"Richard" wrote in message
...

I said:

Maybe a 3 foot wde cylinder would be adequate.

One thing: Why are radials so effective? They are not resonant
counterpoises, and from the aspect of surface area in contact with ground,
radials have hardly any surface area that "connects" with "the earth". I
can understand if I put in a 20 foot by 20 foot copper plate flat in the
earth that would "connect" to earth quite well, I mean the measured ohmic
resistance to "the earth" could be quite low. But also capacitive coupling
would be low too. But radials have no real capacitive coupling to "the
earth" neither much surface area in contact with "the earth". So it
confuses me as to why they are so effective.

BTW, since it looks like many wires in the earth are as good as a plate,
perhaps I could put in a wire mesh grid about 1 foot under the soil over
the whole garden . I'm digging up the garden anyway. Perhaps with some
ground stakes here and there connected to the grid, although maybe not
necessary.

The only thing that I can think of why radials are effective is nothing to
do with ohmic resistance to "the earth" or capactive coupling to "the
earth". Not even to do with a large surface area in contact with the ground.
It's simply that the ground is changed, those radials simply make "the
earth" in that locality less like an insulator and more like a conductor.
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?

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).

73's
Richard Clark, KB7QHC

"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

Richard Clark wrote:
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.

mostly due to that epsilon of 80, more than the conductivity


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.

Exactly...

In fact, one can do some numerical analysis to figure out an optimum
strategy, based on minimizing IR losses in the soil. The current
density is higher close to the base of a vertical, so, at first glance,
it would appear that improvements in conductivity there would have more
"value". I imagine there's some nice integration that covers it all.

All that analysis and spreadsheets out there all make the assumption
that you want all radials the same length, which isn't necessarily so.

What also throws a "wrench into the gear train" is that if you start
looking at verticals with nonuniform current distributions, especially
if they aren't representable by a "simple" form such as linear or
cos(h), an analytical approach gets tricky (hence the suggestion for
numerical methods). Consider, for instance, a half wave dipole with the
center, say, 3/8 wavelength above the ground. Or some sort of asymmetric
vertical with an elevated feedpoint, or loading coils. The optimum
radial layout gets a bit trickier to figure out.


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).

73's
Richard Clark, KB7QHC