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From: Andy Talbot <andy.g4jnt@gmail.com>
Date: Thu, 6 Sep 2018 14:25:23 +0100
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To: LineOne <rsgb_lf_group@blacksheep.org>,
        rsgb_lf_group <rsgb_lf_group@yahoogroups.co.uk>
Subject: Re: LF: Slow JT9 modes...
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And a follow-on thought ...

Wonder if a waterfall plot that shows phase of each bin as colour instead
of amplitude would be any use as a simple signalling scheme
May try that with my custom LF receiver...

http://g4jnt.com/Coherent_LF_Receiver.pdf    It hasn't had a great deal of
use since I built it - now may be the time to revisit

Andy
www.g4jnt.com


On 6 September 2018 at 14:21, Andy Talbot <andy.g4jnt@gmail.com> wrote:

> As good as JT9 is, in whatever speed-flavour, at LF it throws away one
> aspect of LF propagation that isn't not really availalble for HF, phase
> stability over longer periods, at least suited to a few characters.   JT9
> is a purely power-based system with heavy FEC.
>
> So while slower versions of JT9 would be good for LF in  the short term,
> they will not make the most of what propagation can offer.  NO one on the
> WSJT-X development team is interested in LF, so it's no good looking
> there.    However, I'm sure they'd be amenable to someone else joining the
> team and adding an LF users perspective and writing / developing the
> relevant submodes.   Or do it independently using the open-source code.
>
> EBnaut carries phase signalling to the extreme, carrying no sync / timing
> info in the on-air symbols and being completely reliant on high stability
> frequency sources and people accurately starting and stopping.   This
> complex manual setting is, in my opinion its downfall;  high stability
> sources are less of a problem these days as OCXOs are now so cheap and
> readily availalble.
>
> What we need is an intermediate slow PSK or QPSK based scheme that carries
> its own timing and sync.   FEC is something that could come later, we first
> of all want a simple PSK decoder scheme that search over a modest span in
> frequency - say 0.2Hz and with unknown timing .   I suggest differential
> BPSK as a stat, where the data depends on teh phase change from one symbol
> to the next.   That removes the need for absolute clock recovery, and also,
> provided tuning error is appreciably lesss than symbol rate, even for
> carrier recovery.   Just compare one block of digitised data (of a symbol's
> length) witjh the previous one and look for a peak every so often to get
> the boundary .  Some framing will be needed in order to guarantee a few
> phase changes for alignment.
>
> A block / timed scheme like WSJT would probably work best as it reduces
> the searching for sync.  It also makes the soundcard driving software
> easier as a fixed length block can be recorded to a .WAV file more easily
> than continuous real time data reading from the s-card.
>
> Once the signalling and signal recovery is proven, then is the time to
> think about adding FEC but even a none error-corrected scheme ought to have
> a fair bit to offer in testing.
>
> The only real downside to PSK is its spectrum is you switch rapidly.   But
> its no worse than on-off keying, and if the signal is being generated by
> upconverting from a soundcard phase ramping could perhaps be used to reduce
> sidebands
>
>
>
>
>
> Andy
> www.g4jnt.com
>
>
>
>

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<div dir=3D"ltr"><div dir=3D"ltr">And a follow-on thought ...<div><br></div=
><div>Wonder if a waterfall plot that shows phase of each bin as colour ins=
tead of amplitude would be any use as a simple signalling scheme</div><div>=
May try that with my custom LF receiver...</div><div><br></div><div><a href=
=3D"http://g4jnt.com/Coherent_LF_Receiver.pdf">http://g4jnt.com/Coherent_LF=
_Receiver.pdf</a>=C2=A0 =C2=A0 It hasn&#39;t had a great deal of use since =
I built it - now may be the time to revisit<br></div></div></div><div class=
=3D"gmail_extra"><br clear=3D"all"><div><div class=3D"gmail_signature" data=
-smartmail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"ltr"><div>=
<div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr">Andy<div><span=
 style=3D"font-size:12.8px"><a href=3D"http://www.g4jnt.com" target=3D"_bla=
nk">www.g4jnt.com</a></span><br></div><div><br></div></div></div></div></di=
v></div></div></div></div></div></div></div>
<br><div class=3D"gmail_quote">On 6 September 2018 at 14:21, Andy Talbot <s=
pan dir=3D"ltr">&lt;<a href=3D"mailto:andy.g4jnt@gmail.com" target=3D"_blan=
k">andy.g4jnt@gmail.com</a>&gt;</span> wrote:<br><blockquote class=3D"gmail=
_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:=
1ex"><div dir=3D"ltr">As good as JT9 is, in whatever speed-flavour, at LF i=
t throws away one aspect of LF propagation that isn&#39;t not really availa=
lble for HF, phase stability over longer periods, at least suited to a few =
characters.=C2=A0 =C2=A0JT9 is a purely power-based system with heavy FEC.<=
div><br></div><div>So while slower versions of JT9 would be good for LF in=
=C2=A0 the short term, they will not make the most of what propagation can =
offer.=C2=A0 NO one on the WSJT-X development team is interested in LF, so =
it&#39;s no good looking there.=C2=A0 =C2=A0 However, I&#39;m sure they&#39=
;d be amenable to someone else joining the team and adding an LF users pers=
pective and writing / developing the relevant submodes.=C2=A0 =C2=A0Or do i=
t independently using the open-source code.=C2=A0=C2=A0<br><div><br></div><=
div>EBnaut carries phase signalling to the extreme, carrying no sync / timi=
ng info in the on-air symbols and being completely reliant on high stabilit=
y frequency sources and people accurately starting and stopping.=C2=A0 =C2=
=A0This complex manual setting is, in my opinion its downfall;=C2=A0 high s=
tability sources are less of a problem these days as OCXOs are now so cheap=
 and readily availalble.</div><div><br></div><div>What we need is an interm=
ediate slow PSK or QPSK based scheme that carries its own timing and sync.=
=C2=A0 =C2=A0FEC is something that could come later, we first of all want a=
 simple PSK decoder scheme that search over a modest span in frequency - sa=
y 0.2Hz and with unknown timing .=C2=A0 =C2=A0I suggest differential BPSK a=
s a stat, where the data depends on teh phase change from one symbol to the=
 next.=C2=A0 =C2=A0That removes the need for absolute clock recovery, and a=
lso, provided tuning error is appreciably lesss than symbol rate, even for =
carrier recovery.=C2=A0 =C2=A0Just compare one block of digitised data (of =
a symbol&#39;s length) witjh the previous one and look for a peak every so =
often to get the boundary .=C2=A0 Some framing will be needed in order to g=
uarantee a few phase changes for alignment.</div><div><br></div><div>A bloc=
k / timed scheme like WSJT would probably work best as it reduces the searc=
hing for sync.=C2=A0 It also makes the soundcard driving software easier as=
 a fixed length block can be recorded to a .WAV file more easily than conti=
nuous real time data reading from the s-card.</div><div><br></div><div>Once=
 the signalling and signal recovery is proven, then is the time to think ab=
out adding FEC but even a none error-corrected scheme ought to have a fair =
bit to offer in testing.</div><div><br></div><div>The only real downside to=
 PSK is its spectrum is you switch rapidly.=C2=A0 =C2=A0But its no worse th=
an on-off keying, and if the signal is being generated by upconverting from=
 a soundcard phase ramping could perhaps be used to reduce sidebands</div><=
div><br></div><div>=C2=A0<br><div><br></div><div><br><div class=3D"gmail_ex=
tra"><br clear=3D"all"><div><div class=3D"m_-2562814904326467309gmail_signa=
ture" data-smartmail=3D"gmail_signature"><div dir=3D"ltr"><div><div dir=3D"=
ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr"><div><div dir=3D"ltr">Andy=
<div><span style=3D"font-size:12.8px"><a href=3D"http://www.g4jnt.com" targ=
et=3D"_blank">www.g4jnt.com</a></span><br></div><div><br></div></div></div>=
</div></div></div></div></div></div></div></div></div>
<br><div class=3D"gmail_quote"><br></div></div></div></div></div></div>
</blockquote></div><br></div>

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