Envelope-to: dave@picks.force9.co.uk
Delivery-date: Thu, 21 Jul 2005 13:19:05 +0100
From: "james moritz" <j.r.moritz@herts.ac.uk>
To: rsgb_lf_group@blacksheep.org
Date: Thu, 21 Jul 2005 13:17:38 +0100
Message-ID: <000001c58dee$2f258c90$e6a4c593@RD40002>
MIME-Version: 1.0
Importance: Normal
In-Reply-To: <200507202019290658.0651F0B9@mail.zetnet.co.uk>
Subject: RE: LF: Combatting Loran
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org


-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of John Rabson
Sent: 20 July 2005 20:19
To: rsgb_lf_group@blacksheep.org
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