WSJT-X/demod64a.f

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subroutine demod64a(signal,nadd,mrsym,mrprob,
+ mr2sym,mr2prob,ntest,nlow)
C Demodulate the 64-bin spectra for each of 63 symbols in a frame.
C Parameters
C nadd number of spectra already summed
C mrsym most reliable symbol value
C mr2sym second most likely symbol value
C mrprob probability that mrsym was the transmitted value
C mr2prob probability that mr2sym was the transmitted value
implicit real*8 (a-h,o-z)
real*4 signal(64,63)
real*8 fs(64)
integer mrsym(63),mrprob(63),mr2sym(63),mr2prob(63)
afac=1.1 * float(nadd)**0.64
scale=255.999
C Compute average spectral value
sum=0.
do j=1,63
do i=1,64
sum=sum+signal(i,j)
enddo
enddo
ave=sum/(64.*63.)
C Compute probabilities for most reliable symbol values
do j=1,63
s1=-1.e30
fsum=0.
do i=1,64
x=min(afac*signal(i,j)/ave,50.d0)
fs(i)=exp(x)
fsum=fsum+fs(i)
if(signal(i,j).gt.s1) then
s1=signal(i,j)
i1=i !Most reliable
endif
enddo
s2=-1.e30
do i=1,64
if(i.ne.i1 .and. signal(i,j).gt.s2) then
s2=signal(i,j)
i2=i !Second most reliable
endif
enddo
p1=fs(i1)/fsum !Normalized probabilities
p2=fs(i2)/fsum
mrsym(j)=i1-1
mr2sym(j)=i2-1
mrprob(j)=scale*p1
mr2prob(j)=scale*p2
enddo
sum=0.
nlow=0
do j=1,63
sum=sum+mrprob(j)
if(mrprob(j).le.5) nlow=nlow+1
enddo
ntest=sum/63
return
end