Rik posted while I was still struggling to finish typing mine. If he had
been a bit faster or I had been a bit slower, I could have addressed some
part of the bandwidth issue. <g>
The necessary bandwidth of these methods may be correct as stated, but the
actual radiated bandwidths may not be. North American-style BPSK, a least
that which is generated in LowFER transmitters, is not particularly
spectrum-efficient. It's a constant-envelope type, which means it can be
amplified in high-efficiency stages (provided the output tuning isn't too
sharp). The extra sidebands are not a problem since we have 30kHz in which
to play, and negligible radiated power to start with. PSK31 gains its
spectrum efficiency through envelope shaping, but that same requirement
probably makes it a lot more susceptible to impulse noise than its
brute-force BPSK counterpart.
As I mentioned in my previous message, I agree with Rik's assessment that
narrower bandwidths with QRSS give us another window of opportunity for
communication below signal levels where pure digital modes fall over the
cliff edge. The window is not limitless, because propagation-related phase
shifts will eventually impact very narrow communication channels in the
analog domain too. Still, I think that window needs to be explored fully,
and not dismissed out of hand just because it's slower or lacks digital
purity.
73,
John
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