Message-ID: <41AE0BF6.2050408@freenet.de>
Date: Wed, 01 Dec 2004 19:22:46 +0100
From: Wolf DL4YHF <dl4yhf@freenet.de>
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To: RSGB LF Group <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Variable-PSK theory (warning - goes on a bit!)
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Hello Jim and group,

Thanks for the "Variable PSK" thoughts - will take some more time to
thing about them again.
We (that's Markus DF6NM and myself) came to similar conclusions that ...
- with an optimum-shaped "slow" phase transition you end up at MSK
- if one doesn't attempt to write the "ultimate (matched) decoder" for
MSK, it isn't sooo tough (but..)
- some clever ideas for synchronisation at very low symbol rates must be
implemented
(one of them being simply to synchronize it "manually" looking at a
radio-controlled clock).

As I see it, a fully automated digital mode which does "everything"
itself is not favourable compared to CW (oh but please don't let us
start debates on this again), and even QRSS / DFCW and other "visual"
modes have their charm - the operator's brain wants to be involved in
the decoding process.. but that's just a personal opinion.

As Brian wrote..

> So, in the absence of a narrow-band medium-speed keyboard 
mode that can be transmitted through a non-linear amplifier,
is it time to review how we make best use of our 2.1 kHz ??
<

Help may(!) be on the way, most likely a slow variant of G3PLX's PSK31 
in QPSK mode (which is already possible to send and decode), turned into 
MSK "somehow" to remove the need for a linear transmitter. This may be 
achieved by delaying the signal in the quadrature phase branch (of the 
modulator and demodulator) for a half symbol time, and shaping the 
pulses before the modulator. This way there will be no more 180° phase 
transitions in the modulated audio signal, only 90° phase changes, and 
the amplitude will be constant by means of the data pulse shaping.

I have no idea  if, when, and how  this will be implemented yet, it all 
depends...

Greetings,
Wolf DL4YHF .