Date: Sat, 12 Dec 2015 17:37:21 -0330 (NST)
From: jcraig@mun.ca
To: rsgb_lf_group@blacksheep.org
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Message-ID: <Pine.LNX.4.64.1512121733200.322@plato.ucs.mun.ca>
References: <566B6B8A.3020505@abelian.org> <8D3032BBD104B12-628-31A99A@webmail-vm001.sysops.aol.com>
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Subject: Re: LF: VO1NA - carrier 0900 - 1200 UTC
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Hi Markus,

You are most welcome.  Thank-you for the detailed reports on the
signals and the interesting commentary.  I'll be busy reading
for a while!

A signal to VK7 is a fond dream and with more radials and luck
it will be a reality.

Thanks to all and Happy Marconi Transatlantic Aniversary to
all.

Joe VO1NA

On Sat, 12 Dec 2015, Markus Vester wrote:

> Hi Joe, Paul,
> =C2=A0
> here's my three day's worth... Going from 2 to=C2=A05 minute averaging se=
emed to produce fewer cycle slips, and=C2=A0the best-fit average frequency =
was now=C2=A0around -0.144 mHz. As my calibration is only good to +-0.1 mHz=
, this is=C2=A0in good agreement with Paul's=C2=A0GPS-referenced=C2=A0-0.19=
 mHz average.
> =C2=A0
> Thanks Joe for this interesting experiment! Would it=C2=A0make sense to p=
ut the carrier back on for a couple of hours each day for Edgar, during the=
 common darkness period to Tasmania?
> =C2=A0
> All the best,
> Markus
> =C2=A0
> (DF6NM in JN59NJ)
> =C2=A0
> =C2=A0
> -----Urspr=C3=BCngliche Mitteilung-----
> Von: Paul Nicholson &lt;vlf0403@abelian.org&gt;
> An: rsgb_lf_group &lt;rsgb_lf_group@blacksheep.org&gt;
> Verschickt: Sa, 12 Dez 2015 1:37 am
> Betreff: Re: LF: VO1NA - carrier 0900 - 1200 UTC
>
> =C2=A0
> Well done Joe, epic 3-day transmission and good data.
>
> The full plot
>
>  http://abelian.org/vlf/tmp/151212a.png
>
> The diurnal doesn't repeat very well from day to day but
> diurnals often don't.   But it appears mostly diurnal as
> opposed to oscillator drift and it looks like the long term
> stability of the tx is very good.
>
> For comparison here is 24kHz NAA over the same time period
>
>  http://abelian.org/vlf/tmp/151212b.png
>
> There's enough data here to draw some tentative conclusion.
>
> NAA diurnal is much more repeatable and its dark path phase
> varies by no more than 50 degrees.  At 8kHz signal phase is
> even steadier on long paths.  But at LF the variation is much
> more, roughly in proportion to the frequency as we might expect.
>
> If this is generally the case at LF and it probably is, it
> doesn't bode well for the sort of ultra narrow band coherent
> BPSK that works so well at VLF where we use message durations
> of up to several hours.  We're just not seeing that kind of
> window here.
>
> When signals are so weak that the reference phase must be found
> by trial and error, it's quite easy to guess the phase when
> it's likely to be steady or nearly so - not many trials are
> needed. But guessing becomes impractical if the phase wanders
> about, too many phase patterns must be tried [*].
>
> It looks from these measurements that the narrow band signaling
> that works well at VLF will not work at LF.   The longest
> duration we could use is probably around 60 to 90 minutes.
>
> On the other hand, LF signals are much stronger than VLF signals
> and the noise floor is lower so wide band high speed BPSK
> might do well and phase guessing works fine when the message
> duration is not too long.  If the message is rapid enough,
> the phase is going to be approximately steady whatever the
> propagation is doing.
>
> Maybe the boundaries to push above VLF are going to be with
> high speed messages, perhaps at higher frequencies because
> 137 isn't wide enough.
>
> Operation would still be around 0dB Eb/N0, aiming for the
> channel capacity, but at a much higher rates and with stronger
> signals.
>
> So, 1mS symbols, anyone?
>
> [*] Not just impractical: increasing the number of phase trials
> reduces the overall coding gain because it increases the chance
> of a false detection.
>
> --=20
> Paul Nicholson
> --=C2=A0
> =C2=A0
> =C2=A0
> =C2=A0
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