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Re: LF: Loop Conundrum

To: [email protected]
Subject: Re: LF: Loop Conundrum
From: Marco IK1ODO -2 <[email protected]>
Date: Mon, 21 Jul 2008 14:07:53 +0200
In-reply-to: <[email protected] m>
References: <[email protected]>
Reply-to: [email protected]
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At 13.29 21/07/2008, you wrote:
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?
Andy,

just my 2 cents: you have two magnetic fields in phase, that sum as vectors.
So, from a distance you see only one vector, sum of the two, with nulls and so on; and you sum the areas of the two loops, projected on the plane orthogonal to the vector. If the loops are orthogonal between them you have a 1.41 times the effective area, and two times the resistance. The radiation pattern is not omnidirectional at all, and the total efficiency decreases.
This is an intuitive reasoning... not scientific, HI.

73 - Marco IK1ODO / AI4YF



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