At 08:19 AM 11/12/2006, Jim Jarvis wrote:
>I understand the notion of the physical response patterns
>of verticals and horizontals. And, I would agree with Jim lux's
>observation about groundwave absorption.... except for the
>question of how rapidly it falls off, and whether in the
>relative near field (10 wavelengths or so from the antenna) that
>absorption is sufficient to attenuate the horizontally polarized
>noise signal.
One could probably find out more than one wants to know about
"surface waves" "Zenneck waves", etc., at
J. Zenneck, Ann. der Physik, 23, 846--866 (1907)
And a more useful reference is probably
D. A. Hill and J. R. Wait, ``Ground wave attenuation function for a
spherical earth with arbitrary surface impedance,'' Radio Sci. 15,
637--643 (1980)
I haven't seen either one.
A quick reading over of some other references, though, shows that
Hpol propagation is substantially more complex than a simple "uniform
field over a uniform conductive half space" that Zenneck and
Sommerfeld wrote about 100 years ago. There are diffraction effects,
scattering, not to mention reradiation from other structures and
things (trees, bushes, furrows in fields). Given that we don't
usually have our antennas in the middle of a nice flat plane (N6RK's
antenna farm out in the California San Joaquin valley probably
excepted... there's entire 7.5 minute topo quads with no contour
lines on them out there), it might be MUCH different (at least in some cases).
Seems that it's a whole lot more complex than at first glance, and my
practical experience says that when there's that much literature, the
difference from the simple theory is probably bigger than 10-20
dB. (If it was a tenths of a dB thing, it wouldn't be as
"interesting" to the theoreticians.. it would just be conference
papers about little calibration issues.)
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