[TowerTalk] [Bulk] Re: [Bulk] Re: copper or galvanized ground rods in red SC clay

[Roger D Johnson]

On 1/9/2016 9:38 PM, Grant Saviers wrote:
> Roger,
>
> Do you propose that it is not necessary to achieve the recommended 5 to 10 
> ohms of resistance in a tower ground system?

Recommended by who and for what purpose?

> What is your measurement technique to determine if the actual construction is 
> likely to be effective?

There is no measurement technique that I know of. Just use good RF design.
>
> Grant KZ1W

There are factors in the design of a lightning ground system that are not 
relevant in a power line safety
ground. generally speaking, a safety ground is not usually a good RF ground but 
a good RF ground is
usually a good safety ground.

Another factor not usually considered by hams is that conduction through the 
ground is NOT the same
as conduction through a copper wire! A copper wire has a copious supply of free 
electrons and will
happily conduct increasing amounts of current until it melts. In soil, the 
conduction is by ions from
metallic salts in the earth. The supply of ions is finite and when all are being 
used to conduct electric
charges, the resistance rises sharply. The soil has gone into "saturation". A 
lightning ground system
has to be designed to dump the current from a strike into a large "volume" of 
earth capable of conducting
the strike current.

We've all seen the illustration in ARRL Handbooks that show the doping of ground 
rods with rock salt or
Epsom Salts. This is to increase the number of ions available for conduction.  
Different soils have different
amounts of minerals, each case is individual. Water content also affects 
conductivity as does temperature.

To sum it up...there is no "one size fits all" solution.

73, Roger

>
>
>