----- Original Message -----
From: "Peter Sundberg" <sm2cew@telia.com>
To: "Tom Rauch" <w8ji@contesting.com>
Cc: <towertalk@contesting.com>
Sent: Saturday, October 23, 2004 11:50 AM
Subject: Re: [TowerTalk] Ground radials/elevated radials
> Tom,
>
> What kind of A/B FS comparison could be done by disconnecting radials that
> already lay on the ground under the vertical, for example with a large
> relay??
>
> Say you have 50 radials spread out, and for the A/B test you disconnect 40
> of them connected to a bus wire via a relay, will this be equivalent to
> just having 10 radials under the vertical?
No, because the radials are still there, and interact with the field.
Interestingly, one of the validation cases for NEC-3 (which supports buried
structures) was whether a buried wire could be detected by it's effect on a
dipole in the air above it.
This is what makes testing so difficult. Even if you dig up the ground and
recompact it between test runs, it's unlikely to be that repeatable, unless
you make dozens of runs, which is somewhat expensive.
>
> If this is possible it would be a nice way to evaluate the performance of
a
> full radial system vs a light one, however I have a feeling it is not that
> easy..
>
> Any thoughts, has anyone tried this?
What you CAN do, in a modeling sense, is the following:
Pick some reasonable epsilon and sigma.
Model the light radial field.
Model the heavy radial field.
Compare the difference.
Pick some other reasonable epsilon and sigma
Compare the difference
repeat a dozen or so times.
With this data, you'll be able to tell if there is likely to be a
"significant" difference in performance between the radial fields. It won't
tell you what the performance of your antenna will be (because it's unlikely
that the ground model has sufficient fidelity), but it will tell you if it's
a 1% or a 10% kind of effect, or if something like soil properties changes
it more. Particularly if you're somewhere that has intermittent rain, so
the water content of the soil varies a lot, (which will change the epsilon),
the variations from soil moisture might dominate.
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