diff --git a/lib/decoder.f90 b/lib/decoder.f90
index ded53e3b8..37ca5b1bd 100644
--- a/lib/decoder.f90
+++ b/lib/decoder.f90
@@ -149,7 +149,7 @@ subroutine multimode_decoder(ss,id2,params,nfsample)
      go to 800
   endif
 
-  if(params%nmode.eq.-4) then
+  if(params%nmode.eq.5) then
      call timer('decft4  ',0)
      call my_ft4%decode(ft4_decoded,id2,params%nQSOProgress,params%nfqso,    &
           params%nutc,params%nfa,params%nfb,params%ndepth,ncontest,          &
diff --git a/lib/ft4/ft4sim.f90 b/lib/ft4/ft4sim.f90
index baf15fcb1..6b5d01599 100644
--- a/lib/ft4/ft4sim.f90
+++ b/lib/ft4/ft4sim.f90
@@ -111,18 +111,15 @@ program ft4sim
   c0((NN+1)*NSPS:(NN+2)*NSPS-1)=c0((NN+1)*NSPS:(NN+2)*NSPS-1)*(1.0+cos(twopi*(/(i,i=0,NSPS-1)/)/(2.0*NSPS) ))/2.0
   c0((NN+2)*NSPS:)=0.
 
-  k=nint((xdt+0.35)/dt)
+  k=nint((xdt+0.5)/dt)
   c0=cshift(c0,-k)
-  ia=k
 
   do ifile=1,nfiles
      c=c0
      if(fspread.ne.0.0 .or. delay.ne.0.0) call watterson(c,NZZ,NWAVE,fs,delay,fspread)
      c=sig*c
-  
-     ib=k
      wave=real(c)
-     peak=maxval(abs(wave(ia:ib)))
+     peak=maxval(abs(wave))
      nslots=1
    
      if(snrdb.lt.90) then
diff --git a/lib/ft4_decode.f90 b/lib/ft4_decode.f90
index e370b8996..effa11bf9 100644
--- a/lib/ft4_decode.f90
+++ b/lib/ft4_decode.f90
@@ -31,7 +31,7 @@ contains
     class(ft4_decoder), intent(inout) :: this
     procedure(ft4_decode_callback) :: callback
     parameter (NSS=NSPS/NDOWN)
-
+    parameter (NZZ=18*3456)
    character message*37,msgsent*37,msg0*37
    character c77*77
    character*37 decodes(100)
@@ -42,8 +42,8 @@ contains
    character*6 hhmmss
    character*4 cqstr,cqstr0
 
-   complex cd2(0:NMAX/NDOWN-1)                  !Complex waveform
-   complex cb(0:NMAX/NDOWN-1)
+   complex cd2(0:NZZ/NDOWN-1)                  !Complex waveform
+   complex cb(0:NZZ/NDOWN-1+NN*NSS)
    complex cd(0:NN*NSS-1)                       !Complex waveform
    complex ctwk(2*NSS),ctwk2(2*NSS,-16:16)
    complex csymb(NSS)
@@ -60,7 +60,7 @@ contains
    integer apbits(2*ND)
    integer apmy_ru(28),aphis_fd(28)
    integer icos4a(0:3),icos4b(0:3),icos4c(0:3),icos4d(0:3)
-   integer*2 iwave(NMAX)                 !Raw received data
+   integer*2 iwave(NZZ)                 !Raw received data
    integer*1 message77(77),rvec(77),apmask(2*ND),cw(2*ND)
    integer*1 hbits(2*NN)
    integer graymap(0:3)
@@ -216,7 +216,7 @@ contains
       snr=candidate(3,icand)-1.0
       call ft4_downsample(iwave,dobigfft,f0,cd2)  !Downsample to 32 Sam/Sym
       if(dobigfft) dobigfft=.false.
-      sum2=sum(cd2*conjg(cd2))/(real(NMAX)/real(NDOWN))
+      sum2=sum(cd2*conjg(cd2))/(real(NZZ)/real(NDOWN))
       if(sum2.gt.0.0) cd2=cd2/sqrt(sum2)
 ! Sample rate is now 12000/16 = 750 samples/second
       do isync=1,2
@@ -225,15 +225,14 @@ contains
             idfmax=12
             idfstp=3
             ibmin=0
-!            ibmax=216                     !Max DT = 216/750 = 0.288 s
-            ibmax=432
+            ibmax=800
             ibstp=4
          else
             idfmin=idfbest-4
             idfmax=idfbest+4
             idfstp=1
             ibmin=max(0,ibest-5)
-            ibmax=min(ibest+5,NMAX/NDOWN-1)
+            ibmax=min(ibest+5,NZZ/NDOWN-1)
             ibstp=1
          endif
          ibest=-1
@@ -462,7 +461,7 @@ contains
                xsnr=-20.0
             endif
             nsnr=nint(max(-20.0,xsnr))
-            xdt=ibest/750.0 - 0.45
+            xdt=ibest/750.0 - 0.5
             call this%callback(sync,nsnr,xdt,f0,message,iaptype,qual)
             if(ibest.ge.ibmax-15) msg0=message         !Possible dupe candidate
             exit
diff --git a/widgets/mainwindow.cpp b/widgets/mainwindow.cpp
index c21968906..2ab4342f9 100644
--- a/widgets/mainwindow.cpp
+++ b/widgets/mainwindow.cpp
@@ -2886,7 +2886,7 @@ void MainWindow::decode()                                       //decode()
   if(m_mode=="FT8") dec_data.params.lft8apon = ui->actionEnable_AP_FT8->isVisible () &&
       ui->actionEnable_AP_FT8->isChecked ();
   if(m_mode=="FT8") dec_data.params.napwid=50;
-  if(m_mode=="FT4") dec_data.params.nmode=-4;
+  if(m_mode=="FT4") dec_data.params.nmode=5;
   dec_data.params.ntrperiod=m_TRperiod;
   dec_data.params.nsubmode=m_nSubMode;
   if(m_mode=="QRA64") dec_data.params.nsubmode=100 + m_nSubMode;