Message-ID: <387F8B6F.A985F270@netins.net>
Date: Fri, 14 Jan 2000 14:47:43 -0600
From: "Tom Gruis, Ed.D." <donnatom@netins.net>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: 35 km band
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100%.  I meant to be brainstorming more than advising.  Doc.

Rob Gill wrote:
> 
> At 12:25 14/01/00 -0600, Tom Gruis, Ed.D. wrote:
> 
> >You might also check out "cave radio" and spelunkers (Sp.?) pages.  I
> >have read articles in the past about these frequencies.  One thing that
> >comes quickly to mind is direct loop to loop transmission.
> 
> The problem with loop to loop operation at these frequencies is that is
> subject to the inverse cube law of magnetic induction rather than an
> inverse square law. A few hundred metres is a useful range for a cave radio
> but the power required for greater range very quickly becomes impractical.
> 
> The "earth bi-pole" approach of John Taylor G0AKN, referred to by Andre'
> Kesteloot a few days ago, may be a better approach at these frequencies
> (ref: the exchanges regarding the AMRAD Antenna about a week ago). This
> technique is now frequently used for cave radio purposes with significantly
> greater range when one or both of the inductive loop antennas is replaced
> with an "earth-current" antenna. Cave radios generally operate at 73kHz or
> above rather than audio frequencies.
> 
> I know that John has recently experimented with some success at audio
> frequencies, and I think he monitors this mail reflector. I'm sure he would
> be happy to offer advice on antennas for the 35km band.
> 
> Rob
> 
> +------------------------------------------------------------------------+
> Rob Gill, Cave Radio and Electronics Group
> 61 Cross Deep Gardens, Twickenham, Middlesex
> TW1 4QZ, England
> email: creg@bcra.org.uk
> +------------------------------------------------------------------------+