NEC-LIST: Re: QUESTION

Don Belcher wrote:
>...it sure looks like the horizontal is radiating a lot more
>integrated power than the vertical (meaning it looks like the overall
>radiation efficiency of the antenna/earth "system" is higher with the
>horizontal). Of course the overlays are at the broadside azimuth for the
>horizontal....
>Is there some factor of 2 or something similar that I am missing or
>is it all pattern effects and fooling me bacause I am looking at the
>horizontal's best azimuth?

I believe that _most_ of the difference that you see is due to your
implicit assumption (which you already doubt) that the horizontal
dipole is azimuthally omnidirectional, as the vertical dipole is. In
other words, yes, you are looking at the horizontal's best azimuth.

That said, (IIRC) a horizontal dipole really does radiate (into the
far field, by definition) slightly more efficiently than a vertical
dipole, because the vertical dipole puts more power into the ground,
where it's lost. The difference depends on the height of the antenna
above ground because, if the near field of the antenna extends to the
ground, then the near field induces power-dissipating current in the
ground, too. Using NEC-4 I once evaluated this effect for a 14-MHz
vertical dipole above poor ground, by numerically integrating the
vertical component of the Poynting vector over the ground surface.
IIRC, when the lower end of the dipole was around 3 m above ground,
the ground loss was of the order of 0.5 dB. I'm sure it was less
than 2 dB. The only thing that I recall with certainty is that it
was not enough to justify covering the ground with copper. :-)

-Chuck

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