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Re: [TowerTalk] Fwd: Tower base/Ufer ground

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Fwd: Tower base/Ufer ground
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Sun, 18 May 2014 05:17:43 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 5/18/2014 12:44 AM, Jim Lux wrote:
On 5/17/14, 9:13 PM, Roger (K8RI) on TT wrote:
On 5/17/2014 11:27 PM, Jim Lux wrote:
On 5/17/14, 6:11 PM, Drax Felton wrote:
What is the conductance per inch of concrete in mho's ?


http://www.k1ttt.net/technote/concrete.html
10-50 mS/m

Shouldn't the medium be in cubic units?


No.. it works out right if you do the dimensional analysis..

Not if you do the math right.


Resistivity is in ohm-m, conductivity in 1/(ohm-m) or S/m (since S is 1/ohms)
Resistivity is not ohms per m, it's usually given as ohms per cubic centimeter.

Resistance usually is dimensionless, unless it's bulk and then it's so many ohms per unit length

You are confusing resistance with resistivity. You are losing a unit somewhere because resistivity is ohms per cubic meter or more often ohms per cubic centimeter. Look up the dictionary definition. Resistance is between two points. Resistivity takes into account the volume as the units are . Resistivity is in ohms per cubic centimeter. I worked with developing standards for liquids and circular solids With a Silicon production company for many years. The dictionary definition: for resistivity takes into account both area and length. IE: volume as in resistivity ohms ^3 cm. Had a devil of a time getting the techs to stop confusing the two. The easiest was to give them a probe consisting of 2, 1cm square plates, 1 cm apart, then thy had no conversions.



Resistance = Length * resistivity/cross sectional area.

No. Again that is resistivity

so to get ohms as resistance, you need resistivity to be ohms * length (because Length/area is 1/length)

Likewise, conductivity is = Area * conductivity/length, so it needs to be Siemens/meter



Conductivity is the reciprocal of resistivity, not resistance. Please stop working the formulas and just look up the definitions

73

Roger  (K8RI)




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