Here's a method I used to assess the ground conductivity at the salt lake
bed where I have operated in a number of 160m contests.
The first time I raised the antenna there (a 1/4-wave balloon-supported
vertical) with four 125-foot radials, I used an Autek VA-1 meter to
measure the R + jX at the feedpoint. The reason I did this was to see if
only four radials would be enough over that moist, pure salt ground. I
was delighted to see that the feedpoint was 38 + j0 at resonance, which
meant to me that there was only about 2 ohms of ground loss with only
four 1/4-wave radials, given that the feedpoint Z of a 1/4-wave vertical
is about 36 ohms. Based on that, I decided that more radials were not
necessary.
Based on the table in ON4UN's book that shows the equivalent resistances
of various radial systems over "good" ground, the site's ground
resistance obviously is condiserably better, in fact -- better than sea
water!
Perhaps this method of estimating gtound resistance can be expanded upon
by some enterprising ham with more sophisticated measurement equipment.
I think such tests could be done on, say, 20 meters where the antenna
would not have to be so huge.
It would be nice if the next issue of John's book would contain a table
that showed the equivalent ground resistance for various radial systems
over all types of ground, from "very poor" to "very good" or better. It
would be very handy information for all Topbanders.
73, de Earl, K6SE
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