[FoxHunt] Polarization, was Turnstile antennas...

[Jay Hennigan]

On Fri, 16 Jan 2004, Bruce wrote:

> I was simply going by the plots that my original Yagio optimisation
> software plotted. It gave both horizontal and vertical plots. It seemed
> the horizontal always gave a better front-to-rear ration (not the same
> as front-to-back ration) and a better shaped forward lobe. Maybe the
> effects in practice are too subtle to notice, but teams here still mount
>   their car Yagi antennas horizontally even though the signal
> transmitted varies between horizontal and vertical.

Interpreting E-plane and H-plane plots can be misleading when transposed
to field direction finding.

The "horizontal" plot of a vertical ground-plane antenna is a circle.  It
has a front-to-back ratio of zero.  The "horizontal" plot of a vertically
polarized yagi rotated in azimuth, if "better", would argue that better
bearings will ensue with vertically polarized antennas.

The "vertical" plot of a vertically polarized yagi represents the
relative field strength with respect to elevation above or below the axis
of the boom.  If the yagi is rotated so that the elements are horizontal,
then the (worse) "vertical" pattern will represent azimuth.

> The forest refections were something I hadn't considered, but may well
> be a factor.

I would suspect that if the actual polarization of the antenna in real
field conditions were hidden from the observer, most ARDFers would be
unable to tell whether the hunting and hidden antennas were both vertical
or both horizontal in typical terrain.  It is relatively easy to tell if
you are cross-polarized with respect to the transmitter much of the time,
but the absolute polarization would, in my opinion, be very difficult to
judge in a double-blind study with a typical tape-measure beam in typical
ARDF venues.

This is likely to degenerate into a religious issue along the lines of
Coke-vs-Pepsi or the audio qualities of $300 solid silver power cords for
stereos, Telefunken 12AX7s, and green Magic Markers.  Maybe we should
just agree that we hunt horizontal in ARDF because those are the rules.

> Also, what is it with pine trees and 6m ? If anyone has ever tried to DF
> 6m whilst in a pine forest they'll know what I mean !

Well, it's kind of hard to run fast carrying a three-element beam...  :-)

-- 
Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net
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