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

[bob]

I use this technique and it works quite well. In my mobile hunting 
vehicle I have a 10 element cross polarized beam (5 elements in each 
polarization). I note the difference between the two antennas for each 
bearing. When I am where I think may be a clear shot, ie one where I am 
high and clear, I will log the ratio and compare it with subsequent 
bearings. All reflections are more circularally polarized than the 
direct path.  Now ther is an issue with horizontal polarization and you 
are looking into the side of a long yagi. This signal will be direct and 
is vertical and most reflections are horizontal. But that is an 
exception and not applicable to ARDF.

My concern with using H-pol is the restriction it places on the more 
advanced DF techniques such as are used in LOJAK and VHF ocean 
navigation as well as eliminating doppler, TDOA and other ham DF 
equipments which do not function well for H-pol. It really restricts you 
into carrying large beams (for VHF) or other structures that are big 
enough to have gain and therefore lobes. I can imagine TDOA devices that 
are as small as 6 inches that will have sufficient sensitvity and 
accuracy for ARDF use and light and functional to be worn like 
eyeglasses. But they would be severly restricted by the use of H-pol in 
that the antenna structures would not have adequate sensitivity.

Bob, WB6JPI

Jon Sletvold wrote:

>Hello all.
>
>Just a small reflection (not radio refl.:-)
>
>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.
>
>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! 
>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?
>
>--
>
>Anyone for cross country ski ARDF (Bruce?). I'll keep you oriented on 
>www.ardf.no.
>
>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).
>
>Ha en fin dag!
>(Have a fine day)
>
>Jon / LA9NGA
>
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