On Mon, 31 May 2010 00:33:00 -0400, Fred McKenzie
wrote:

I have a steel well pipe that is approximately a quarter wave on 40
Meters. Even though it is buried, why wouldn't this work as the bottom
half of a vertical dipole?

Hi Fred,

One perspective of the radial field is that it shields the radiator
from the loss of ground. However, that simplification disguises the
fact that the radials radiate too - and unproductively. When every
radial's radiation is taken into consideration, opposite radials (each
one that is 180 degrees from the other) cancel.

That aside, their benefit is they conduct better than dirt. What this
means is more power goes into copper/steel instead.

Now, if we consider your well pipe, it goes deeper into that lossy
dirt and the deeper it goes, the more dirt the return signal (to the
other, the vertical radiator) has to go through. More loss than use.

OK, another reason. For as poor/well as dirt may conduct, it too has
skin effect. This means at some distance into the dirt, conductivity
plummets because of skin effect. Deeper yet, and the skin effect loss
increases at a quick clip.

As skin effect is frequency dependent, at really low frequencies, your
well pipe has some advantage. This frequency range is suitable for
working lightning whose top end is 1MHz. At 7 MHz, there's no point.

I tried it with a mobile whip as the vertical element. It worked better
than I expected, but not really well.

Which shows you how crummy the whip is because what well pipe there
was that was above ground was doing the job of the whip.

Step back and look at the big picture using your analogy of a vertical
dipole with half of it buried. Now, convert that buried half into
multistrand. Bend each strand 90 degrees so that each strand just
rides an inch or two above ground with all of the newly bent strands
in a flat circular spray around the upper half. Walla! as the French
say.

73's
Richard Clark, KB7QHC