[TowerTalk] w7ekb & ground rods
marsh at ka5m.net
Mon Jan 19 16:58:46 EST 2015
I've just got to ask - who were the "experts" who said adding two (2) more
"radios" (sic) would help?
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Brian
Sent: Monday, January 19, 2015 3:54 PM
To: Jim Lux
Cc: towertalk at contesting.com
Subject: Re: [TowerTalk] w7ekb & ground rods
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 at 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)
> 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
> 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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