From: Jim Brown
> On 10/3/2012 12:35 AM, Bob Kupps wrote:
> > "It is impossible to make a direct measurement of ground characteristics".
> Horsepucky. Now, what IS difficult is to make a direct measurement to
> great depth! But N6LF has shown a simple method to measure to the depth
> of whatever length of rod you are willing (and able) to drive.
My 2 kopeikies:
Ground characteristics vary from antenna base out, and down. We hardly know
what is in the ground, could be clay, sand, rock, water, ????
It really boils down to two extremes:
1. Salt water vicinity
2. Everything else.
We are trying to achieve that "perfect" RF ground either by moving to 1. or
making 2. look like 1. by using radial or screen fields as large as possible.
We can see 1. as a close approximation of "RF mirror" with low losses and good
participation in pattern forming.
We can see 2. as "thick RF sponge mirror" with variation of characteristics
depending on ground composition down to ???
As VE3BMV I was stuck with Big Bertha on a small city lot back in Toronto
suburb. Good clay, but I would try to imrove the "mirroring" by watering the
heck out of the tower base with sprinklers before the contest and liberal
amount of fertilizer. I noticed that reception would get more quiet (background
noise) and I would be getting out better. I noticed those changes after heavy
rains, so here comes my own "rain" when needed.
The point is that by watering the ground in the vicinity of antenna, we help it
to look more like mirror, rather than RF sucking sponge. MInerals in the ground
and water improve surface conductivity - mirroring.
Academic discussion about ground conductivity and how to measure it is
interesting, but for ham stuck in a city or his QTH does little to do much
about it. If one is looking for QTH in low lands, look for clay, wet lands,
high water table, or ultimate - salt water beach. Knowing your own conductivity
is interesting to predict antenna pattern, but normally you can't do much
except watering it, making it more like mirror on the surface, rather than
thick sponge. Looking for high water table is the best one can do inland.
Best vertical inland so far I have seen is at W8LRL - lonely 3/8 radiator 200'
tall, with 360 radials 200' long on a small hill. Excellent low angle
performance in pastoral fields and no RF sucking structures around.
Wanna eye opener? Drive mobile around shore and observe signal levels from
water edge to inland. I did that at Cape Hatteras, NC and "verified" Team
Vertical findings from 6Y5.
Oh, I have my 1972 Buick LeSabre radiomobile for sale, with or without rigs
160m - 70cm (800W) - large capacitive coupling to ground.
Yuri, K3BU.us
www.MVmanor.com
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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