|
Spring 2006 Issue |
|
|
Connecting Wires to
Rocks |
|
|
Have you ever tried to drive an 8-ft. ground into rocky soil—or into solid rock? Many of us have experienced the smarting pain as the hammer handle smacks the hands. Have you seen a ground rod go in for a while, only to make a 180-degree turn and reappear behind you? Maybe it was hilarious at the time, but it is hardly a useful electrical connection!
There is a solution to this problem, but one
that is not well known. One of us (J.J.) recently received a short paper
from Utah, wherein the authors used a bentonite slurry to encase a ground
rod, thus expanding the electrical diameter of the rod.1 References to
this article brought us to others, one American,2 the other Slavic.3 From
this review we learned of the superiority of this natural clay, which
contains the mineral montmorillonite, as an adjunct to grounding at sites
with poor soil conductivity.
A quick visit to the internet reveals hundreds
of references to this widely used material of volcanic origin. It is used
in the mining of oil, metal casting, pelletizing, grouting and sealing,
and as a base for cosmetics. Aluminum and silicon form the metallic
crystalline structure. With water added, ionization of the resident oxides
of sodium, potassium, and calcium occurs, forming an alkaline electrolyte.
Resistivity falls quite low— ~250 ohm-cm at 300% moisture—at which point
it swells up to 13 times its dry volume. This striking sponge-like
“hygroscopic” property makes the material unique. Unlike ground-enhancing
electrolyte solutions, there is no leaching out over time, and thus no
replenishment with pricey patented chemicals is required. The material is
non-corrosive. It is very sticky when wet and adheres tightly to any
adjacent surface.
We examined two west Texas radio sites, the
first located on a mesa near Ft. Stockton, the second on a low mountaintop
near Sanderson. Both sites have a solid-limestone rocky base. Ft. Stockton
has some sandy soil cover sufficient to support several species of cactus,
some junipers, and a little grass; the Sanderson site is bare rock. |
Photo 1. Mike, KD5FVZ, gouges the trench for the ground system. Note tower base and our tiny radio shack in the background. |
|
Click here to return to Spring 2006 highlights Click here to subscribe to VHF _________________ © Copyright 2006, CQ Communications, Inc. All rights reserved. This material may not be reproduced or republished, including posting to a website, in part or in whole, by any means, without the express written permission of the publisher, CQ Communications, Inc. Hyperlinks to this page are permitted.
|
|
