Envelope-to: dave@picks.force9.co.uk
Delivery-date: Thu, 21 Jul 2005 16:02:06 +0100
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From: "Stewart Nelson" <sn@scgroup.com>
To: rsgb_lf_group@blacksheep.org
References: <000001c58dee$2f258c90$e6a4c593@RD40002>
Date: Thu, 21 Jul 2005 08:02:02 -0700
Organization: SC Group
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Subject: Re: LF: Combatting Loran
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Hi John and all,

Is the cave TX using a loop (wire or earth)?

If so, I would expect the cave signal to be mostly
magnetic, so an electric LORAN antenna, e.g. 1 m whip,
would pick up little cave signal, even if it is in
the vicinity.  I would guess that since you are in the
middle of nowhere, other noise should not be a problem,
unless it's from your own gear!  However, it may take some
work to achieve good cancellation over the required bandwidth.

Regards,

Stewart KK7KA

----- Original Message ----- 
From: "james moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Thursday, July 21, 2005 5:17 AM
Subject: RE: LF: Combatting Loran


> Jim,

>Do you think this approach would be worth trying at the surface station of a
> cave radio link?

> Regards,
> John G3PAI

Dear John, LF Group,

What you need to make this kind of scheme work is two antennas which have
different relative amplitudes and/or phases of the wanted and unwanted
signals. This allows you to adjust the amplitude and phase of one antenna
output to cancel the unwanted signal from the other, but without at the same
time cancelling the wanted signal. If you can arrange an auxiliary receiving
antenna that picks up the Loran noise without picking up much of the cave
radio signal, the system should work. I imagine this would be fairly easy
due to the "near field" nature of the cave radio signal - just putting the
auxiliary antenna further away from the cave radio TX should do the trick.
Note that other noise sources present at either antenna generally will add
rather than cancel in the combined output, so it is important that the
additional antenna has a good SNR (or Loran noise/Other noise Ratio might be
a better way of putting it) if you expect to improve the overall SNR.

Cheers, Jim Moritz
73 de M0BMU