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Message-ID: <5.1.0.14.0.20020402162043.00a96d80@gemini.herts.ac.uk>
Date: Tue, 02 Apr 2002 17:08:54 +0100
To: rsgb_lf_group@blacksheep.org
From: "James Moritz" <j.r.moritz@herts.ac.uk>
Subject: Re: LF: loop inductance
In-reply-to: <3.0.1.16.20020402140550.30cf29da@pb623250.kuleuven.be>
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Dear LF group,

In Rik's formulae, if you make W in m equal d in mm, the formulae reduce to 
L=1.1W, give or take a few percent,depending on shape - close to RA9MB's 
formula L=W for a single turn. I have not tried a big TX loop, but the 2m 
side square loops made of 15mm diameter tube I have been using lately have 
L=7.9uH, very close to Rik's square loop formula and Yuri's simple formula; 
a 1m square loop of the same tube had L about 4uH. Making the wire thinner 
increases L, but is not very critical because of the Log component. A 1m 
square loop of about 1mm wire had L of about 6.4uH, which agrees with Rik's 
formula which predicts 6.1uH.

Alex's formula L=WN^2 makes the inductance proportional to N^2 for a 
multi-turn loop; in practice the inductance will always be somewhat less 
because there is not unity coupling factor between the turns. A 10 turn, 
1m^2 loop made using 1mm PVC insulated wire in a bundle had an L of about 
340uH rather than 400uH The error will depend on the spacing of the turns 
and how they are bundled together and so on. All the same, it seems like a 
good way of making a rough estimate - in practice, there will be many 
factors that have a slight effect on the actual value of L, so a rough 
estimate is probably all that is required.

Cheers, Jim Moritz
73 de M0BMU