On Mon, 19 Jul 2010 11:58:02 -0700 (PDT), Gsat
wrote:

So now is my question: if a tradeoff must be made, what is more
important, to have an antenna on the clear or to have the best ground
radials system ?

Hi Giovanni,

The best solution is both - in the clear with a lot of radials. The
next best is to raise your antenna, if you can. After that, and
assuming the antenna is ground mounted; then use as many radials as
you can (12 or more); as long as you can make them (usually as long as
the antenna is tall is enough); filling as much area as you can.

Multiband verticals are usually designed to be up at least 3 meters.
Multiband verticals are usually poor performers on their lowest band.

A second question: is it possible to estimate the effect of ground
symmetry and of buildings presence on the antenna radiation pattern
using antenna simulation software like eznec ?

Yes. Do it one band at a time to keep it simple. You will be able to
see the effect, but it won't really amount to much UNLESS you are
comparing very few radials (2,3 or 4) to 12 or more; or to 120. The
change from 2 to 12 will be more significant than changing from 12 to
120.

You will also see the change in shape of the antenna pattern's
azimuth. It may seem significant, but in reality, it will be
overshadowed by other effects like the proximity of buildings.

Modeling the effect of buildings takes a lot of time and experience.
Antenna modelers are an extension of your design capability, not a
substitute.

73's
Richard Clark, KB7QHC