"Richard Clark" wrote in message
...
On Fri, 20 Apr 2007 07:58:16 +0100, "Richard"
wrote:

More like the radials make the ground below your feet more like say
a pool of salt water than the high resistivity ground that it normally is.
What do you think?

Hi Richard,

Actually salt water sucks as a local ground - it is as poor a "good"
conductor as you could imagine. Carbon is a far better conductor than
salt water, but no one yet has suggested building on top of a coal
seam.

You would be better off filling your yard with sand to the depth of 30
feet or so (yeah, sure). The testimonials attributed to salt water
comes with its far field qualities of a tremendous mismatch to air and
offering spectacularly low radiation launch angles.

So, copper replaces a very poor conductor (as a first pass
approximation). Invest your copper in close proximity to the base of
the antenna. That is, a lot of short radials, and a fair number of
medium size ones, and a few long ones.

Two things to consider. The ground closest to the antenna is
responsible for efficiency in loading. The ground further out
(between 5 and 10 wavelengths, or more) is responsible for launch
efficiency (offering lower launch angles).

Hmm, a new concept introduced.

I was thinking on these lines.

The first thing to do is to prepare the ground, that is, alter the nature of
the ground in the vicinity of the antenna from an electrical point of view.
To improve from "poor ground" to "good ground", in an electrical sense. That
can be done by laying wires in the ground (radials) or a wire mesh. Once
that is done, one is in a better postion to have the best RF ground
possible. I think this is what the radial/wires do, they simply alter the
nature of the ground where they are placed. This is like making poor ground,
good ground or good ground, excellent ground by laying wires in the ground.

Now what seems to be the case is that there is an advantage in making the
ground nearest the antenna the very best ground that you can. So, if you are
going to use wires to better the ground, make sure that most radials go in
near the base of the antenna.

Of course, wires improve the ground, it's conductivity, but in practice, you
tend to connect the antenna to the radials/wires rather than make for
seperate arrangements.

On Fri, 20 Apr 2007 09:02:34 +0100, "Richard"
wrote:

The first thing to do is to prepare the ground, that is, alter the nature of
the ground in the vicinity of the antenna from an electrical point of view.
To improve from "poor ground" to "good ground", in an electrical sense. That
can be done by laying wires in the ground (radials) or a wire mesh. Once
that is done, one is in a better postion to have the best RF ground
possible. I think this is what the radial/wires do, they simply alter the
nature of the ground where they are placed. This is like making poor ground,
good ground or good ground, excellent ground by laying wires in the ground.

Hi Richard,

Yes, this is a good analogy. It fails quickly, however. That is, you
do not gain better ground characteristics in proportion to the number
of radials.

So, as general rules go, the common advice is to make your radials as
long as the radiator is high, and to lay out as many as you feel
comfortable doing. If you need a hard number, then a dozen to sixteen
is a good starting place from which others can argue ceaselessly to
offer you to gain only 1 more dB of performance (maybe 2).

Now what seems to be the case is that there is an advantage in making the
ground nearest the antenna the very best ground that you can. So, if you are
going to use wires to better the ground, make sure that most radials go in
near the base of the antenna.

Of course, wires improve the ground, it's conductivity, but in practice, you
tend to connect the antenna to the radials/wires rather than make for
seperate arrangements.

True, that is the sense of a counterpoise. However, even a ground
field beneath a dipole overhead improves the dipole's performance and
there is no direct connection there. Some would argue this only
describes a yagi pointing straight up and the gain only comes to more
power poured into the clouds. Yes, this is an appealing argument, and
yet if you consider how much the gain rises at a low angle of launch;
then you find it is beneficial in that respect as well.

The alternative view of radials is that they operate as a shield
against loss.

73's
Richard Clark, KB7QHC