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From: "Ashlock,William" <William.Ashlock@edwards.boc.com>
To: rsgb_lf_group@blacksheep.org
Subject: RE: LF: TX Loop antenna conductors
Date: Mon, 18 Mar 2002 12:25:00 -0500
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Hi John,

I did a lot of reading about proximity effect in a number of old college
text books of mine
yesterday (who woulda thunk that this boring stuff would come in handy some
day?). The new
numbers I calculated are closer to yours than my 3/5.
  
>I find the usual formula for the ratio of Rac/Rdc = d*sqrt(mu*f/rho) very
unsatisfactory for
>small diameters, since as d gets smaller the ratio cannot get less than 1.
The same is true for >low values of frequency. Instead I use a couple of
series approximations to the Bessel
>functions. So I checked your figures and found for AWG #12 at 185kHz, a
ratio of 3.6 and for #8 >a ratio of >5.56, quite close but slightly higher
than your figures. 

>The point you made is of course why it is better to use properly made Litz
wire to keep the 
>advantage of thicker wire.

Right. I'm still pondering what the spacing should be between two #12 Litz
wires to keep the proximity effect to <10%. I'm calculating something like
0.12" but this is much closer than originally thought. Does your math handle
this?

Thanks,  
Bill A


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