WSJT-X/avemsg6m.f

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subroutine avemsg6m(s2db,nz,nslim,NFixLen,cfile6,lcum,
+ f0,lumsg,npkept)
C Attempts to find message length and then decodes an average message.
real s2db(0:43,nz)
real s2dc(0:43,22)
real wgt(22)
real acf(0:430)
logical lcum
character*43 pua
character*6 cfile6
character*22 avemsg,blanks
data pua/'0123456789., /#?$ABCDEFGHIJKLMNOPQRSTUVWXYZ'/
data blanks/' '/
data twopi/6.283185307/
data offset/20.6/
C Adjustable sig limit, depending on length of data to average.
nslim2=nslim - 9 + 4.0*log10(624.0/nz) !### +10 was here
k=0
sum=0.
nsum=0
do j=1,nz
if(mod(j,3).eq.1) then
sum=sum+s2db(0,j) !Measure avg sig strength for sync tone
nsum=nsum+1
else
k=k+1
call move(s2db(0,j),s2db(0,k),44) !Save data spectra
endif
enddo
sig=sum/nsum !Signal strength estimate
nsig=nint(db(sig)-offset)
C Most of the time in this routine is in this loop.
kz=k
do lag=0,kz-1
sum=0.
do j=1,kz-lag
do i=0,43
sum=sum+s2db(i,j)*s2db(i,j+lag)
enddo
enddo
acf(lag)=sum
enddo
acf0=acf(0)
do lag=0,kz-1
acf(lag)=acf(lag)/acf0
enddo
lmsg1=NFixLen/256
lmsg2=NFixLen-256*lmsg1
if(mod(lmsg1,2).eq.1) lmsg1=lmsg1+1
if(mod(lmsg2,2).eq.1) lmsg2=lmsg2+1
smax=-1.e9
do ip=4,22,2 !Compute periodogram for allowed msg periods
if(NFixLen.ne.0 .and. ip.ne.4 .and. ip.ne.lmsg1
+ .and. ip.ne.lmsg2) go to 5
f=1.0/ip
s=0.
do lag=0,kz-1
s=s+acf(lag)*cos(twopi*f*lag)
enddo
if(s.gt.smax) then
smax=s
msglen=ip !Save best message length
endif
5 enddo
C Average the symbols from s2db into s2dc.
call zero(s2dc,44*22)
call zero(wgt,22)
do j=1,kz
k=mod(j-1,msglen)+1
call add(s2db(0,j),s2dc(0,k),s2dc(0,k),44)
wgt(k)=wgt(k)+1.0
enddo
do j=1,msglen !Hard-decode the avg msg,
smax=-1.e9 !picking max bin for each char
do i=1,43
s2dc(i,j)=s2dc(i,j)/wgt(j)
if(s2dc(i,j).gt.smax) then
smax=s2dc(i,j)
ipk=i
endif
enddo
k=mod(ipk,3)
i=ipk
avemsg(j:j)=pua(i:i)
enddo
ndf0=nint(f0-1076.66)
do i=1,msglen
if(avemsg(i:i).eq.' ') goto 10
enddo
go to 20
10 avemsg=avemsg(i+1:msglen)//avemsg(1:i)
20 if(nsig.gt.nslim2) then
npkept=npkept+1
avemsg=avemsg(1:msglen)//blanks
write(lumsg,1020) cfile6,nsig,ndf0,avemsg,msglen
if(lcum) write(21,1020) cfile6,nsig,ndf0,avemsg,msglen
1020 format(a6,8x,i6,i5,7x,a22,19x,'*',i4)
endif
return
end