Hi Joe,
I have found a reason for this issue: if dt value in decode65a.f90 is negative
and too low we are getting out of the dd() array.
Simple string
'if(dt.lt.xxx) return'
completely resolved this issue, there is no broken information symbols anymore
coming to decoders and symbol probability being calculated properly in the
demod64a.f90 now.
73 Igor UA3DJY
Re: [wsjt-devel] broken first five JT65 information symbols, WSJT-X From: Joe
Taylor <joe@pr...> - 2016-05-19 13:22:17
Hi Igor,
Thank you for your careful scrutiny of internal behavior of the JT65
decoder, and for pointing out what you imagine could be a problem.
I believe there is nothing wrong.
Under certain circumstances the values p1=0 and p2=0 may occur.
Variable psum is prevented from having a zero value by line 39 in
demod64a.f90, not because of "Fortran accuracy". Later calculations of
p1/p2 do not cause problems because the actual calculation is
effectively p1/(p2+0.01) -- see line 130 in ftrsd2/c. Symbols affected
by these calculations are effectively "erased", so they do not cause
false decodes.
-- 73, Joe, K1JT
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