910 micro Henry sounds like a very useful loading coil to me!! I have had no
difficulty using a ground rod as a counterpoise to my vertical. In fact it's
done extremely well. I added two radios because the experts said it would make
it work better. It didn't.
Best regards - Brian Carling
AF4K Crystals Co.
117 Sterling Pine St.
Sanford, FL 32773
Tel: +USA 321-262-5471
> On Jan 19, 2015, at 12:15 PM, Jim Lux <jimlux@earthlink.net> wrote:
>
>> On 1/19/15 8:45 AM, Ken wrote:
>> It seems to me that the ground above my rock layer (@ 36-40”) gets really
>> dry during the summer. Does that dry dirt have enough conductivity to be
>> useful? I do not know the answer to that question.
>>
>> Are there different answers depending on why we have the ground rod? (RF
>> ground, power line ground, or lightning protection)
>
> Yes..
>
> ground rods make terrible RF grounds, in general (where RF is HF and up):
> skin effect means that wires and rods have high ac resistance. (skin depth in
> copper at 10 MHz is about 0.8 mils/0.02 mm.)
>
> They also have significant series L (1 microhenry/meter for a wire.. so a 30
> foot run to the rod is a 10 uH inductor, that's 600 ohms reactive impedance.
>
> Rods are really for electrical safety ground and/or lightning ground. And
> they don't work all that well for that, unless deployed in large numbers.
> The advantage of a rod is that it's easy to install by driving, but as an
> electrical connection to the earth, it's just not that wonderful: the surface
> area is quite small (8 foot rod, 1" in diameter is only 300 square inches.
> You could probably do better, electrically, by burying a 1 foot square plate
> (288 square inches).
>
>
> Rods are also used in phone and power line applications.. you drive a rod at
> every pole (or wrap the ground wire around the foot of the pole when planting
> it). Even if any one rod has crummy characteristics, there's lots of other
> rods in the circuit to help establish the common voltage reference and
> provide a fault current return. I've had telco installers drive a new rod
> next to the existing rods on the general principle that at least they knew
> the new rod was in good condition: faster to just do a new rod than to test
> the existing one.
>
>
>
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