Message-ID: <003701cb2667$39072e50$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <002401cb2662$106e5db0$0401a8c0@xphd97xgq27nyf> <06EC7774-839A-4E75-835C-717830FE5963@leeds.ac.uk>
Date: Sun, 18 Jul 2010 11:51:48 +0100
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Subject: Re: LF: EARTH MODE
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Chris
Receiving signals on a piece of wire lying on the ground is  totally
different to Transmitting a signal over any distance. You are getting into
the beverage antenna theory where signals can be received with some
advantage but useless for Transmitting, which is what some are trying to do.
Cave radio techniques are totally different where the requirement is to TX
for only several tens of metres.
Cave radio comparisons are only confusing the issue.
mal/g3kev

----- Original Message -----
From: "Chris Trayner" <C.Trayner@leeds.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, July 18, 2010 11:33 AM
Subject: Re: LF: EARTH MODE


Hi Mal,

Thanks for your comments.

On 2010 Jul 18, at 11:14, mal hamilton wrote:
> It would appear what some are using for antennas ie Earth Mode, I am using
as a ground system for my Airborne antennas.
> No wonder maximum tx range is very limited. A more straight forward
approach to cover the same distance would be a megaphone.

However, we need to bear in mind that running two wires out to tent pegs in
the ground does more than give you a double Earth connection. They can act
as effective aerials. For their use in cave radio the propagation mechanism
is still debated, but they can provide more than earth mode above ground.
When we were using them for cave radio in the West Riding some years ago, we
picked up Finbar from Malin Head on 73kHz. That wouldn't have been earth
mode. Also, one of the problems with cave radio on 87kHz is that it suffers
ACI from Loran, and the nearest Loran Txs are hundreds of km away.

73,
Chris G4OKW

-----------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032