On Thu, 20 May 2004 09:30:07 -0700, Dan Richardson
wrote:

Modeling I found that comparing a full-bore ground system (120
half-wavelength radials) to a single eight-foot ground rod (average
ground) the difference reported was about 1 dB.

Hi Danny,

I made the same comparison at 40M. The difference between 120
(quarterwave) radials and 1 amounts to 0.1dB Clip that one down by a
tenth and the difference climbs to an astronomical 0.3dB.

73's
Richard Clark, KB7QHC

On Thu, 20 May 2004 17:15:01 GMT, Richard Clark
wrote:

I made the same comparison at 40M. The difference between 120
(quarterwave) radials and 1 amounts to 0.1dB Clip that one down by a
tenth and the difference climbs to an astronomical 0.3dB.

Maybe the difference is the length of the radials. I used ½-wavelength
radials as the peak ground current is at 0.35-wavelength from the base
of the monopole - ¼-wavelength radials would be too short to reach
that area.

Danny

Be careful about making generalizations about this. The position of the
peak current depends on frequency and the ground characteristics. I
believe it's also a function of the height of the vertical. In some
cases there's no real peak at all, but an exponential-looking decay of
current from the base of the vertical outward. This, incidentally, was
experimentally measured and documented by Brown, Lewis, and Epstein in 1937.

Roy Lewallen, W7EL

Dan Richardson wrote:

Maybe the difference is the length of the radials. I used ½-wavelength
radials as the peak ground current is at 0.35-wavelength from the base
of the monopole - ¼-wavelength radials would be too short to reach
that area.

Danny

A single ground rod, unless in sea water, has a resistance to mother earth
between 50 and 200 ohms. Let's take it to be 100 ohms.

Efficiency of a 1/4-wave vertical, feedpoint resistance = 37 ohms, is 27
percent.

Efficiency of a 5/8-wave vertical, feedpoint resistance = 50 ohms, is 33
percent.

Efficiency of a 1/2-wave vertical, feedpoint resistance = 2500 ohms, is 96
percent.

The difference in radiation pattern in a typical back yard, in the vertical
plane, is neither here nor there.

The 1/2-wave antenna also needs the most simple L and C matching network.

But I'd never recommend a ground rod anyway. Not worth the time, trouble
and expense unless extremely short of real estate at ground level.

Roy, the problem of choice lies in over-complication by too 'clever',
'knowledgeable' old-wives and gurus rather than under-complication.
----
Reg, G4FGQ