Topband: ground characteristics

[k3bu at optimum.net]

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