SV: [FoxHunt] Polarization, was Turnstile antennas...

[Jay Hennigan]

On Fri, 16 Jan 2004, Jon Sletvold wrote:

> In Norway we're using a horizontal circular antenna that is 1-lambda, that
> generates a horizontal e-field according to the int ARDF rules. I've seen
> other veritcal designs, but from my point of view "our" antenna a better
> design for those that have to walk their way through the wood with antennas
> and transmitters in the bakcpack - rugged and easy deployable as it is.

It sounds like what is typically called a "halo".

A crossed-yagi 2m turnstile is relatively easy to pack in if the elements
are removable.

> I have never thought of using the polarization as an excuse of not finding
> the transmitters, but I'll keep that in mind the next time I'll get lost!

According to KE6HTS someone has beaten you to it.  :-)

> My opinion is that the challenge of 2m ardf is to decide the direction to
> the transmitter vs reflection. A reflection will be of any polarization and
> weaker than a directe wave. I don't think the polarization of the antenna
> is realy an issue, but more of a "religious" discussion as Jan says.
>
> However my fellow ARDF runner LA5OBA heard from our Swedish ARDF friends,
> that using the polarity is a mean of detecting direct wave vs reflection by
> turning the antenna 90 degrees (to vertical pol.). A direct wave should
> give som reduction in signal strenght while a refelcted signal should not.
> I have tried this during my ARDF cometitions without beeing able to detect
> a significant bearing detection, but it might be worth a theoretical
> discussion?

This is indeed valid.  If the polarization is known, the hunter can
make decisions by the behavior cross-polarized as opposed to in the
same polarization.  If you have a direct path, you will indeed see a
drop of several dB going cross-polarized.

Where it becomes a challenge is where you have no direct path, such as
if there is a hill between you and the transmitter.  The hunter has to
take the best of several bad bearings.  Even there, a lobe that shows
a drop in strength going cross-polarized is usually more reliable than
one that does not.

I still think that the absolute polarization whether horizontal or
vertical is not a major factor as long as it is known.

> Our program and concerne this year is recruting and equipment. I've seen
> several design throughout but no ready availabel kits, and no one that are
> environmentaly compatible with Norwegian rain. A will write a report on our
> web site from our annual ARDF techincal meeting Saturday 17. about
> recruting and technical issues  in Norway (I'll make an english version).

URL, please!

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