[TowerTalk] Short Ground Rods??

[Jim Lux]

At 10:06 AM 5/19/2005, K4SB wrote:
> >  That AZ soil sounds as bad as what I had in New England.  Good luck OM.
> > Dudley - WA1X
>
>Yep, and like that I have where my crank up is installed. Guy who dug
>the hole had to leave twice to get larger backhoes. First 2 would
>hardly scratch the surface.
>
>But, more to the point, would there be public surveys of soil
>composition ( or rock ) available? Like a government or AZ web site?
>
>73
>Ed


There are all sorts of geological and soil maps around, but they generally 
don't give the information you're really looking for, which is the soil's 
electromagnetic properties at HF on a fairly fine grid.

For instance, around where I live (Southern California), there are 
geological maps available that give the type of rock underlying the soil at 
a scale of 1:24,000 (that is, they match the standard topo maps).  That's 
great if you wonder what kind of bedrock is under your house, or if you're 
building an entire subdivision.

There are also soil distribution maps from the soils conservation service 
(a federal agency) and from the local agricultural extension.  However, 
they're at that same sort of scale, and merely tell me that I have loosely 
consolidated quaternary sediment with the potential for expansive 
clay.  They don't tell me things that have a huge bearing on EM properties, 
namely water content.

The maps are useful because being in an area identified as a expansive 
clay, or within an Alquist-Priolo Special Studies zone (near an identified 
earthquake fault), or in an area identified as prone to landslide or 
liquefaction, triggers additional requirements for some building permits 
(you might need a soils analysis for instance).


Easiest way to find out what the soil em properties are is to measure 
it.  Get a couple of metal rods to make a length of "open wire" line, drive 
them into the ground at the right spacing (1/2" rods 6" apart, I think), 
hook up a suitable transformer and fire up the MFJ antenna analyzer.
It's all in the ARRL Antenna book.