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Re: LF: RE: Loop Conundrum

To: [email protected]
Subject: Re: LF: RE: Loop Conundrum
From: "Mitch Buchman" <[email protected]>
Date: Mon, 21 Jul 2008 11:34:33 -0400
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How is this different from an eggbeater or turnstile antenna, that is
often used at VHF?

http://pagesperso-orange.fr/on6wg/Doc/Antenne%20Eggbeater-Engl-Part1-Full.pdf

and
ARRL Radio Amateur Satellite Handbook 1st ed, p10-16

Mitch
KB3MYC

On Mon, Jul 21, 2008 at 8:02 AM, Gary - G4WGT <[email protected]> wrote:
> Andy, LF,
>
> You wrote :-
>
> "Now, I take two identical such loops and mount then on the same centre line
> but at right angles to each other so there should be no coupling
> between them, whatsoever.   Now, I connect the two loops in series and
> resonate the combination with a single capacitor of half the original
> value."
>
> I have been pondering about something similar as I have problems remotely
> rotating yet another antenna.
>
> My idea is to make the loops in the same way as you describe but feed the 2
> loops to the two inputs of a balanced pre-amp like the G3LNP loop pre-amp
> shown in the "LF Experimenters Handbook"
>
> What are your thoughts on that please.
>
> Gary - G4WGT.
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of Andy Talbot
> Sent: 21 July 2008 12:30
> To: [email protected]
> Subject: LF: Loop Conundrum
>
> Was pondering this while out walking the other day, and couldn't come
> to a satisfactory conclusion either way...
>
> A small magnetic loop mounted vertically has a defined radiation
> resistance that is a function of its diameter, a loss that is function
> of its conductor and hence a loss or efficiency that is the ratio of
> the two. It is resonated with a good quality vacuum capacitor, and
> fed/matched by any suitable metrhod.  Lets also leave aside all the
> myth and folklore about small loops, and also ignore the environment
> for now.   It also as a radiation pattern with nulls.
>
> Now, I take two identical such loops and mount then on the same centre
> line but at right angles to eachother so there should be no coupling
> between them, whatsoever.   Now, I connect the two loops in series and
> resonate the combination with a single capacitor of half the original
> value.   The resulting radiation pattern should have the nulls filled
> in, and be a reasonable approximation to omnidirectional in azimuth.
>
> BUT...
> What is the resulting change in efficiency?
>
> Argument 1:
> Two identical loops = two times the loss R,  but also two times the
> radiation resistance (since they don't couple) so net efficiency
> remains the same.
>
> Argument 2 :
> Chu-Harrington relates efficiency / Q / bandwidth / volume enclosed.
> Therefore, as the enclosed volume has increased, the effciency ought
> to rise.
>
> Both arguments developed little side trendrils & thoughts as I walked
> and pondered, and both appear valid in their own way.  So
> the floor is open for discussion :-
>
> And where does the net radiation pattern fit into the equation?  Does
> it, at all ?
> --
> Andy G4JNT
> www.scrbg.org/g4jnt
>
> ps.  Fascinating paper on EMP btw. - I was up way past midnight last
> night  reading it.
>
>
>


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