[TowerTalk] Verticals and well pipe grounding

[Jim Brown]

An FCC map of ground conductivity in the lower 48 can be downloaded at 
this link.

https://www.fcc.gov/media/radio/m3-ground-conductivity-map

On this page is a link to a 6.8 MB zip file which contains a grid of 
8.5-in x 14-in pages that are sections of the full map.  The contours 
are fairly rough, with a factor of 2:1. This map is fairly old -- it 
seems quite close to the one I worked with in Pete Johnson's consulting 
office in 1961. My guess is that it does not show the poorer ground 
conductivity of developed population centers described in the soil 
characteristics for NEC.

N6LF shows a procedure for measuring soil characteristics on his 
website, and it's been one of those things that W6GJB and have had on 
our list of things to do for several years.

73, Jim K9YC

On Sun,2/7/2016 5:16 AM, jimlux wrote:
> 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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