From 766c97870937c3ca854f8d2bd33c340751c805a6 Mon Sep 17 00:00:00 2001
From: Steven Franke <s.j.franke@icloud.com>
Date: Sun, 25 Sep 2016 20:37:30 +0000
Subject: [PATCH] Make frequency search more efficient in msk144 realtime
 decoder.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7111 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
---
 lib/makepings.f90         |  4 ++--
 lib/msk144decodeframe.f90 |  3 +--
 lib/msk144spd.f90         |  4 ++--
 lib/msk144sync.f90        | 11 +++++++----
 lib/mskrtd.f90            |  4 ++--
 5 files changed, 14 insertions(+), 12 deletions(-)

diff --git a/lib/makepings.f90 b/lib/makepings.f90
index 68220a41c..1e2b12d2a 100644
--- a/lib/makepings.f90
+++ b/lib/makepings.f90
@@ -6,8 +6,8 @@ subroutine makepings(pings,npts,width,sig)
 
   iping0=-999
   dt=1.0/12000.0
-  do i=1,14,2
-     t0(i)=i                            !Make pings at t=1, 3, ... 13 s.
+  do i=1,14
+     t0(i)=i                            !Make pings at t=1, 2, ... 14 s.
   enddo
   w=width
   amp=sig
diff --git a/lib/msk144decodeframe.f90 b/lib/msk144decodeframe.f90
index a8f89a8b6..3e74cccbd 100644
--- a/lib/msk144decodeframe.f90
+++ b/lib/msk144decodeframe.f90
@@ -87,13 +87,12 @@ subroutine msk144decodeframe(c,msgreceived,nsuccess)
   ssig=sqrt(s2av-sav*sav)
   softbits=softbits/ssig
 
-  sigma=0.72
+  sigma=0.75
   llr(1:48)=softbits(9:9+47)
   llr(49:128)=softbits(65:65+80-1)
   llr=2.0*llr/(sigma*sigma)
   
   max_iterations=10
-  max_dither=1
 !  call timer('bpdec144 ',0)
   call bpdecode144(llr,max_iterations,decoded,niterations)
 !  call timer('bpdec144 ',1)
diff --git a/lib/msk144spd.f90 b/lib/msk144spd.f90
index a3f8ff355..f8c6c5ec3 100644
--- a/lib/msk144spd.f90
+++ b/lib/msk144spd.f90
@@ -154,7 +154,7 @@ subroutine msk144spd(cbig,n,ntol,nsuccess,msgreceived,fc,fret,tret)
   msgreceived=' '
   npeaks=2
   ntol0=8
-  ndf=2
+  deltaf=2.0
   do icand=1,ndet  ! Try to sync/demod/decode each candidate.
     ib=max(1,nstart(icand)-NSPM)
     ie=ib-1+3*NSPM
@@ -166,7 +166,7 @@ subroutine msk144spd(cbig,n,ntol,nsuccess,msgreceived,fc,fret,tret)
     fo=fc+ferrs(icand)
     do iav=1,NPATTERNS
       navmask=navpatterns(1:3,iav) 
-      call msk144sync(cdat,3,ntol0,ndf,navmask,npeaks,fo,fest,npkloc,nsyncsuccess,c)
+      call msk144sync(cdat,3,ntol0,deltaf,navmask,npeaks,fo,fest,npkloc,nsyncsuccess,c)
 
       if( nsyncsuccess .eq. 0 ) cycle
 
diff --git a/lib/msk144sync.f90 b/lib/msk144sync.f90
index 754f450f5..12fa3ef4e 100644
--- a/lib/msk144sync.f90
+++ b/lib/msk144sync.f90
@@ -1,4 +1,4 @@
-subroutine msk144sync(cdat,nframes,ntol,ndf,navmask,npeaks,fc,fest,npklocs,nsuccess,c)
+subroutine msk144sync(cdat,nframes,ntol,delf,navmask,npeaks,fc,fest,npklocs,nsuccess,c)
 
   parameter (NSPM=864)
   complex cdat(NSPM*nframes)
@@ -55,8 +55,11 @@ subroutine msk144sync(cdat,nframes,ntol,ndf,navmask,npeaks,fc,fest,npklocs,nsucc
   xmax=0.0
   bestf=0.0
   n=nframes*NSPM
-  do ifr=-ntol,ntol,ndf            !Find freq that maximizes sync
-     ferr=ifr
+  nf=nint(ntol/delf)
+  fac=1.0/(48.0*sqrt(float(navg)))
+
+  do ifr=-nf,nf            !Find freq that maximizes sync
+     ferr=ifr*delf
      call tweak1(cdat,n,-(fc+ferr),cdat2)
      c=0
      do i=1,nframes
@@ -75,7 +78,7 @@ subroutine msk144sync(cdat,nframes,ntol,ndf,navmask,npeaks,fc,fest,npklocs,nsucc
      enddo
 
      xcc=abs(cc)
-     xb=maxval(xcc)/(48.0*sqrt(float(navg)))
+     xb=maxval(xcc)*fac
      if(xb.gt.xmax) then
         xmax=xb
         bestf=ferr
diff --git a/lib/mskrtd.f90 b/lib/mskrtd.f90
index 123fe834a..8a725ca77 100644
--- a/lib/mskrtd.f90
+++ b/lib/mskrtd.f90
@@ -99,9 +99,9 @@ subroutine mskrtd(id2,nutc0,tsec,ntol,nrxfreq,line)
   do iavg=1,NPATTERNS
      iavmask=iavpatterns(1:8,iavg)
      navg=sum(iavmask)
-     ndf=nint(7.0/navg) 
+     deltaf=7.0/real(navg)  ! search increment for frequency sync
      npeaks=2
-     call msk144sync(cdat(1:8*NSPM),8,ntol,ndf,iavmask,npeaks,fc,fest,npkloc,nsyncsuccess,c)
+     call msk144sync(cdat(1:8*NSPM),8,ntol,deltaf,iavmask,npeaks,fc,fest,npkloc,nsyncsuccess,c)
      if( nsyncsuccess .eq. 0 ) cycle
 
      do ipk=1,npeaks