Hi Steve,
Thanks for sharing some further comparisons of kvasd and sfrsd.
When WSJT-X was first being expanded from a testbed for JT9 to a more
capable, more general program for HF DXing, JT65A capability was added
to make the program attractive to the large existing user base for that
mode. The JT65 demodulation/decoding chain was brought over from
WSJT10, more or less intact; but some quick changes were made that
helped to provide smooth "bi-lingual" operation when signals of both
modes were in the same passband.
You're now discovering some of the ways in which those quick integration
decisions affected JT65 decoding performance. At the time I was mainly
interested in JT65 performance that was fast and "good enough" for use
at HF (where nearly all QSOs are made at signal levels at least several
dB above the JT65A threshold, around -24 dB). Several types of
fine-tuning are now done differently in WSJT10 and WSJT-X. With some
effort I could probably reconstruct the motivation for each of these
differences, but it's probably better now to just say there is every
good reason to look such considerations again, and to make different
choices when good reasons are found.
I made a quick test this morning that illustrates a sizable difference
in JT65 decoding performance between WSJT10 and WSJT-X -- in this case,
for marginal signals on an AWGN channel.
I generated 1000 files with JT65A signals at -24 dB S/N, using SimJT.
(I think this is exactly what you have done?) The present "stock"
decoder in WSJT-X decodes 189/1000 of these -- a result that I think is
consistent with your recent tests. WSJT10 decoded 809/1000 of the test
files, and it's also considerably faster. Neither program produced any
false decodes.
I guess I should now try WSJT-X+sfrsd on the same set of test files.
-- Joe, K1JT
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