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From: Roger Lapthorn <rogerlapthorn@gmail.com>
Date: Tue, 10 Jan 2017 20:02:17 +0000
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To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Wideband EbNaut with prefix?
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Hi Paul,

My health is still far from good and I have never tried EbNaut, but I
wonder if this would be good for earth-mode? With QRSS3 6km was my limit
some years ago. I ran out of test sites but feel sure further would have
been possible. Then my stroke got in the way!

73s
Roger G3XBM

On 8 January 2017 at 23:17, Paul Nicholson <vlf0403@abelian.org> wrote:

>
> A decode from a near field test at VLF:
>
>  Rank 6938 Eb/N0 -0.4 dB 8K19A 60 chars
>
> The interesting thing is, the symbol period is 6.25 milliseconds
> (3152 symbols for 19.7 second total duration) and the message
> was sent by magnetic coupling between two undisciplined
> soundcards.  Received against the natural VLF background.
> The message was also 'unannounced'.
>
> EbNaut here is sending a coded prefix.  The decoder monitors
> a band and searches for prefixes, then measures the frequency
> and timing accurately enough to decode the following message
> coherently.
>
> It relies on the undisciplined soundcard clock or RX LO being
> stable over the message duration, say up to a minute or so.
>
> The overhead of the prefix is at the moment 1.25dB, hoping to
> bring that down a bit.  A delicate matter of balancing the
> prefix energy and message energy.  No point in a detectable
> prefix if the message wont decode, or vice versa.
>
> In principle then, with a small Eb/N0 overhead, the decoder can
> take a live untimed I/Q stream from SpecLab or your favourite
> SDR and monitor a band a few Hz wide. The only thing you have
> to know in advance is the symbol rate.  Coding in the prefix
> supplies the rest.
>
> No good of course for slow narrow band, but there might be
> applications for short duration wide band messages coherently
> detected and decoded with signals a dB or so from the limit.
>
> --
> Paul Nicholson
> --
>
>

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<div dir=3D"ltr"><div>Hi Paul,</div><div><br></div><div>My health is still =
far from good and I have never tried EbNaut, but=C2=A0I wonder if this woul=
d be good for earth-mode? With QRSS3 6km was my limit some years ago. I ran=
 out of test sites but feel sure further would have been possible. Then my =
stroke got in the way!</div><div><br></div><div>73s</div><div>Roger G3XBM</=
div></div><div class=3D"gmail_extra"><br><div class=3D"gmail_quote">On 8 Ja=
nuary 2017 at 23:17, Paul Nicholson <span dir=3D"ltr">&lt;<a href=3D"mailto=
:vlf0403@abelian.org" target=3D"_blank">vlf0403@abelian.org</a>&gt;</span> =
wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;bord=
er-left:1px #ccc solid;padding-left:1ex"><br>
A decode from a near field test at VLF:<br>
<br>
=C2=A0Rank 6938 Eb/N0 -0.4 dB 8K19A 60 chars<br>
<br>
The interesting thing is, the symbol period is 6.25 milliseconds<br>
(3152 symbols for 19.7 second total duration) and the message<br>
was sent by magnetic coupling between two undisciplined<br>
soundcards.=C2=A0 Received against the natural VLF background.<br>
The message was also &#39;unannounced&#39;.<br>
<br>
EbNaut here is sending a coded prefix.=C2=A0 The decoder monitors<br>
a band and searches for prefixes, then measures the frequency<br>
and timing accurately enough to decode the following message<br>
coherently.<br>
<br>
It relies on the undisciplined soundcard clock or RX LO being<br>
stable over the message duration, say up to a minute or so.<br>
<br>
The overhead of the prefix is at the moment 1.25dB, hoping to<br>
bring that down a bit.=C2=A0 A delicate matter of balancing the<br>
prefix energy and message energy.=C2=A0 No point in a detectable<br>
prefix if the message wont decode, or vice versa.<br>
<br>
In principle then, with a small Eb/N0 overhead, the decoder can<br>
take a live untimed I/Q stream from SpecLab or your favourite<br>
SDR and monitor a band a few Hz wide. The only thing you have<br>
to know in advance is the symbol rate.=C2=A0 Coding in the prefix<br>
supplies the rest.<br>
<br>
No good of course for slow narrow band, but there might be<br>
applications for short duration wide band messages coherently<br>
detected and decoded with signals a dB or so from the limit.<br>
<br>
--<br>
Paul Nicholson<br>
--<br>
<br>
</blockquote></div><br></div>

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