[TowerTalk] Verticals and well pipe grounding

[jimlux]

On 2/6/16 9:47 PM, Jim Brown wrote:
> On Sat,2/6/2016 4:22 PM, jimlux wrote:
>> Using N6LF's formulas I get skin depths around 5-10 meters at 2MHz
>> (0.005 S/m, epsilonr = 3-10)
>>
>> You might get 60 feet (20 meters) if the soil is particularly
>> non-conductive (rock).  Dropping the conductivity to 0.5 mS/m gives
>> you skin depths of 22-34 m at 2MHz
>
> Rock and sand are quite prevelant throughout the west, and pretty much
> what we have in the mountains. :)
>

yes, but..  It's a pretty rare ham shack that sits on a granite outcropping.

And most rock is actually ok from a conductivity standpoint.

http://emgeo.sdsu.edu/emrockprop.html

sedimentary rocks like shales have pretty high conductvity (100 mS/m). 
To get down to 0.5, you're looking dolomite, limestone.
The usual granitic sort of stuff also seems to be reasonably conductive, 
unless you're looking at shield, unweathered rock.

There's also a frequency dependence.. so looking up a table for low 
frequencies (line frequency, etc) might not be a good baseline.


> 73, Jim K9YC
>
>
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