For what it's worth, I'll add my voice to Dave's and Danny's. The change
in velocity factor Danny speaks of is on the order of a factor of 5 for
ordinary soil. That is, a quarter wavelength under the ground is about
1/5 the physical length of a quarter wavelength in free space or well
above the ground. So if you did need to "tune" buried radials for any
reason, you'd have to make them about 1/20 of a free space quarter
wavelength. And the "tuning" would be extremely broad because of the loss.

To amplify what Dave said, the current on an elevated or free space
radial has nearly the same distribution as on a dipole half -- it's
maximum at the feedpoint and drops to zero at the end, following a
nearly sine shaped curve. When buried in the lossy ground, it instead
decays in a more-or-less exponential fashion. In some cases there are
some remnants of the free-space distribution, but they're very muted. So
basically, the current just fades out as you get farther and farther
from the feedpoint. At the point where the current has dropped to a low
value, you can cut the radial with no significant effect. This is very
much different from the behavior above ground.

I'm not surprised to find technically inaccurate material coming from
antenna manufacturers. Although they might know how to build antennas,
and certainly how to sell them, they often don't have any great depth of
knowledge of fundamental principles. (In fact, a lack of knowledge of
fundamental principles is often an advantage in the selling area,
because it gives them an excuse for making claims of impossible
performance, and the invention of non-existent phenomena to explain it.)
I recall many years ago contacting a major manufacturer of coaxial cable
about a theoretical matter, and found that they knew nothing at all
about how transmission lines worked. They were experts at extruding
polyethylene and PVC and at weaving fine copper wire, and nothing else.

Roy Lewallen, W7EL

Dan Richardson wrote:
On Fri, 7 Jan 2005 14:04:43 -0600, "Charlie"
wrote:


You're entitled to your opinion on this seemingly controversial topic.
73 / DX ..hope to catch you on the bands one day Dave


Possible the controversy is in your mind Charlie.

The velocity factor using wires buried under ground is a fraction of
the velocity factor in air or free space. Hence if you are hell bent
on having resonance in your buried radial system (which in this
application does nothing to improve system efficiency) they need be a
whole lot shorter than the length = 234/F that is used for elevated
radial systems.

Danny, K6MHE