[TowerTalk] Dayton 2004 Antenna Forum Papers now on the Web!

[Tom Rauch]

Some very interesting food for thought there, particularly
the plots
(figure 15, page 13) showing the change in gain for adding
radial
length.  Fractions of a dB (as in <0.1dB) for going from 0.1
to almost 0.5
wavelength with 16 radials.  Kind of implies that if you
have relatively
few radials (compromise installation), the length is less
critical. >>

I'm trying to think of a way to say this that is accurate
and easy to understand and doesn't make light of any work
anyone has done.

While a model could almost certainly be accurate under
conditions where the soil looks exactly like the model, most
models assume the earth is homogeneous (which earth
virtually never is). One of the least accurate uses of any
model is simulating loss with a wire close to earth.

An early comparison of NEC-2 models to actual FS
measurements of a low dipole someplace under .01WL high (as
I recall). Haggn-Barker did the study in Thailand, and VE2CV
Belrose did the modeling showed about 5dB error. My Beverage
antennas also show significantly more measured current taper
with distance compared to a model.

I'm not sure how later modeling programs behave, but I'd
never count on a model being accurate to more than a few dB
with a wire very close to earth unless the data was
confirmed with actual measurements. Even if a modeling
program is accurate to a fraction of a dB, none of us know
(or could measure) the chacteristics of soil around our
antennas.

I hope we all keep that in mind before counting on fractions
of a dB change!

73 Tom