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Message-ID: <3.0.1.16.19991124182607.3b47ad4c@mail.cc.kuleuven.ac.be>
Date: Wed, 24 Nov 1999 18:26:07
To: rsgb_lf_group@BLACKSHEEP.ORG
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: Radiation Resistance of Transmitting loops
In-reply-to: <943458240.26233.276@excite.com>
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The formula for a single-turn loop I found in the 'Taschenbuch der
Hochfrequenztechnik' is the same as Dave's.

73, Rik  ON7YD

At 07:44 24/11/99 PST, you wrote:
>Hi Dave,
>
>I've been reading your Home Page and came across a formula for the radiation
>resistance of a loop antenna:
>
>Rrad = 320*Pi^4*A^2/L^4
>
>where A is the area of the loop in square metres and L is the wavelength in
>metres.
>
>There is a similar formula in the LF Experimenter's Source Book, in an
>article on LF Transmitting Loops (page 2.25). No author is given, but it is
>attributed to "Break In" 
>July 1995. The formula given there (page 2.26) is:
>
>Rr = 7.72E-30*f^4*A^2*n^2
>
>where f is the frequency in Herz,
>A is the loop area in square metres,
>and n is the number of turns.
>
>Putting n = 1 as in your case and this reduces to:
>
>Rr = 7.72E-30*f^4*A^2
>
>The problem is that this formula gives results twice as big as your formula.
>A factor of 2 appears to have got lost somewhere in one of the two
>formulae.
>
>My question is, which one is right? If the second one is right, your loop is
>twice as good as you thought it was!
>
>One more question. Where can I get 3C85 ferrite rings? I've been through all
>the catalogues with no success.
>
>I hope to be on the air before too much longer. I put up a G5RV a few weeks
>ago for HF. Because the garden is short, the last 20 feet or so of each arm
>are turned down to about 8 foot above ground. Having tried a few calls it
>seems to be working quite well on HF. So now I have provisionally connected
>the two ends with a good thick multistranded earth type wire and supported
>it about 2 feet above the ground from one end to the other. The garden is on
>rather a dramatic slope, rising by over 20 feet at the bottom, so climbing
>boots were necessary.
>
>Like Steve ALG, I quickly found that a 300 ohm conventional feeder has got
>far too much resistance, so I must change that before I do much more, but I
>don't want too much weight on the antenna. The total DC resistance was found
>to be 1.8 ohms and after a few measurements and calculations I found that
>this is made up of:
>
>34 feet of 300 ohm ribbon		0.7 ohm
>15 metres of RG58CU		0.63 ohm
>102 feet of 16swg antenna wire	0.3 ohm
>lower loop wire			0.17 ohm 
>
>So the main thing is to replace the feeder and the coax. I don't fancy
>replacing the 16swg with 14swg, so I may have to live with that, but I may
>go for even thicker wire for the lower part of the loop. I've got some very
>heavy gauge 50 ohm coax with a 2.5 mm core, so this may do to connect the
>bottom of the feeder to the shack, using a balun/matching unit at that
>point.
>
>A loop of this type is attractive for me, because I can't really put up two
>antennas, one for LF and another for HF. Obviously for HF the lower part of
>the loop must be disconnected, but that doesn't seem too big a problem.
>
>73s 
>
>John, G4CNN, Locator: IO91ML
>
>
>
>
>
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