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Re: [TowerTalk] Ground wire impedance

To: K4SAV <RadioIR@charter.net>, towertalk@contesting.com
Subject: Re: [TowerTalk] Ground wire impedance
From: Jim Lux <jimlux@earthlink.net>
Date: Wed, 12 Jul 2006 18:10:53 -0700
List-post: <mailto:towertalk@contesting.com>
At 05:42 PM 7/12/2006, K4SAV wrote:
>  > Strap width   Inductance uH
>  >  0.5 in          0.40
>  >  1 in            0.36
>
>
>Given that a 0.5 inch wide strap is about the same as a wire.. what
>about multiple wires in parallel.. If they are spaced apart far enough,
>the inductances will be parallel.
>
>--------------------------
>
>Good thought, but this might be hard to implement at the bonding point
>if you are thinking of a ground rod/radial system. If you space two #4
>wires 6 inches apart you can get 0.72 times the inductance of a single
>wire.  If you space the wires 3.3 ft apart you can get 0.6 times the
>inductance of a single wire.


Hmm.. but, if I had four AWG 10 wires laying side by side, that's like a 
0.4 inch wide by 0.1 inch high strap... i.e. the L should be 0.40 uH (give 
or take) for the 10 foot run.  I suspect that 4 AWG16 (roughly 0.05" 
diameter) wires spanning half an inch would have about the same inductance, 
and 4 AWG16s is a lot cheaper than a single AWG4, or, perhaps, an 0.05x0.5" 
strip.  As you show in your table, (and you mention above) you have to 
spread over a MUCH wider distance to materially reduce the L.

Where I'm going with this is that there might be some very convenient, and 
inexpensive, ways to get a fairly low inductance connection comparable to 
AWG4, and potentially easier to handle.  For instance, there's AWG16 ribbon 
cable that shows up surplus every once in a while.  Or, perhaps, if there's 
a "deal" on cheap extension cords.  If DC resistance isn't the issue, you 
don't really need the copper mass of a big solid chunk.  Something with 
fairly small copper strands separated by plastic, paper, other fillers, can 
have an impedance for RF and/or lightning that's pretty acceptable.  Think 
of it as quasi Litz wire.


>Interesting link on "quarter shrinking".

Yes.. it's a fascinating process.  I imagine one could use it to crimp 
connectors onto ground rods, with great expense and complexity (and massive 
overkill.. like fishing with a "DuPont lure"). Certainly one can smoothly 
crush 3/4" copper pipe to about 1/4" OD.


>Jerry, K4SAV


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