On Sun, 18 Apr 2004 17:48:23 GMT, zeno wrote:
Richard Clark wrote:
The additional ground rods don't do much, RF-wise. You are far better
off with wire laid out radially on or just below the ground surface.
However, what you have is good.

How long should those radials be? and would just a couple be better than none?

Hi Bill,

The current is densest at the feed point for a quarterwave vertical.
Invest copper density in the first eighth wavelength with fewer
radials migrating out beyond there, and so on for as much as you can
tolerate.

The classic FCC grounds run from 112 to 120 quarterwave lengths to
give something like 95% shielding from ground (the point of radials).
Scaling does not follow a strict law of proportionality as 60 would be
85% effective. The proportion is more log based than arithmetic such
that a dozen (roughly a tenth of the FCC standard) would be at least
50% effective. Now, such pencil-whipping is based on abstractions
drawn from full quarterwave radials under a full quarterwave radiator
(classic field work for AM stations). As such, there are a lot of
variables to consider, and yet a dozen, eighthwave long would be a
solid RF ground.

However, few of us have properties that long/wide (without things in
the way) when trying to get into the 160M band game. So ultimately
you do what you can and don't gloat to those who know better. On the
flip side, 160M RF penetration into the ground is substantial and the
traditional ground rods do offer some advantage, and as Reggie offers,
so does the water service - find pipes.

Another myth exploded is when you hear DXers crow about horizontals
have no need of ground systems - they obviously have enough "gain" to
discard the 1 or more dB advantage in a ground screen below their
prima donna antenna.

RF ground serves many functions:
1. A reference to tune against (stability, a sink - what you seek);
2. A shield to reduce ground loss (more gain);
3. A reflector to enhance low propagation angles (more gain).

Please note that number 3 is offered for verticals only, at distances
of many wavelengths away - such is the advantage of shore placed
antennas. As such, "ground" is a misnomer (swamp, lake, ocean, or sea
serves instead) - and ignore the babble about the "conductivity" of
these being so much better. It is the drastic mismatch between the
æther and the body of water that does the DX charm, conductivity is in
the toilet.

73's
Richard Clark, KB7QHC