First cut at identifying multiple candidates for decoding. Needs work.

lib/ft4/ft4_decode.f90

@@ -64,16 +64,16 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
    candidate=0.0
    ncand=0
 
-   nfa=375
-   nfb=3000
-   syncmin=1.0
+   fa=375.0
+   fb=3000.0
+   syncmin=1.2
    maxcand=100
 !      call syncft4(iwave,nfa,nfb,syncmin,nfqso,maxcand,s,candidate,ncand,sbase)
 
-   call getcandidates4(iwave,375.0,3000.0,0.2,2200.0,100,savg,candidate,ncand,sbase)
+   call getcandidates4(iwave,fa,fb,syncmin,nfqso,100,savg,candidate,ncand,sbase)
    ndecodes=0
    do icand=1,ncand
-      f0=candidate(1,icand)-35.0
+      f0=candidate(1,icand)
       xsnr=10*log10(candidate(3,icand))-15.0
       if( f0.le.375.0 .or. f0.ge.(5000.0-375.0) ) cycle
       call ft4_downsample(iwave,f0,cd2) ! downsample from 320 Sa/Symbol to 20 Sa/Symbol
@@ -81,26 +81,43 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
       if(sum2.gt.0.0) cd2=cd2/sqrt(sum2)
 
 ! 750 samples/second here
+
+      do isync=1,2
+         if(isync.eq.1) then
+            idfmin=-50
+            idfmax=50
+            idfstp=3
+            ibmin=0
+            ibmax=374
+            ibstp=4
+         else
+            idfmin=idfbest-5
+            idfmax=idfbest+5
+            idfstp=1
+            ibmin=max(0,ibest-5)
+            ibmax=min(ibest+5,NMAX/NDOWN-1)
+            ibstp=1
+         endif   
          ibest=-1
          smax=-99.
-      dfbest=-1.
-      do idf=-30,+30,2
-         df=idf
+         idfbest=0
+         do idf=idfmin,idfmax,idfstp
             a=0.
-         a(1)=df
+            a(1)=real(idf)
             ctwk=1.
             call twkfreq1(ctwk,4*NSS,fs,a,ctwk2)
-         do istart=0,374
+            do istart=ibmin,ibmax,ibstp
                call sync4d(cd2,istart,ctwk2,1,sync)
                if(sync.gt.smax) then
                   smax=sync
                   ibest=istart
-               dfbest=df
+                  idfbest=idf
                endif
             enddo
          enddo
+      enddo
 
-      f0=f0+dfbest
+      f0=f0+real(idfbest)
       call ft4_downsample(iwave,f0,cb) ! downsample from 320s/Symbol to 20s/Symbol
       sum2=sum(abs(cb)**2)/(real(NSS)*NN)
       if(sum2.gt.0.0) cb=cb/sqrt(sum2)
@@ -111,7 +128,6 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
          call four2a(csymb,NSS,1,-1,1)
          cs(0:3,k)=csymb(1:4)
          s4(0:3,k)=abs(csymb(1:4))
-!write(*,'(i4,4f8.1)') k, s4(0:3,k)
       enddo
 
 ! sync quality check
@@ -189,6 +205,10 @@ subroutine ft4_decode(cdatetime0,nfqso,iwave,ndecodes,mycall,hiscall,nrx,line)
       ns4=count(hbits(199:206).eq.(/0,0,0,1,1,0,1,1/))
       nsync_qual=ns1+ns2+ns3+ns4
 
+      if(nsync.lt.8 .or. nsync_qual.lt. 20) then
+         cycle
+      endif 
+
       scalefac=2.83
       llra(  1: 58)=bmeta(  9: 66)
       llra( 59:116)=bmeta( 75:132)

lib/ft4/getcandidates4.f90

@@ -10,6 +10,7 @@ subroutine getcandidates4(id,fa,fb,syncmin,nfqso,maxcand,savg,candidate,   &
   real candidate(3,maxcand)
   integer*2 id(NMAX)
   integer indx(NH1)
+  integer ipk(1)
   equivalence (x,cx)
 
 ! Compute symbol spectra, stepping by NSTEP steps.  
@@ -29,8 +30,8 @@ subroutine getcandidates4(id,fa,fb,syncmin,nfqso,maxcand,savg,candidate,   &
      savg=savg + s(1:NH1,j)                   !Average spectrum
   enddo
   savsm=0.
-  do i=6,NH1-5
-    savsm(i)=sum(savg(i-5:i+5))/11.
+  do i=8,NH1-7
+    savsm(i)=sum(savg(i-7:i+7))/15.
   enddo
   nfa=fa/df
   nfb=fb/df
@@ -39,22 +40,22 @@ subroutine getcandidates4(id,fa,fb,syncmin,nfqso,maxcand,savg,candidate,   &
   call indexx(savsm(nfa:nfb),np,indx)
   xn=savsm(nfa+indx(nint(0.3*np)))
   savsm=savsm/xn
-  imax=-1
-  xmax=-99.
-  do i=2,NH1-1
-    if(savsm(i).gt.savsm(i-1).and.    &
-       savsm(i).gt.savsm(i+1).and.    &
-       savsm(i).gt.xmax) then
-      xmax=savsm(i) 
-      imax=i
-    endif
-  enddo
-  f0=imax*df
-  if(xmax.gt.1.2) then
+
+  ncand=0
+  f_offset = -1.5*12000/512
+  do i=1,maxcand
+     ipk=maxloc(savsm(nfa:nfb))
+     ip=nfa-1+ipk(1)
+     xmax=savsm(ip)
+     savsm(max(1,ip-8):min(NH1,ip+8))=0.0
+     if(xmax.ge.syncmin) then
         ncand=ncand+1
-     candidate(1,ncand)=f0
+        candidate(1,ncand)=ip*df+f_offset 
         candidate(2,ncand)=-99.9
         candidate(3,ncand)=xmax
+     else
+        exit
      endif
+  enddo
 return
 end subroutine getcandidates4