John:
I am not going to speculate on what will be in 100 years from now, what I
can address is to put some realism to the PSK31 claims and observations.
PSK31 is a rather neat implementation of DSP technology that was known and
well understood 30 plus years ago. It builds on some of the DSP development
work that has made the analogue MODEMS we use so very fast and cheap. PSK31
has no magic, if your trying to hear PSK31 with its ~30Hz bandwidth in an FM
or SSB wide filter then you are giving PSK a hugh advantage that is not
consistent. With my 30Hz DSP filter here I will hear any PSK signal anytime
just as well as the DSP in the sound card hears it. PSK31 depends very much
on the frequency stability of the transmitting medium, that is why is fails
so quickly and totally when it arrives via an auroral reflected path which
messes of the frequency component.
For EME the signals has to content with frequency, phase, and amplitude
distortions that play heck with the EME signal. Since Mr.. Shannon set down
the rules so many years ago we now only have significant opportunities to
improve the situation by using integration techniques to recover signals
over a period of time. Periods of Time over which to take a decision on the
presence of a signal or the non presence of a signal has lots of potential,
but this potential will take some years to be realized. As you can guess
the bit rates of such a system will be very slow, which is ok for EME but of
no use for voice or any form of real time communications.
In the interim all we have is the human ear to work with, to present the ear
with the best we can simulate normal hearing by for instance rolling a
signal over the edge of a filter and "finding" the signal for the first
time. At this time, many EME operators are able to hear 10 to 15 db or more
below what PSK31 has to offer at its very best. The human ear is a
phenomenal detector given good training and skill development. That is the
good news, the bad news is that the human ear is a lousy integrator beyond a
small part of a second. The eye is vastly better as a signal integrator
which is why highly optimized DSP based waterfall type displays can let one
see a signal that one will never hear aurally.
Summary: PSK31 is good, a bit better than some of the earlier digital
modes. It is not a signal processing breakthrough and offers no magic
capability that was not known 30 or more years ago.
73
Larry, VA3LK
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