diff --git a/lib/qra/q65/q65.f90 b/lib/qra/q65/q65.f90
index 2012af83f..9f89fa2e7 100644
--- a/lib/qra/q65/q65.f90
+++ b/lib/qra/q65/q65.f90
@@ -437,11 +437,16 @@ subroutine q65_ccf_22(s1,iz,jz,nfqso,ntol,ndepth,ntrperiod,iavg,ipk,jpk,  &
 
   ia=max(nfa,100)/df
   ib=min(nfb,4900)/df
-  max_drift=0
-  if(nqd.eq.1 .and. iavg.eq.0 .and. ntol.le.100 .and. ntrperiod.eq.60) then
+  max_drift=0                         !Drift units: bins/TxT
+! Do we need a GUI control to set max_drift ?
+! For now, turn on drift compensation only for submodes 15B amd 60A.  
+  if(nqd.eq.1 .and. iavg.eq.0 .and. ntol.le.100 .and. ntrperiod.eq.60 .and. &
+       mode_q65.eq.1) max_drift=10    !Q65-60A
+  if(nqd.eq.1 .and. iavg.eq.0 .and. ntol.le.100 .and. ntrperiod.eq.15 .and. &
+       mode_q65.eq.4) max_drift=40    !Q65-15C
+  if(max_drift.ne.0) then
      ia=nint((nfqso-ntol)/df)
      ib=nint((nfqso+ntol)/df)
-     max_drift=10                        !Drift units: bins/TRperiod (?)
   endif
 
   do i=ia,ib
diff --git a/lib/qra/q65/q65_loops.f90 b/lib/qra/q65/q65_loops.f90
index 424a5de91..a1bcc64cb 100644
--- a/lib/qra/q65/q65_loops.f90
+++ b/lib/qra/q65/q65_loops.f90
@@ -52,6 +52,7 @@ subroutine q65_loops(c00,npts2,nsps2,nsubmode,ndepth,jpk0,    &
      if(mod(idf,2).eq.0) ndf=-ndf
      a=0.
      a(1)=-(f0+0.5*baud*ndf)
+! Variable 'drift' is frequency increase over full TxT.  Therefore we want:
      a(2)=-0.5*drift
      call twkfreq(c00,c0,npts2,6000.0,a)
      do idt=1,idtmax
diff --git a/lib/test_q65.f90 b/lib/test_q65.f90
index 4135a290d..e2987d719 100644
--- a/lib/test_q65.f90
+++ b/lib/test_q65.f90
@@ -1,6 +1,6 @@
 program test_q65
 
-  character*82 cmd1,cmd2,line
+  character*84 cmd1,cmd2,line
   character*22 msg
   character*8 arg
   character*1 csubmode
@@ -71,8 +71,8 @@ program test_q65
   tsym=1.0/baud
 
 !                1         2         3         4         5         6         7
-!       123456789012345678901234567890123456789012345678901234567890123456789012345'
-  cmd1='q65sim   "K1ABC W9XYZ EN37      " A 1500  5.0  0.0 0.0  1  60  100   -10.0 > junk0'
+!       1234567890123456789012345678901234567890123456789012345678901234567890123456'
+  cmd1='q65sim   "K1ABC W9XYZ EN37      " A 1500  5.0  0.0   0.0  1  60  100   -10.0 > junk0'
   cmd2='jt9 -3 -p  15 -L 300 -H 3000 -d   3 -b A -Q 3 -f 1500 *.wav > junk'
 
   write(cmd1(10:33),'(a)') '"'//msg//'"'
@@ -80,10 +80,10 @@ program test_q65
   write(cmd1(37:40),'(i4)') nf0
   write(cmd1(41:45),'(f5.0)') fDop
   write(cmd1(46:50),'(f5.2)') dt
-  write(cmd1(51:54),'(f4.0)') f1
-  write(cmd1(55:57),'(i3)') nstp
-  write(cmd1(58:61),'(i4)') ntrperiod
-  write(cmd1(62:66),'(i5)') nfiles
+  write(cmd1(51:56),'(i6)') nint(f1)
+  write(cmd1(57:59),'(i3)') nstp
+  write(cmd1(60:63),'(i4)') ntrperiod
+  write(cmd1(64:68),'(i5)') nfiles
 
   write(cmd2(11:13),'(i3)') ntrperiod
   write(cmd2(33:35),'(i3)') ndepth
@@ -94,7 +94,7 @@ program test_q65
   call system('rm -f *.wav')
 
   write(*,1008) ntrperiod,csubmode,ndepth,fDop,f1,nstp
-1008 format('Mode:',i4,a1,'  Depth:',i3,'  fDop:',f6.1,'  Drift:',f6.1,  &
+1008 format('Mode:',i4,a1,'  Depth:',i3,'  fDop:',f6.1,'  Drift:',f8.1,  &
           '  Steps:',i3)
   write(*,1010) (j,j=0,5)
   write(12,1010) (j,j=0,5)
@@ -112,7 +112,7 @@ program test_q65
      nfalse=0
      naptype=0
      ndecn=0
-     write(cmd1(70:74),'(f5.1)') snr1
+     write(cmd1(72:76),'(f5.1)') snr1
      call system(cmd1)
      call sec0(0,tdec)
      call system(cmd2)
diff --git a/lib/twkfreq.f90 b/lib/twkfreq.f90
index 7c240d529..5188d5006 100644
--- a/lib/twkfreq.f90
+++ b/lib/twkfreq.f90
@@ -1,5 +1,9 @@
 subroutine twkfreq(c3,c4,npts,fsample,a)
 
+  ! Adjust frequency of complex data
+  ! a(1)    Hz
+  ! a(2)    Hz/(0.5*TxT), where TxT = npts/fsample = file duration
+  
   complex c3(npts)
   complex c4(npts)
   complex w,wstep