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[TowerTalk] Soil Conductivity -- UofH Clarification

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Subject: [TowerTalk] Soil Conductivity -- UofH Clarification
From: (Jim Reid)
Date: Fri, 27 Feb 1998 11:52:39 -1000
Aloha,  Well Hawaiian soil really isn't better at all!  In fact
it may be worse.  I just now have to understand the
following which just arrived from the Oracle of
Tropical Ag and Soils,  University of Hawaii:

"Soil conductivity is tricky to measure and lots of methods are
used.  In Hawaii we  make a paste of soil with 5 parts water and
one part soil by weight.  Other places use different "dilutions".
Also units are tricky.  

Decisiemens per meter are the same as millisiemens per cm and
a new standard.

Bottom line:

Let us compare Kauai uplands to the wheat growing plains of Kansas:

Kauai conductivity much lower.  Soil mostly oxide based, which
is very inert.  Ground water soft.

Kansas conductivity much higher.  Soil full of calcium based
clays which are easily solvated with acid rain (carbonates).
Ground water often hard as nails (loaded with dissolved
minerals). [ARRL Antenna Book shows most of  Kansas to be
in the 30 mS/m area;  best on the US mainland for antenna's
reflection performance!] 

So it is a measurement technique/units artifact.

So our volcanic soils have lower conductivity than
typical mainland soils for the reasons stated above.

Readings given are correct for Kauai soils in the decisiemen
per meter range using a paste of soil in water.  California
uses a different method of preparing the samples, for instance.
Kauai decisiemen per meter measurements are:

On  agricultural land such as pasture, one can expect
a soil conductivity (saturated with rain) of about 2 deci-seimens
per meter.

Undisturbed rain forest floor should be lower, due to lower chemical
content, more on the order of 1 deci-seimen per meter.

Typical Hawaiian  lawn  and garden may be as much as 4 deci-
seimens per meter, but typical is more like 3 deci-seimens per meter.

Soil in Kansas much more fertile, much more available nutrients,
much higher soil conductivity as a result.  Not based on inert
oxides as the weathered volcanic glass of Hawaii soils are.
True there are clays in Hawaii, as defined by particle size,
but they are also fine oxides and not fine calcium carbonates
from weathered sedimentary rocks as the clays in Kansas would
be.  Thus soil in Hawaii could care less about rain, acid or otherwise,
with or without carbon dioxide to increase the pH, they are
non-reactive, unlike the clay minerals in Kansas soils which
readily get solvated by the usual carbon dioxide in water
type acidity of normal rain.

 Check drinking water.  Oklahoma, hard as rocks.
Hawaii, usually nice and soft naturally.  Soil conductivity
has to follow the same pattern as ground water."

So seems as if most of what I posted yesterday about the wonderful
characteristics of Hawaiian soil for antennas was BS!!  However,  I am
not too sure about what I know today either.  I believe what he is
saying is that Kauai's soil  conductivity is 1 to 4 mS/m,  while in Kansas,
Nebraska and parts of Texas, it is 30 mS/m;  so we are only 1/10 as good
as there,  not 10x's better as believed yesterday!  Sounds as if we are
quite similar to the Atlanta area (per Dave Thompson yesterday) and
much of the SE and NE US mainland (and Nevada). 

To have verticals perform as well as at 6Y4A,  I now wish I
lived a bit closer to the ocean;  am now about  2  miles in and up
about 480 above the ocean.  A very gradual slope, interrupted by
water runoff wash ravines along the way,  including one deep 
one (maybe 50   or 60 feet deep and 600 feet wide)  right behind my QTH,
full of trees and rain forest foliage.

My verticals will be set up on the near side of this ravine wash just
down from the crest several feet.  The antenna's view closest to the
ocean will be due South,  with a nearly uninterrupted horizon
sweep the East to the West,  or around 180 degrees view
of ocean span.  North lies almost exactly diametrically across the
island some 23 miles to the North shore of Kauai.  MT. Waialeale
rising some 5100 feet,  is directly in line with due North and about
11 miles from here.

Well,  this is now long,  but I wanted to set straight the record on
Hawaiian soils.  Sorry for my over enthusiasm yesterday!

73,  Jim, KH7M

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