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Date: Mon, 21 Jul 2008 14:41:14 +0200
From: Rik Strobbe <Rik.Strobbe@fys.kuleuven.be>
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Quoting Andy Talbot <andy.g4jnt@googlemail.com>:

> 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 =3D 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
>

Another 2 cent (or 2 penny):
I just simulated the antenna as described by Andy with Mmana_gal:
- The radiation pattern is (almost) omnidirectional.
- The radiation resistance doubles compared to a single loop. But as =20
you use the double amount of wire (=3D double losses) efficiency will be =20
about the same I guess.

73, Rik  ON7YD - OR7T
  and compred it to a single loop



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