Richard Fry wrote in
:

On Oct 1, 12:45 am, Owen Duffy wrote:
....
Using NEC-4 to incorporate buried (or elevated) radials into the model
should show groundwave fields within 1 km of the monopole that are
very close to the theoretical maximum for the applied power when
radiated along a perfect ground plane, if the model is optimal, and
accurate.

It may do, I can not comment. My interest is for an antenna for sky wave
path, and I have not explored ground wave performance.

In the cases of 32 buried radials and three elevated radials, the
patterns are similar, efficiencies are similar, and maximum gain is
similar. Reducing the number of buried radials degrades its performance
significantly.

The elevated radials configuration allows a shortened radiator with
capacity hat with negligible degradation in performance. I haven't
modelled the same thing over buried radials, but I expect performance
degradation would be significantly worse.

Owen

On Oct 1, 3:02*pm, Owen Duffy wrote:
Richard Fry wrote:
Using NEC-4 to incorporate buried (or elevated) radials into the model
should show groundwave fields within 1 km of the monopole that are
very close to the theoretical maximum for the applied power when
radiated along a perfect ground plane, if the model is optimal, and
accurate.

It may do, I can not comment. My interest is for an antenna for sky wave
path, and I have not explored ground wave performance.

Just to point out that for vertical monopole heights of 5/8-lambda and
less, the peak elevation plane relative field (E / E max) _always_
occurs in the horizontal plane, regardless of the r-f losses in the
buried radial system or counterpoise wires they are driven against,
and the conductivity of the earth in which those radial wires are
buried, or above which they are elevated.

IOW, the relative field actually "launched" at all angles above the
horizontal plane from such antenna systems _always_ is LESS than that
in the horizontal plane. The reason for this is related to the r-f
current distribution, and its relative phase along the lengths of
those monopoles.

NEC analyses showing low to zero relative field in the horizontal
plane being launched by a monopole of 5/8-lambda height and less and
regardless of the r-f ground they are driven against need to be
understood in due context. The link next below leads to further
development of this ...

http://i62.photobucket.com/albums/h8...at_Compare.gif

The longest, great-circle, single-hop, skywave paths are related to
the relative fields launched by a monopole system at elevation angles
of less than ten degrees (see Figure 55 in the link below) -- where a
NEC analysis may show very low relative field.

But if such low relative fields really were true for the fields
actually launched by such monopoles, then the nighttime skywave
coverage of MW AM broadcast stations would be much different than is
shown by real-world experience (and applicable theory).

http://i62.photobucket.com/albums/h8...Comparison.gif

RF