callback)) then
+       if(int(qave).ge.nq1) then
+          call this%decode_callback(nutc,nsnr,dtx,nfreq,.true.,csync,.true.,  &
+               deepave,qave,ich,.true.,ndeepave)
+       endif
+    end if
 
 990 return
-end subroutine wsjt4
+  end subroutine wsjt4
+
+  subroutine avg4(this,nutc,snrsync,dtxx,flip,nfreq,mode4,ntol,ndepth,neme,   &
+       mycall,hiscall,hisgrid,nfanoave,avemsg,qave,deepave,ichbest,ndeepave)
+
+    ! Decodes averaged JT4 data
+
+    use jt4
+    class(jt4_decoder), intent(inout) :: this
+
+    character*22 avemsg,deepave,deepbest
+    character mycall*12,hiscall*12,hisgrid*6
+    character*1 csync,cused(64)
+    real sym(207,7)
+    integer iused(64)
+    logical first
+    data first/.true./
+    save
+
+    if(first) then
+       iutc=-1
+       nfsave=0
+       dtdiff=0.2
+       first=.false.
+    endif
+
+    do i=1,64
+       if(nutc.eq.iutc(i) .and. abs(nhz-nfsave(i)).le.ntol) go to 10
+    enddo
+
+    ! Save data for message averaging
+    iutc(nsave)=nutc
+    syncsave(nsave)=snrsync
+    dtsave(nsave)=dtxx
+    nfsave(nsave)=nfreq
+    flipsave(nsave)=flip
+    ppsave(1:207,1:7,nsave)=rsymbol(1:207,1:7)  
+
+10  sym=0.
+    syncsum=0.
+    dtsum=0.
+    nfsum=0
+    nsum=0
+
+    do i=1,64
+       cused(i)='.'
+       if(iutc(i).lt.0) cycle
+       if(mod(iutc(i),2).ne.mod(nutc,2)) cycle  !Use only same (odd/even) sequence
+       if(abs(dtxx-dtsave(i)).gt.dtdiff) cycle  !DT must match
+       if(abs(nfreq-nfsave(i)).gt.ntol) cycle   !Freq must match
+       if(flip.ne.flipsave(i)) cycle            !Sync (*/#) must match
+       sym(1:207,1:7)=sym(1:207,1:7) +  ppsave(1:207,1:7,i)
+       syncsum=syncsum + syncsave(i)
+       dtsum=dtsum + dtsave(i)
+       nfsum=nfsum + nfsave(i)
+       cused(i)='$'
+       nsum=nsum+1
+       iused(nsum)=i
+    enddo
+    if(nsum.lt.64) iused(nsum+1)=0
+
+    syncave=0.
+    dtave=0.
+    fave=0.
+    if(nsum.gt.0) then
+       sym=sym/nsum
+       syncave=syncsum/nsum
+       dtave=dtsum/nsum
+       fave=float(nfsum)/nsum
+    endif
+
+    !  rewind 80
+    do i=1,nsave
+       csync='*'
+       if(flipsave(i).lt.0.0) csync='#'
+       if (associated (this%average_callback)) then
+          call this%average_callback(cused(i) .eq. '$',iutc(i),               &
+               syncsave(i) - 5.,dtsave(i),nfsave(i),flipsave(i) .lt.0.)
+       end if
+!       write(14,1000) cused(i),iutc(i),syncsave(i)-5.0,dtsave(i),nfsave(i),csync
+!1000   format(a1,i5.4,f6.1,f6.2,i6,1x,a1)
+    enddo
+
+    sqt=0.
+    sqf=0.
+    do j=1,64
+       i=iused(j)
+       if(i.eq.0) exit
+       csync='*'
+       if(flipsave(i).lt.0.0) csync='#'
+       !     write(80,3001) i,iutc(i),syncsave(i),dtsave(i),nfsave(i),csync
+       !3001 format(i3,i6.4,f6.1,f6.2,i6,1x,a1)
+       sqt=sqt + (dtsave(i)-dtave)**2
+       sqf=sqf + (nfsave(i)-fave)**2
+    enddo
+    rmst=0.
+    rmsf=0.
+    if(nsum.ge.2) then
+       rmst=sqrt(sqt/(nsum-1))
+       rmsf=sqrt(sqf/(nsum-1))
+    endif
+    !  write(80,3002)
+    !3002 format(16x,'----- -----')
+    !  write(80,3003) dtave,nint(fave)
+    !  write(80,3003) rmst,nint(rmsf)
+    !3003 format(15x,f6.2,i6)
+    !  flush(80)
+
+    !  nadd=nused*mode4
+    kbest=ich1
+    do k=ich1,ich2
+       call extract4(sym(1,k),ncount,avemsg)     !Do the Fano decode
+       nfanoave=0
+       if(ncount.ge.0) then
+          ichbest=k
+          nfanoave=nsum
+          go to 900
+       endif
+       if(nch(k).ge.mode4) exit
+    enddo
+
+    deepave='                      '
+    qave=0.
+
+    ! Possibly should pass nadd=nused, also ?
+    if(ndepth.ge.3) then
+       flipx=1.0                     !Normal flip not relevant for ave msg
+       qbest=0.
+       do k=ich1,ich2
+          call deep4(sym(2,k),neme,flipx,mycall,hiscall,hisgrid,deepave,qave)
+          !        write(82,3101) nutc,sym(51:53,k),flipx,k,qave,deepave
+          !3101    format(i4.4,4f8.1,i3,f7.2,2x,a22)
+          if(qave.gt.qbest) then
+             qbest=qave
+             deepbest=deepave
+             kbest=k
+             ndeepave=nsum
+          endif
+          if(nch(k).ge.mode4) exit
+       enddo
+
+       deepave=deepbest
+       qave=qbest
+       ichbest=kbest
+    endif
+
+900 return
+  end subroutine avg4
+end module jt4_decode
diff --git a/lib/jt4a.f90 b/lib/jt4a.f90
index cec80764f..fc37ec05c 100644
--- a/lib/jt4a.f90
+++ b/lib/jt4a.f90
@@ -1,44 +1,2 @@
-subroutine jt4a(dd,jz,nutc,nfqso,ntol0,emedelay,dttol,nagain,ndepth,     &
-     nclearave,minsync,minw,nsubmode,mycall,hiscall,hisgrid,nlist0,listutc0)
-
-  use jt4
-  use timer_module, only: timer
-
-  integer listutc0(10)
-  real*4 dd(jz)
-  real*4 dat(30*12000)
-  character*6 cfile6
-  character*12 mycall,hiscall
-  character*6 hisgrid
-
-  mode4=nch(nsubmode+1)
-  ntol=ntol0
-  neme=0
-  lumsg=6                         !### temp ? ###
-  ndiag=1
-  nlist=nlist0
-  listutc=listutc0
-
-! Lowpass filter and decimate by 2
-  call timer('lpf1    ',0)
-  call lpf1(dd,jz,dat,jz2)
-  call timer('lpf1    ',1)
-
-  i=index(MyCall,char(0))
-  if(i.le.0) i=index(MyCall,' ')
-  mycall=MyCall(1:i-1)//'            '
-  i=index(HisCall,char(0))
-  if(i.le.0) i=index(HisCall,' ')
-  hiscall=HisCall(1:i-1)//'            '
-
-  write(cfile6(1:4),1000) nutc
-1000 format(i4.4)
-  cfile6(5:6)='  '
-
-  call timer('wsjt4   ',0)
-  call wsjt4(dat,jz2,nutc,NClearAve,minsync,ntol,emedelay,dttol,mode4,minw, &
-       mycall,hiscall,hisgrid,nfqso,NAgain,ndepth,neme)
-  call timer('wsjt4   ',1)
-
-  return
-end subroutine jt4a
+  ! The contents of this file have been migrated to lib/jt4_decode.f90
+  
diff --git a/lib/jt65.f90 b/lib/jt65.f90
index 52e9f8716..7562fdd53 100644
--- a/lib/jt65.f90
+++ b/lib/jt65.f90
@@ -1,14 +1,14 @@
 program jt65
 
-! Test the JT65 decoder for WSJT-X
+  ! Test the JT65 decoder for WSJT-X
 
   use options
   use timer_module, only: timer
   use timer_impl, only: init_timer
+  use jt65_test
 
   character c
-  logical :: display_help=.false.
-  parameter (NZMAX=60*12000)
+  logical :: display_help=.false.,nrobust=.false.
   integer*4 ihdr(11)
   integer*2 id2(NZMAX)
   real*4 dd(NZMAX)
@@ -18,56 +18,54 @@ program jt65
   character*6 hisgrid
   equivalence (lenfile,ihdr(2))
   type (option) :: long_options(9) = [ &
-    option ('freq',.true.,'f','signal frequency, default FREQ=1270','FREQ'),         &
-    option ('help',.false.,'h','Display this help message',''),                      &
-    option ('ntrials',.true.,'n','number of trials, default TRIALS=10000','TRIALS'), &
-    option ('robust-sync',.false.,'r','robust sync',''),                             &
-    option ('my-call',.true.,'c','my callsign',''),                                  &
-    option ('his-call',.true.,'x','his callsign',''),                                &
-    option ('his-grid',.true.,'g','his grid locator',''),                            &
-    option ('experience-decoding',.true.,'X'                                         &
-            ,'experience decoding options (1..n), default FLAGS=0','FLAGS'),         &
-    option ('single-signal-mode',.false.,'s','decode at signal frequency only','') ]
+       option ('freq',.true.,'f','signal frequency, default FREQ=1270','FREQ'),         &
+       option ('help',.false.,'h','Display this help message',''),                      &
+       option ('ntrials',.true.,'n','number of trials, default TRIALS=10000','TRIALS'), &
+       option ('robust-sync',.false.,'r','robust sync',''),                             &
+       option ('my-call',.true.,'c','my callsign',''),                                  &
+       option ('his-call',.true.,'x','his callsign',''),                                &
+       option ('his-grid',.true.,'g','his grid locator',''),                            &
+       option ('experience-decoding',.true.,'X'                                         &
+               ,'experience decoding options (1..n), default FLAGS=0','FLAGS'),         &
+       option ('single-signal-mode',.false.,'s','decode at signal frequency only','') ]
 
-ntol=10
-nfqso=1270
-nagain=0
-nsubmode=0
-ntrials=10000
-nlow=200
-nhigh=4000
-n2pass=2
-nrobust=0
-nexp_decoded=0
-naggressive=1
+  ntol=10
+  nfqso=1270
+  nsubmode=0
+  ntrials=10000
+  nlow=200
+  nhigh=4000
+  n2pass=2
+  nexp_decoded=0
+  naggressive=0
 
   do
-    call getopt('f:hn:rc:x:g:X:s',long_options,c,optarg,narglen,nstat,noffset,nremain,.true.)
-    if( nstat .ne. 0 ) then
-      exit
-    end if
-    select case (c)
-      case ('f')
+     call getopt('f:hn:rc:x:g:X:s',long_options,c,optarg,narglen,nstat,noffset,nremain,.true.)
+     if( nstat .ne. 0 ) then
+        exit
+     end if
+     select case (c)
+     case ('f')
         read (optarg(:narglen), *) nfqso
-      case ('h')
+     case ('h')
         display_help = .true.
-      case ('n')
+     case ('n')
         read (optarg(:narglen), *) ntrials
-      case ('r')
-        nrobust=1
-      case ('c')
+     case ('r')
+        nrobust=.true.
+     case ('c')
         read (optarg(:narglen), *) mycall
-      case ('x')
+     case ('x')
         read (optarg(:narglen), *) hiscall
-      case ('g')
+     case ('g')
         read (optarg(:narglen), *) hisgrid
-      case ('X')
+     case ('X')
         read (optarg(:narglen), *) nexp_decoded
-      case ('s')
+     case ('s')
         nlow=nfqso-ntol
         nhigh=nfqso+ntol
         n2pass=1
-    end select
+     end select
   end do
 
   if(display_help .or. nstat.lt.0 .or. nremain.lt.1) then
@@ -79,17 +77,16 @@ naggressive=1
      print *, 'OPTIONS:'
      print *, ''
      do i = 1, size (long_options)
-       call long_options(i) % print (6)
+        call long_options(i) % print (6)
      end do
      go to 999
   endif
 
-  call init_timer()
+  call init_timer ('timer.out')
   call timer('jt65    ',0)
 
   ndecoded=0
   do ifile=noffset+1,noffset+nremain
-     newdat=1
      nfa=nlow
      nfb=nhigh
      minsync=0
@@ -106,24 +103,23 @@ naggressive=1
      call timer('read    ',1)
      dd(1:npts)=id2(1:npts)
      dd(npts+1:)=0.
-     call timer('jt65a   ',0)
 
-!     open(56,file='subtracted.wav',access='stream',status='unknown')
-!     write(56) ihdr(1:11)
+     !     open(56,file='subtracted.wav',access='stream',status='unknown')
+     !     write(56) ihdr(1:11)
 
-     call jt65a(dd,npts,newdat,nutc,nfa,nfb,nfqso,ntol,nsubmode, &
-                minsync,nagain,n2pass,nrobust,ntrials,naggressive,ndepth, &
-                mycall,hiscall,hisgrid,nexp_decoded,ndecoded)
-     call timer('jt65a   ',1)
+     call test(dd,nutc,nfa,nfb,nfqso,ntol,nsubmode, &
+          n2pass,nrobust,ntrials,naggressive, &
+          mycall,hiscall,hisgrid,nexp_decoded)
   enddo
 
   call timer('jt65    ',1)
   call timer('jt65    ',101)
-!  call four2a(a,-1,1,1,1)                  !Free the memory used for plans
-!  call filbig(a,-1,1,0.0,0,0,0,0,0)        ! (ditto)
+  !  call four2a(a,-1,1,1,1)                  !Free the memory used for plans
+  !  call filbig(a,-1,1,0.0,0,0,0,0,0)        ! (ditto)
   go to 999
 
 998 print*,'Cannot read from file:'
   print*,infile
 
-999 end program jt65
+999 continue
+end program jt65
diff --git a/lib/jt65_decode.f90 b/lib/jt65_decode.f90
index 2a236a2eb..5ce0bb26f 100644
--- a/lib/jt65_decode.f90
+++ b/lib/jt65_decode.f90
@@ -1,171 +1,212 @@
-subroutine jt65a(dd0,npts,newdat,nutc,nf1,nf2,nfqso,ntol,nsubmode,   &
-     minsync,nagain,n2pass,nrobust,ntrials,naggressive,ndepth,       &
-     mycall,hiscall,hisgrid,nexp_decode,ndecoded)
+module jt65_decode
 
-!  Process dd0() data to find and decode JT65 signals.
+  type :: jt65_decoder
+     procedure(jt65_decode_callback), pointer :: callback => null()
+   contains
+     procedure :: decode
+  end type jt65_decoder
 
-  use timer_module, only: timer
+  !
+  ! Callback function to be called with each decode
+  !
+  abstract interface
+     subroutine jt65_decode_callback (this, utc, sync, snr, dt, freq, drift,          &
+          decoded, ft, qual, candidates, tries, total_min, hard_min, aggression)
+       import jt65_decoder
+       implicit none
+       class(jt65_decoder), intent(inout) :: this
+       integer, intent(in) :: utc
+       real, intent(in) :: sync
+       integer, intent(in) :: snr
+       real, intent(in) :: dt
+       integer, intent(in) :: freq
+       integer, intent(in) :: drift
+       character(len=22), intent(in) :: decoded
+       integer, intent(in) :: ft
+       integer, intent(in) :: qual
+       integer, intent(in) :: candidates
+       integer, intent(in) :: tries
+       integer, intent(in) :: total_min
+       integer, intent(in) :: hard_min
+       integer, intent(in) :: aggression
+     end subroutine jt65_decode_callback
+  end interface
 
-  parameter (NSZ=3413,NZMAX=60*12000)
-  parameter (NFFT=1000)
-  real dd0(NZMAX)
-  real dd(NZMAX)
-  real ss(322,NSZ)
-  real savg(NSZ)
-  real a(5)
-  character*22 decoded,decoded0
-  character mycall*12,hiscall*12,hisgrid*6
-  type candidate
-     real freq
-     real dt
-     real sync
-  end type candidate
-  type(candidate) ca(300)
-  type decode
-     real freq
-     real dt
-     real sync
-     character*22 decoded
-  end type decode
-  type(decode) dec(50)
-  common/decstats/ntry65a,ntry65b,n65a,n65b,num9,numfano
-  common/steve/thresh0
-  common/test000/ncandidates,nhard_min,nsoft_min,nera_best,nsofter_min,   &
-       ntotal_min,ntry,nq1000,ntot         !### TEST ONLY ###
-  save
+contains
 
-  dd=dd0
-  ndecoded=0
-  do ipass=1,n2pass                             ! 2-pass decoding loop
-    newdat=1
-    if(ipass.eq.1) then                         !first-pass parameters
-      thresh0=2.5
-      nsubtract=1
-    elseif( ipass.eq.2 ) then !second-pass parameters
-      thresh0=2.5
-      nsubtract=0
-    endif
-    if(n2pass.lt.2) nsubtract=0
+  subroutine decode(this,callback,dd0,npts,newdat,nutc,nf1,nf2,nfqso,ntol,nsubmode,   &
+       minsync,nagain,n2pass,nrobust,ntrials,naggressive,ndepth,       &
+       mycall,hiscall,hisgrid,nexp_decode)
 
-!  if(newdat.ne.0) then
-     call timer('symsp65 ',0)
-     ss=0.
-     call symspec65(dd,npts,ss,nhsym,savg)    !Get normalized symbol spectra
-     call timer('symsp65 ',1)
-!  endif
-     nfa=nf1
-     nfb=nf2
-     if(naggressive.gt.0 .and. ntol.lt.1000) then
-        nfa=max(200,nfqso-ntol)
-        nfb=min(4000,nfqso+ntol)
-        thresh0=1.0
-     endif
+    !  Process dd0() data to find and decode JT65 signals.
 
-! nrobust = 0: use float ccf. Only if ncand>50 fall back to robust (1-bit) ccf
-! nrobust = 1: use only robust (1-bit) ccf
-    ncand=0
-    if(nrobust.eq.0) then
-      call timer('sync65  ',0)
-      call sync65(ss,nfa,nfb,naggressive,ntol,nhsym,ca,ncand,0)
-      call timer('sync65  ',1)
-    endif
-    if(ncand.gt.50) nrobust=1
-    if(nrobust.eq.1) then
-      ncand=0
-      call timer('sync65  ',0)
-      call sync65(ss,nfa,nfb,naggressive,ntol,nhsym,ca,ncand,1)
-      call timer('sync65  ',1)
-    endif
+    use timer_module, only: timer
 
-    call fqso_first(nfqso,ntol,ca,ncand)
+    include 'constants.f90'
+    parameter (NSZ=3413,NZMAX=60*12000)
+    parameter (NFFT=1000)
 
-    nvec=ntrials
-    if(ncand.gt.75) then
-!      write(*,*) 'Pass ',ipass,' ncandidates too large ',ncand
-      nvec=100
-    endif
+    class(jt65_decoder), intent(inout) :: this
+    procedure(jt65_decode_callback) :: callback
+    real, intent(in) :: dd0(NZMAX)
+    integer, intent(in) :: npts, nutc, nf1, nf2, nfqso, ntol     &
+         , nsubmode, minsync, n2pass, ntrials, naggressive, ndepth      &
+         , nexp_decode
+    logical, intent(in) :: newdat, nagain, nrobust
+    character(len=12), intent(in) :: mycall, hiscall
+    character(len=6), intent(in) :: hisgrid
 
-    df=12000.0/NFFT                     !df = 12000.0/8192 = 1.465 Hz
-    mode65=2**nsubmode
-    nflip=1                             !### temporary ###
-    nqd=0
-    decoded0=""
-    freq0=0.
+    real dd(NZMAX)
+    real ss(322,NSZ)
+    real savg(NSZ)
+    real a(5)
+    character*22 decoded,decoded0
+    type candidate
+       real freq
+       real dt
+       real sync
+    end type candidate
+    type(candidate) ca(300)
+    type accepted_decode
+       real freq
+       real dt
+       real sync
+       character*22 decoded
+    end type accepted_decode
+    type(accepted_decode) dec(50)
+    logical :: first_time, robust
+    common/decstats/ntry65a,ntry65b,n65a,n65b,num9,numfano
+    common/steve/thresh0
+    common/test000/ncandidates,nhard_min,nsoft_min,nera_best,nsofter_min,   &
+         ntotal_min,ntry,nq1000,ntot         !### TEST ONLY ###
+    save
 
-    do icand=1,ncand
-      freq=ca(icand)%freq
-      dtx=ca(icand)%dt
-      sync1=ca(icand)%sync
-      if(ipass.eq.1) ntry65a=ntry65a + 1
-      if(ipass.eq.2) ntry65b=ntry65b + 1
-      call timer('decod65a',0)
-      call decode65a(dd,npts,newdat,nqd,freq,nflip,mode65,nvec,     &
-           naggressive,ndepth,mycall,hiscall,hisgrid,nexp_decode,   &
-           sync2,a,dtx,nft,qual,nhist,decoded)
-      call timer('decod65a',1)
+    this%callback => callback
+    first_time=newdat
+    robust=nrobust
+    dd=dd0
+    ndecoded=0
+    do ipass=1,n2pass                             ! 2-pass decoding loop
+       first_time=.true.
+       if(ipass.eq.1) then                         !first-pass parameters
+          thresh0=2.5
+          nsubtract=1
+       elseif( ipass.eq.2 ) then !second-pass parameters
+          thresh0=2.5
+          nsubtract=0
+       endif
+       if(n2pass.lt.2) nsubtract=0
 
-!### Suppress false decodes in crowded HF bands ###
-      if(naggressive.eq.0 .and. ntrials.le.10000) then
-         if(ntry.eq.ntrials .or. ncandidates.eq.100) then
-            if(nhard_min.ge.42 .or. ntotal_min.ge.71) cycle
-         endif
-      endif
+       !  if(newdat) then
+       call timer('symsp65 ',0)
+       ss=0.
+       call symspec65(dd,npts,ss,nhsym,savg)    !Get normalized symbol spectra
+       call timer('symsp65 ',1)
+       !  endif
+       nfa=nf1
+       nfb=nf2
+       if(naggressive.gt.0 .and. ntol.lt.1000) then
+          nfa=max(200,nfqso-ntol)
+          nfb=min(4000,nfqso+ntol)
+          thresh0=1.0
+       endif
 
-      if(decoded.eq.decoded0 .and. abs(freq-freq0).lt. 3.0 .and.    &
-           minsync.ge.0) cycle                  !Don't display dupes
-      if(decoded.ne.'                      ' .or. minsync.lt.0) then
-        if( nsubtract .eq. 1 ) then
-           call timer('subtr65 ',0)
-           call subtract65(dd,npts,freq,dtx)
-           call timer('subtr65 ',1)
-        endif
-        nfreq=nint(freq+a(1))
-        ndrift=nint(2.0*a(2))
-        s2db=10.0*log10(sync2) - 35             !### empirical ###
-        nsnr=nint(s2db)
-        if(nsnr.lt.-30) nsnr=-30
-        if(nsnr.gt.-1) nsnr=-1
+       ! robust = .false.: use float ccf. Only if ncand>50 fall back to robust (1-bit) ccf
+       ! robust = .true. : use only robust (1-bit) ccf
+       ncand=0
+       if(.not.robust) then
+          call timer('sync65  ',0)
+          call sync65(ss,nfa,nfb,naggressive,ntol,nhsym,ca,ncand,0)
+          call timer('sync65  ',1)
+       endif
+       if(ncand.gt.50) robust=.true.
+       if(robust) then
+          ncand=0
+          call timer('sync65  ',0)
+          call sync65(ss,nfa,nfb,naggressive,ntol,nhsym,ca,ncand,1)
+          call timer('sync65  ',1)
+       endif
 
-! Serialize writes - see also decjt9.f90
-!$omp critical(decode_results) 
-        ndupe=0 ! de-dedupe
-        do i=1, ndecoded
-          if(decoded==dec(i)%decoded) then
-             ndupe=1
-             exit
+       call fqso_first(nfqso,ntol,ca,ncand)
+
+       nvec=ntrials
+       if(ncand.gt.75) then
+          !      write(*,*) 'Pass ',ipass,' ncandidates too large ',ncand
+          nvec=100
+       endif
+
+       df=12000.0/NFFT                     !df = 12000.0/8192 = 1.465 Hz
+       mode65=2**nsubmode
+       nflip=1                             !### temporary ###
+       nqd=0
+       decoded0=""
+       freq0=0.
+
+       do icand=1,ncand
+          freq=ca(icand)%freq
+          dtx=ca(icand)%dt
+          sync1=ca(icand)%sync
+          if(ipass.eq.1) ntry65a=ntry65a + 1
+          if(ipass.eq.2) ntry65b=ntry65b + 1
+          call timer('decod65a',0)
+          call decode65a(dd,npts,first_time,nqd,freq,nflip,mode65,nvec,     &
+               naggressive,ndepth,mycall,hiscall,hisgrid,nexp_decode,   &
+               sync2,a,dtx,nft,qual,nhist,decoded)
+          call timer('decod65a',1)
+
+          !### Suppress false decodes in crowded HF bands ###
+          if(naggressive.eq.0 .and. ntrials.le.10000) then
+             if(ntry.eq.ntrials .or. ncandidates.eq.100) then
+                if(nhard_min.ge.42 .or. ntotal_min.ge.71) cycle
+             endif
           endif
-        enddo
-        if(ndupe.ne.1 .or. minsync.lt.0) then
-          if(ipass.eq.1) n65a=n65a + 1
-          if(ipass.eq.2) n65b=n65b + 1
-          ndecoded=ndecoded+1
-          dec(ndecoded)%freq=freq+a(1)
-          dec(ndecoded)%dt=dtx
-          dec(ndecoded)%sync=sync2
-          dec(ndecoded)%decoded=decoded
-          nqual=min(qual,9999.0)
-!          if(nqual.gt.10) nqual=10
-          write(*,1010) nutc,nsnr,dtx-1.0,nfreq,decoded
-1010      format(i4.4,i4,f5.1,i5,1x,'#',1x,a22)
-          write(13,1012) nutc,nint(sync1),nsnr,dtx-1.0,float(nfreq),ndrift,  &
-             decoded,nft
-1012      format(i4.4,i4,i5,f6.1,f8.0,i4,3x,a22,' JT65',i4)
-          call flush(6)
-          call flush(13)
- !          write(79,3001) nutc,nint(sync1),nsnr,dtx-1.0,nfreq,ncandidates,    &
-           write(79,3001) nutc,sync1,nsnr,dtx-1.0,nfreq,ncandidates,    &
-                nhard_min,ntotal_min,ntry,naggressive,nft,nqual,decoded
- 3001      format(i4.4,f6.2,i4,f6.2,i5,i7,i3,i4,i8,i3,i2,i5,1x,a22)
-           flush(79)
-        endif
-        decoded0=decoded
-        freq0=freq
-        if(decoded0.eq.'                      ') decoded0='*'
-!$omp end critical(decode_results)
-      endif
-    enddo                                 !candidate loop
-    if(ndecoded.lt.1) exit
-  enddo                                   !two-pass loop
 
-  return
-end subroutine jt65a
+          if(decoded.eq.decoded0 .and. abs(freq-freq0).lt. 3.0 .and.    &
+               minsync.ge.0) cycle                  !Don't display dupes
+          if(decoded.ne.'                      ' .or. minsync.lt.0) then
+             if( nsubtract .eq. 1 ) then
+                call timer('subtr65 ',0)
+                call subtract65(dd,npts,freq,dtx)
+                call timer('subtr65 ',1)
+             endif
+             nfreq=nint(freq+a(1))
+             ndrift=nint(2.0*a(2))
+             s2db=10.0*log10(sync2) - 35             !### empirical ###
+             nsnr=nint(s2db)
+             if(nsnr.lt.-30) nsnr=-30
+             if(nsnr.gt.-1) nsnr=-1
+
+             ndupe=0 ! de-dedupe
+             do i=1, ndecoded
+                if(decoded==dec(i)%decoded) then
+                   ndupe=1
+                   exit
+                endif
+             enddo
+             if(ndupe.ne.1 .or. minsync.lt.0) then
+                if(ipass.eq.1) n65a=n65a + 1
+                if(ipass.eq.2) n65b=n65b + 1
+                ndecoded=ndecoded+1
+                dec(ndecoded)%freq=freq+a(1)
+                dec(ndecoded)%dt=dtx
+                dec(ndecoded)%sync=sync2
+                dec(ndecoded)%decoded=decoded
+                nqual=min(qual,9999.0)
+                !          if(nqual.gt.10) nqual=10
+                if (associated(this%callback)) then
+                   call this%callback(nutc,sync1,nsnr,dtx-1.0,nfreq,ndrift,decoded &
+                        ,nft,nqual,ncandidates,ntry,ntotal_min,nhard_min,naggressive)
+                end if
+             endif
+             decoded0=decoded
+             freq0=freq
+             if(decoded0.eq.'                      ') decoded0='*'
+          endif
+       enddo                                 !candidate loop
+       if(ndecoded.lt.1) exit
+    enddo                                   !two-pass loop
+
+    return
+  end subroutine decode
+
+end module jt65_decode
diff --git a/lib/jt9.f90 b/lib/jt9.f90
index 88c53486c..694c238e6 100644
--- a/lib/jt9.f90
+++ b/lib/jt9.f90
@@ -21,7 +21,7 @@ program jt9
   integer :: arglen,stat,offset,remain,mode=0,flow=200,fsplit=2700,          &
        fhigh=4000,nrxfreq=1500,ntrperiod=1,ndepth=60001,nexp_decode=0
   logical :: read_files = .true., tx9 = .false., display_help = .false.
-  type (option) :: long_options(22) = [ &
+  type (option) :: long_options(23) = [ &
     option ('help', .false., 'h', 'Display this help message', ''),          &
     option ('shmem',.true.,'s','Use shared memory for sample data','KEY'),   &
     option ('tr-period', .true., 'p', 'Tx/Rx period, default MINUTES=1',     &
@@ -49,6 +49,7 @@ program jt9
     option ('jt65', .false., '6', 'JT65 mode', ''),                          &
     option ('jt9', .false., '9', 'JT9 mode', ''),                            &
     option ('jt4', .false., '4', 'JT4 mode', ''),                            &
+    option ('sub-mode', .true., 'b', 'Sub mode, default SUBMODE=A', 'A'),    &
     option ('depth', .true., 'd',                                            &
         'JT9 decoding depth (1-3), default DEPTH=1', 'DEPTH'),               &
     option ('tx-jt9', .false., 'T', 'Tx mode is JT9', ''),                   &
@@ -67,8 +68,10 @@ program jt9
   common/decstats/ntry65a,ntry65b,n65a,n65b,num9,numfano
   data npatience/1/,nthreads/1/
 
+  nsubmode = 0
+
   do
-     call getopt('hs:e:a:r:m:p:d:f:w:t:964TL:S:H:c:G:x:g:X:',long_options,c,   &
+     call getopt('hs:e:a:b:r:m:p:d:f:w:t:964TL:S:H:c:G:x:g:X:',long_options,c,   &
           optarg,arglen,stat,offset,remain,.true.)
      if (stat .ne. 0) then
         exit
@@ -83,6 +86,8 @@ program jt9
            exe_dir = optarg(:arglen)
         case ('a')
            data_dir = optarg(:arglen)
+        case ('b')
+           nsubmode = ichar (optarg(:1)) - ichar ('A')
         case ('t')
            temp_dir = optarg(:arglen)
         case ('m')
@@ -236,10 +241,10 @@ program jt9
      enddo
      close(10)
      shared_data%params%nutc=nutc
-     shared_data%params%ndiskdat=1
+     shared_data%params%ndiskdat=.true.
      shared_data%params%ntr=60
      shared_data%params%nfqso=nrxfreq
-     shared_data%params%newdat=1
+     shared_data%params%newdat=.true.
      shared_data%params%npts8=74736
      shared_data%params%nfa=flow
      shared_data%params%nfsplit=fsplit
@@ -250,12 +255,11 @@ program jt9
      shared_data%params%ndepth=ndepth
      shared_data%params%dttol=3.
      shared_data%params%minsync=-1      !### TEST ONLY
-     shared_data%params%nfqso=1500      !### TEST ONLY
-     mycall="K1ABC       "  !### TEST ONLY
+     !mycall="K1ABC       "  !### TEST ONLY
      shared_data%params%naggressive=10
      shared_data%params%n2pass=1
      shared_data%params%nranera=8  ! ntrials=10000
-     shared_data%params%nrobust=0
+     shared_data%params%nrobust=.false.
      shared_data%params%nexp_decode=nexp_decode
      shared_data%params%mycall=mycall
      shared_data%params%mygrid=mygrid
@@ -274,9 +278,10 @@ program jt9
      else
         shared_data%params%nmode=mode
      end if
+     shared_data%params%nsubmode=nsubmode
      shared_data%params%datetime="2013-Apr-16 15:13" !### Temp
      if(mode.eq.9 .and. fsplit.ne.2700) shared_data%params%nfa=fsplit
-     call decoder(shared_data%ss,shared_data%id2,shared_data%params,nfsample)
+     call multimode_decoder(shared_data%ss,shared_data%id2,shared_data%params,nfsample)
   enddo
 
   call timer('jt9     ',1)
@@ -300,5 +305,4 @@ program jt9
   call filbig(a,-1,1,0.0,0,0,0,0,0)        !used for FFT plans
   call fftwf_cleanup_threads()
   call fftwf_cleanup()
-
 end program jt9
diff --git a/lib/jt9_decode.f90 b/lib/jt9_decode.f90
index 140f6e9d7..2704b4364 100644
--- a/lib/jt9_decode.f90
+++ b/lib/jt9_decode.f90
@@ -1,140 +1,162 @@
-subroutine decjt9(ss,id2,nutc,nfqso,newdat,npts8,nfa,nfsplit,nfb,ntol,  &
-     nzhsym,nagain,ndepth,nmode)
+module jt9_decode
 
-  use timer_module, only: timer
+  type :: jt9_decoder
+     procedure(jt9_decode_callback), pointer :: callback
+   contains
+     procedure :: decode
+  end type jt9_decoder
 
-  include 'constants.f90'
-  real ss(184,NSMAX)
-  character*22 msg
-  real*4 ccfred(NSMAX)
-  real*4 red2(NSMAX)
-  logical ccfok(NSMAX)
-  logical done(NSMAX)
-  integer*2 id2(NTMAX*12000)
-  integer*1 i1SoftSymbols(207)
-  common/decstats/ntry65a,ntry65b,n65a,n65b,num9,numfano
-  save ccfred,red2
+  abstract interface
+     subroutine jt9_decode_callback (this, utc, sync, snr, dt, freq, drift, decoded)
+       import jt9_decoder
+       implicit none
+       class(jt9_decoder), intent(inout) :: this
+       integer, intent(in) :: utc
+       real, intent(in) :: sync
+       integer, intent(in) :: snr
+       real, intent(in) :: dt
+       real, intent(in) :: freq
+       integer, intent(in) :: drift
+       character(len=22), intent(in) :: decoded
+     end subroutine jt9_decode_callback
+  end interface
 
-  nsynced=0
-  ndecoded=0
-  nsps=6912                                   !Params for JT9-1
-  df3=1500.0/2048.0
+contains
 
-  tstep=0.5*nsps/12000.0                      !Half-symbol step (seconds)
-  done=.false.
+  subroutine decode(this,callback,ss,id2,nutc,nfqso,newdat,npts8,nfa,nfsplit,nfb,ntol,  &
+       nzhsym,nagain,ndepth,nmode)
+    use timer_module, only: timer
 
-  nf0=0
-  nf1=nfa
-  if(nmode.eq.65+9) nf1=nfsplit
-  ia=max(1,nint((nf1-nf0)/df3))
-  ib=min(NSMAX,nint((nfb-nf0)/df3))
-  lag1=-int(2.5/tstep + 0.9999)
-  lag2=int(5.0/tstep + 0.9999)
-  if(newdat.ne.0) then
-     call timer('sync9   ',0)
-     call sync9(ss,nzhsym,lag1,lag2,ia,ib,ccfred,red2,ipk)
-     call timer('sync9   ',1)
-  endif
+    include 'constants.f90'
+    class(jt9_decoder), intent(inout) :: this
+    procedure(jt9_decode_callback) :: callback
+    real ss(184,NSMAX)
+    logical, intent(in) :: newdat, nagain
+    character*22 msg
+    real*4 ccfred(NSMAX)
+    real*4 red2(NSMAX)
+    logical ccfok(NSMAX)
+    logical done(NSMAX)
+    integer*2 id2(NTMAX*12000)
+    integer*1 i1SoftSymbols(207)
+    common/decstats/ntry65a,ntry65b,n65a,n65b,num9,numfano
+    save ccfred,red2
 
-  nsps8=nsps/8
-  df8=1500.0/nsps8
-  dblim=db(864.0/nsps8) - 26.2
+    this%callback => callback
+    nsynced=0
+    ndecoded=0
+    nsps=6912                                   !Params for JT9-1
+    df3=1500.0/2048.0
 
-  ia1=1                         !quel compiler gripe
-  ib1=1                         !quel compiler gripe
-  do nqd=1,0,-1
-     limit=5000
-     ccflim=3.0
-     red2lim=1.6
-     schklim=2.2
-     if(ndepth.eq.2) then
-        limit=10000
-        ccflim=2.7
-     endif
-     if(ndepth.ge.3 .or. nqd.eq.1) then
-        limit=30000
-        ccflim=2.5
-        schklim=2.0
-     endif
-     if(nagain.ne.0) then
-        limit=100000
-        ccflim=2.4
-        schklim=1.8
-     endif
-     ccfok=.false.
+    tstep=0.5*nsps/12000.0                      !Half-symbol step (seconds)
+    done=.false.
 
-     if(nqd.eq.1) then
-        nfa1=nfqso-ntol
-        nfb1=nfqso+ntol
-        ia=max(1,nint((nfa1-nf0)/df3))
-        ib=min(NSMAX,nint((nfb1-nf0)/df3))
-        ccfok(ia:ib)=(ccfred(ia:ib).gt.(ccflim-2.0)) .and.               &
-                     (red2(ia:ib).gt.(red2lim-1.0))
-        ia1=ia
-        ib1=ib
-     else
-        nfa1=nf1
-        nfb1=nfb
-        ia=max(1,nint((nfa1-nf0)/df3))
-        ib=min(NSMAX,nint((nfb1-nf0)/df3))
-        do i=ia,ib
-           ccfok(i)=ccfred(i).gt.ccflim .and. red2(i).gt.red2lim
-        enddo
-        ccfok(ia1:ib1)=.false.
-     endif
+    nf0=0
+    nf1=nfa
+    if(nmode.eq.65+9) nf1=nfsplit
+    ia=max(1,nint((nf1-nf0)/df3))
+    ib=min(NSMAX,nint((nfb-nf0)/df3))
+    lag1=-int(2.5/tstep + 0.9999)
+    lag2=int(5.0/tstep + 0.9999)
+    if(newdat) then
+       call timer('sync9   ',0)
+       call sync9(ss,nzhsym,lag1,lag2,ia,ib,ccfred,red2,ipk)
+       call timer('sync9   ',1)
+    endif
 
-     fgood=0.
-     do i=ia,ib
-        if(done(i) .or. (.not.ccfok(i))) cycle
-        f=(i-1)*df3
-        if(nqd.eq.1 .or.                                                   &
-           (ccfred(i).ge.ccflim .and. abs(f-fgood).gt.10.0*df8)) then
+    nsps8=nsps/8
+    df8=1500.0/nsps8
+    dblim=db(864.0/nsps8) - 26.2
 
-           call timer('softsym ',0)
-           fpk=nf0 + df3*(i-1)
-           call softsym(id2,npts8,nsps8,newdat,fpk,syncpk,snrdb,xdt,    &
-                freq,drift,a3,schk,i1SoftSymbols)
-           call timer('softsym ',1)
+    ia1=1                         !quel compiler gripe
+    ib1=1                         !quel compiler gripe
+    do nqd=1,0,-1
+       limit=5000
+       ccflim=3.0
+       red2lim=1.6
+       schklim=2.2
+       if(ndepth.eq.2) then
+          limit=10000
+          ccflim=2.7
+       endif
+       if(ndepth.ge.3 .or. nqd.eq.1) then
+          limit=30000
+          ccflim=2.5
+          schklim=2.0
+       endif
+       if(nagain) then
+          limit=100000
+          ccflim=2.4
+          schklim=1.8
+       endif
+       ccfok=.false.
 
-           sync=(syncpk+1)/4.0
-           if(nqd.eq.1 .and. ((sync.lt.0.5) .or. (schk.lt.1.0))) cycle
-           if(nqd.ne.1 .and. ((sync.lt.1.0) .or. (schk.lt.1.5))) cycle
+       if(nqd.eq.1) then
+          nfa1=nfqso-ntol
+          nfb1=nfqso+ntol
+          ia=max(1,nint((nfa1-nf0)/df3))
+          ib=min(NSMAX,nint((nfb1-nf0)/df3))
+          ccfok(ia:ib)=(ccfred(ia:ib).gt.(ccflim-2.0)) .and.               &
+               (red2(ia:ib).gt.(red2lim-1.0))
+          ia1=ia
+          ib1=ib
+       else
+          nfa1=nf1
+          nfb1=nfb
+          ia=max(1,nint((nfa1-nf0)/df3))
+          ib=min(NSMAX,nint((nfb1-nf0)/df3))
+          do i=ia,ib
+             ccfok(i)=ccfred(i).gt.ccflim .and. red2(i).gt.red2lim
+          enddo
+          ccfok(ia1:ib1)=.false.
+       endif
 
-           call timer('jt9fano ',0)
-           call jt9fano(i1SoftSymbols,limit,nlim,msg)
-           call timer('jt9fano ',1)
+       fgood=0.
+       do i=ia,ib
+          if(done(i) .or. (.not.ccfok(i))) cycle
+          f=(i-1)*df3
+          if(nqd.eq.1 .or.                                                   &
+               (ccfred(i).ge.ccflim .and. abs(f-fgood).gt.10.0*df8)) then
 
-           if(sync.lt.0.0 .or. snrdb.lt.dblim-2.0) sync=0.0
-           nsync=int(sync)
-           if(nsync.gt.10) nsync=10
-           nsnr=nint(snrdb)
-           ndrift=nint(drift/df3)
-           num9=num9+1
+             call timer('softsym ',0)
+             fpk=nf0 + df3*(i-1)
+             call softsym(id2,npts8,nsps8,newdat,fpk,syncpk,snrdb,xdt,    &
+                  freq,drift,a3,schk,i1SoftSymbols)
+             call timer('softsym ',1)
 
-           if(msg.ne.'                      ') then
-              numfano=numfano+1
+             sync=(syncpk+1)/4.0
+             if(nqd.eq.1 .and. ((sync.lt.0.5) .or. (schk.lt.1.0))) cycle
+             if(nqd.ne.1 .and. ((sync.lt.1.0) .or. (schk.lt.1.5))) cycle
 
-!$omp critical(decode_results) ! serialize writes - see also jt65a.f90
-              write(*,1000) nutc,nsnr,xdt,nint(freq),msg
-1000          format(i4.4,i4,f5.1,i5,1x,'@',1x,a22)
-              write(13,1002) nutc,nsync,nsnr,xdt,freq,ndrift,msg
-1002          format(i4.4,i4,i5,f6.1,f8.0,i4,3x,a22,' JT9')
-              call flush(6)
-              call flush(13)
-!$omp end critical(decode_results)
+             call timer('jt9fano ',0)
+             call jt9fano(i1SoftSymbols,limit,nlim,msg)
+             call timer('jt9fano ',1)
 
-              iaa=max(1,i-1)
-              ibb=min(NSMAX,i+22)
-              fgood=f
-              nsynced=1
-              ndecoded=1
-              ccfok(iaa:ibb)=.false.
-              done(iaa:ibb)=.true.
-           endif
-        endif
-     enddo
-     if(nagain.ne.0) exit
-  enddo
+             if(sync.lt.0.0 .or. snrdb.lt.dblim-2.0) sync=0.0
+             nsync=int(sync)
+             if(nsync.gt.10) nsync=10
+             nsnr=nint(snrdb)
+             ndrift=nint(drift/df3)
+             num9=num9+1
 
-  return
-end subroutine decjt9
+             if(msg.ne.'                      ') then
+                numfano=numfano+1
+                if (associated(this%callback)) then
+                   call this%callback(nutc,sync,nsnr,xdt,freq,ndrift,msg)
+                end if
+                iaa=max(1,i-1)
+                ibb=min(NSMAX,i+22)
+                fgood=f
+                nsynced=1
+                ndecoded=1
+                ccfok(iaa:ibb)=.false.
+                done(iaa:ibb)=.true.
+             endif
+          endif
+       enddo
+       if(nagain) exit
+    enddo
+
+    return
+  end subroutine decode
+end module jt9_decode
diff --git a/lib/jt9a.f90 b/lib/jt9a.f90
index d3a8e2e98..1482ec0d9 100644
--- a/lib/jt9a.f90
+++ b/lib/jt9a.f90
@@ -61,7 +61,7 @@ subroutine jt9a()
   local_params=shared_data%params !save a copy because wsjtx carries on accessing
   call flush(6)
   call timer('decoder ',0)
-  call decoder(shared_data%ss,shared_data%id2,local_params,12000)
+  call multimode_decoder(shared_data%ss,shared_data%id2,local_params,12000)
   call timer('decoder ',1)
 
 100 inquire(file=trim(temp_dir)//'/.lock',exist=fileExists)
diff --git a/lib/jt9com.f90 b/lib/jt9com.f90
index a0a63c03b..87cca58ac 100644
--- a/lib/jt9com.f90
+++ b/lib/jt9com.f90
@@ -1,4 +1,4 @@
-  use, intrinsic :: iso_c_binding, only: c_int, c_short, c_float, c_char
+  use, intrinsic :: iso_c_binding, only: c_int, c_short, c_float, c_char, c_bool
 
   include 'constants.f90'
 
@@ -7,10 +7,10 @@
   !
   type, bind(C) :: params_block
      integer(c_int) :: nutc
-     integer(c_int) :: ndiskdat
+     logical(c_bool) :: ndiskdat
      integer(c_int) :: ntr
      integer(c_int) :: nfqso
-     integer(c_int) :: newdat
+     logical(c_bool) :: newdat
      integer(c_int) :: npts8
      integer(c_int) :: nfa
      integer(c_int) :: nfsplit
@@ -19,7 +19,7 @@
      integer(c_int) :: kin
      integer(c_int) :: nzhsym
      integer(c_int) :: nsubmode
-     integer(c_int) :: nagain
+     logical(c_bool) :: nagain
      integer(c_int) :: ndepth
      integer(c_int) :: ntxmode
      integer(c_int) :: nmode
@@ -33,7 +33,7 @@
      integer(c_int) :: n2pass
      integer(c_int) :: nranera
      integer(c_int) :: naggressive
-     integer(c_int) :: nrobust
+     logical(c_bool) :: nrobust
      integer(c_int) :: nexp_decode
      character(kind=c_char, len=20) :: datetime
      character(kind=c_char, len=12) :: mycall
diff --git a/lib/softsym.f90 b/lib/softsym.f90
index 1e0867448..120fb6df9 100644
--- a/lib/softsym.f90
+++ b/lib/softsym.f90
@@ -6,6 +6,7 @@ subroutine softsym(id2,npts8,nsps8,newdat,fpk,syncpk,snrdb,xdt,        &
   use timer_module, only: timer
 
   parameter (NZ2=1512,NZ3=1360)
+  logical, intent(inout) :: newdat
   complex c2(0:NZ2-1)
   complex c3(0:NZ3-1)
   complex c5(0:NZ3-1)
diff --git a/lib/symspec.f90 b/lib/symspec.f90
index 75d23e2ae..8e3f143a1 100644
--- a/lib/symspec.f90
+++ b/lib/symspec.f90
@@ -60,7 +60,7 @@ subroutine symspec(shared_data,k,ntrperiod,nsps,ingain,nminw,pxdb,s,   &
      ja=0
      ssum=0.
      ihsym=0
-     if(shared_data%params%ndiskdat.eq.0) shared_data%id2(k+1:)=0   !Needed to prevent "ghosts". Not sure why.
+     if(.not. shared_data%params%ndiskdat) shared_data%id2(k+1:)=0   !Needed to prevent "ghosts". Not sure why.
   endif
   gain=10.0**(0.1*ingain)
   sq=0.