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Date: 21 Jul 2008 11:54 GMT
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Subject: Re: LF: Loop Conundrum
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Dear Andy,

I guess these two loops should be fed by two rf signals of 90 degrees
phase difference to become really omnidirectional. The same is true in
receiving. The two signals from the loops have to be combined by a 90
degrees phase shift network.

HW?

73 Ha-Jo, DJ1ZB


"Andy Talbot" <andy.g4jnt@googlemail.com> schrieb:
> 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.
> 
>