Improve dt estimation in ft8b so that dt refinement procedure in subtractft8.f90 can be done with 4 calls to sqf instead of 7.

lib/ft8/ft8b.f90

@@ -17,6 +17,7 @@ subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,nzhsym,lapon,     &
   real bmeta(174),bmetb(174),bmetc(174),bmetd(174)
   real llra(174),llrb(174),llrc(174),llrd(174),llrz(174)           !Soft symbols
   real dd0(15*12000)
+  real ss(9)
   integer*1 message77(77),apmask(174),cw(174)
   integer apsym(58),aph10(10)
   integer mcq(29),mcqru(29),mcqfd(29),mcqtest(29),mcqww(29)
@@ -28,6 +29,7 @@ subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,nzhsym,lapon,     &
   integer ncontest,ncontest0
   logical one(0:511,0:8)
   integer graymap(0:7)
+  integer iloc(1)
   complex cd0(0:3199)
   complex ctwk(32)
   complex csymb(32)
@@ -106,17 +108,15 @@ subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,nzhsym,lapon,     &
 
   i0=nint((xdt+0.5)*fs2)                   !Initial guess for start of signal
   smax=0.0
-  do idt=i0-8,i0+8                         !Search over +/- one quarter symbol
+  do idt=i0-10,i0+10                         !Search over +/- one quarter symbol
      call sync8d(cd0,idt,ctwk,0,sync)
      if(sync.gt.smax) then
         smax=sync
         ibest=idt
      endif
   enddo
-  xdt2=ibest*dt2                           !Improved estimate for DT
 
 ! Now peak up in frequency
-  i0=nint(xdt2*fs2)
   smax=0.0
   do ifr=-5,5                              !Search over +/- 2.5 Hz
     delf=ifr*0.5
@@ -126,7 +126,7 @@ subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,nzhsym,lapon,     &
       ctwk(i)=cmplx(cos(phi),sin(phi))
       phi=mod(phi+dphi,twopi)
     enddo
-    call sync8d(cd0,i0,ctwk,1,sync)
+    call sync8d(cd0,ibest,ctwk,1,sync)
     if( sync .gt. smax ) then
       smax=sync
       delfbest=delf
@@ -135,9 +135,22 @@ subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,nzhsym,lapon,     &
   a=0.0
   a(1)=-delfbest
   call twkfreq1(cd0,NP2,fs2,a,cd0)
-  xdt=xdt2
   f1=f1+delfbest                           !Improved estimate of DF
-  call sync8d(cd0,i0,ctwk,0,sync)
+
+  call timer('ft8_down',0)
+  call ft8_downsample(dd0,.false.,f1,cd0)   !Mix f1 to baseband and downsample
+  call timer('ft8_down',1)
+
+  smax=0.0
+  do idt=-4,4                         !Search over +/- one quarter symbol
+     call sync8d(cd0,ibest+idt,ctwk,0,sync)
+     ss(idt+5)=sync
+  enddo
+  smax=maxval(ss)
+  iloc=maxloc(ss)
+  ibest=iloc(1)-5+ibest
+  xdt=(ibest-1)*dt2
+  sync=smax
 
   do k=1,NN
     i1=ibest+(k-1)*32
@@ -421,7 +434,7 @@ subroutine ft8b(dd0,newdat,nQSOProgress,nfqso,nftx,ndepth,nzhsym,lapon,     &
      if(lsubtract) call subtractft8(dd0,itone,f1,xdt,.false.)
 !     write(21,3001) nzhsym,npasses,nqsoprogress,ipass,iaptype,lsubtract,   &
 !          f1,xdt,msg37(1:22); flush(21)
-!3001 format(5i3,L3,f7.1,f7.2,2x,a22)
+!3001 format(5i3,L3,f7.1,f9.4,2x,a22)
      xsig=0.0
      xnoi=0.0
      do i=1,79

lib/ft8/subtractft8.f90

@@ -41,19 +41,24 @@ subroutine subtractft8(dd0,itone,f0,dt,ldt)
   call gen_ft8wave(itone,79,1920,2.0,12000.0,f0,cref,xjunk,1,NFRAME)
 
   if(ldt) then                         !Are we refining DT ?
-     sqa=sqf(-300)
+!     sqa=sqf(-300)
-     sqb=sqf(300)
+!     sqb=sqf(300)
-     sq0=sqf(0)                        !Do the subtraction with idt=0
+!     sq0=sqf(0)                        !Do the subtraction with idt=0
-     call peakup(sqa,sq0,sqb,dx)
+!     call peakup(sqa,sq0,sqb,dx)
-     if(abs(dx).gt.1.0) return         !No acceptable minimum: do not subtract
+!     if(abs(dx).gt.1.0) return         !No acceptable minimum: do not subtract
-     i1=nint(300.0*dx)                 !First approximation of best idt
+!     i1=nint(300.0*dx)                 !First approximation of best idt
-     sqa=sqf(i1-60)
+i1=0
-     sqb=sqf(i1+60)
+!     sqa=sqf(i1-60)
+!     sqb=sqf(i1+60)
+     sqa=sqf(i1-90)
+     sqb=sqf(i1+90)
      sq0=sqf(i1)
      call peakup(sqa,sq0,sqb,dx)
      if(abs(dx).gt.1.0) return         !No acceptable minimum: do not subtract
-     i2=nint(60.0*dx) + i1             !Best estimate of idt
+!     i2=nint(60.0*dx) + i1             !Best estimate of idt
+     i2=nint(90.0*dx) + i1             !Best estimate of idt
      sq0=sqf(i2)                       !Do the subtraction with idt=i2
+!write(*,*) 'subtract - i2= ',i2,dt
   else
      sq0=sqf(0)                        !Do the subtraction with idt=0
   endif

lib/ft8/sync8.f90

@@ -106,7 +106,7 @@ subroutine sync8(dd,nfa,nfb,syncmin,nfqso,maxcand,s,candidate,   &
      if(red(n).lt.syncmin.or.isnan(red(n)).or.k.eq.maxcand) exit
      k=k+1
      candidate0(1,k)=n*df
-     candidate0(2,k)=(jpeak(n)-1)*tstep
+     candidate0(2,k)=(jpeak(n)-0.5)*tstep
      candidate0(3,k)=red(n)
   enddo
   ncand=k
@@ -144,5 +144,6 @@ subroutine sync8(dd,nfa,nfb,syncmin,nfqso,maxcand,s,candidate,   &
      endif
   enddo
   ncand=k-1
+
   return
 end subroutine sync8

lib/ft8/sync8d.f90

@@ -12,20 +12,16 @@ subroutine sync8d(cd0,i0,ctwk,itwk,sync)
   integer icos7(0:6)
   data icos7/3,1,4,0,6,5,2/
   data first/.true./
-  save first,twopi,fs2,dt2,taus,baud,csync
+  save first,twopi,csync
 
   p(z1)=real(z1)**2 + aimag(z1)**2          !Statement function for power
 
 ! Set some constants and compute the csync array.  
   if( first ) then
     twopi=8.0*atan(1.0)
-    fs2=12000.0/NDOWN                       !Sample rate after downsampling
-    dt2=1/fs2                               !Corresponding sample interval
-    taus=32*dt2                             !Symbol duration
-    baud=1.0/taus                           !Keying rate
     do i=0,6
       phi=0.0
-      dphi=twopi*icos7(i)*baud*dt2  
+      dphi=twopi*icos7(i)/32.0 
       do j=1,32
         csync(i,j)=cmplx(cos(phi),sin(phi)) !Waveform for 7x7 Costas array
         phi=mod(phi+dphi,twopi)