I received several inquiries off-list, so I'll summarize some of the answers
here, instead of replying individually:
No, you can't just multiply the inductance of one foot of wire by ten to
find the inductance of 10'. Use the calculator.
The inductance of both round and strip conductors increase as they approach
a ground plane or other conductors. So the free space inductance given by
the calculator link is lower than it would be in a typical installation.
It should scale similar to the strip calculator shows (compare a 120" long
conductor spaced 120" above the ground plane to only 12" above the ground
plane to get a ballpark idea of how a round conductor would vary).
Based upon actual rough measurements in my workshop, 10' of the following
conductors spaced about 12" above a concrete floor have the following
impedance at 10 MHz:
#6 copper wire = 330 ohms
0.5 copper pipe = 270 ohms
1.5" copper strip = 105 ohms
The impedance scales fairly directly with frequency (so the Z at 1 MHz is
10% of the above). The impedance varies significantly with different types
of "ground planes".
No, it isn't better to run the ground bus higher above ground just to lower
its impedance. I don't know why. But you always want your ground bus close
to ground, short and straight. Every sharp bend significantly increases the
inductance.
Steve, W3AHL
----- Original Message -----
From: "Steve W3AHL" <w3ahl@att.net>
To: <n4zr@contesting.com>; "TowerTalk" <towertalk@contesting.com>
Sent: Tuesday, August 18, 2009 9:29 AM
Subject: Re: [TowerTalk] inductance of tubing vs bar or strip
> Try
> http://www.k7mem.150m.com/Electronic_Notebook/inductors/wire_strip.html
>
> For a strip not over a ground plane, just set the height/thickness to some
> large distance (like 36 inches).
>
> Select the Inductor menu on the left to calculate round wire inductance.
>
> As an example a 12" long 1.5" wide strip has an inductance of about 0.046
> uH. A 1" round conductor (about the same surface area as the strip) is
> 0.148 uH (about 3x the strip).
>
> Steve, W3AHL
>
>
> ----- Original Message -----
> From: "Pete Smith N4ZR" <n4zr@contesting.com>
> To: "TowerTalk" <towertalk@contesting.com>
> Sent: Tuesday, August 18, 2009 8:16 AM
> Subject: [TowerTalk] inductance of tubing vs bar or strip
>
>
>> Can anyone suggest where I can find a calculator for the inductance per
>> foot of copper tubing compared to the same length of copper bar or
>> strip? I'm looking to understand the potential utility of using
>> soldered copper tubing for a ground bus, as compared to copper
>> strip/strap.
>>
>> --
>> 73, Pete N4ZR
>> New Articles Daily - the Contesting Compendium at
>> http://wiki.contesting.com
>> The World Contest Station Database, updated daily at
>> www.conteststations.com
>> The Reverse Beacon Network at http://reversebeacon.net
>>
>> _______________________________________________
>>
>>
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