Message-ID: <001d01c2a633$d31d7060$0700000a@parissn2>
From: "Stewart Nelson" <sn@scgroup.com>
To: rsgb_lf_group@blacksheep.org
References: <000b01c2a4ff$bc781fc0$ea00a8c0@f3a3a2> <000601c2a50e$0b89ca60$4d6a0450@oemcomputer> <3DFDE74B.7725145F@diolog.de> <5.1.0.14.0.20021217140941.029d9210@gemini.herts.ac.uk>
Date: Wed, 18 Dec 2002 02:21:42 +0100
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Subject: Re: LF: Re: QSO format
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Hi Jim and all,

Well, I admit to not having any solid data on the subject,
and was hoping to get some feedback from the propagation
experts here.

The HBG signal would not be used to predict the absolute
phase of G3AQC, but only changes in the propagation delay.
The quadrature signal from G3AQC would be rotated according
to the received HBG phase, and the resulting complex signal
integrated.  The final decode would be performed based
on the phase recovered from the integrated result.  How
this is done would depend on the modulation used; for CW,
choosing the angle with maximum total energy would probably
be adequate.  So the phase only has to roughly track, most
of the time.  If you are off by, say, 30 degrees, that's
just a 1.25 dB loss.

There will occasionally be huge phase discrepancies, when
one signal is nearly canceled because two effective paths
are roughly 180 degrees apart.  But I believe that there
would be good correlation most of the time.

Errors in caused by the frequency difference would be
minimized if G3AQC could transmit closer to HBG.
I am ignorant of both the law and QRM sources on this
band.  An old page on the RSGB site says 71.6 to 74.4 kHz.
Is it currently legal (and advisable) to Tx near 74.4?

The big unknown is how much error is caused by location
difference.  There seems to be pretty good amplitude
correlation between HBG and AQC as received by Dex,
so I am guessing that the delay correlation would be
adequate.  My apologies if this is way wrong.

73,

Stewart KK7KA

----- Original Message ----- 
From: "James Moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, December 17, 2002 3:20 PM
Subject: Re: LF: Re: QSO format


> Dear Stewart, LF Group,
> 
> At 19:48 16/12/2002 +0100, you wrote:
> >However, I believe that HBG 75 could serve as a "pilot" carrier.
> 
> In order to serve as a pilot carrier in this way, the signal from HBG would 
> have to be subject to exactly the same propagation effects and noise levels 
> as G3AQC - but since these two stations are operating in different 
> locations, on different frequencies, is it likely that this is actually the 
> case?
> 
> Cheers, Jim Moritz
> 73 de M0BMU