[FoxHunt] Turnstile antennas for 2M

Thu, 15 Jan 2004 14:51:07 -0500

I always hate to get involved in questions of opinion.  However, this is 
not really"an opinion".

Trees are vertical.  A vertical signal reflects more off the trees.  Yes, 
the tree limbs are rather horizontal but they do not seem to have as much 
effect  as the tree trunks do. The horizontal signal reflects less and is a 
better signal to hunt in dense woods.

Now for some "opinion".  I suspect the Horizontal signal follows the earth 
coverture better than a vertical signal would.

Try it sometime.  Two low po\wer TX, adjust the timing so that they 
alternate the on/off pattern, one on vertical and the other horizontal, 
different ID's or tones  so you can ID each one, but near each other and 
then hunt them.  This effect is much more pronounced when the woods (light 
or dense) are wet from rain or dew.

At 09:17 AM 1/15/2004 -0800, you wrote:
>Never noticed...35 years of transmitter hunting and I never noticed. I 
>guess we don't have the dense forests in California to cause that much 
>attenuation. I will look into it however, and use it on a hide if indeed 
>the V-pol absorption is great.
>All reflections from natural objects tend to make the signal more 
>circularly polarized. I use this technique for mobile hunting with crosss 
>polarized 5 el beams on the 4 runner and note the polarization ratio of 
>bearings to evaluate if they are bounces.
>
>Bob, WB6JPI
>
>[email protected] wrote:
>
>>Marvin is right, if you have ever hunted in deep woods, vertical polarization
>>gets absorbed by the vertical tree trunks. A vertically polarized signal will
>>appear to be horizontal just a few hunderd feet away. The DFing antennas are
>>also have a better pattern when horizontal.
>>
>>Tony
>>AA9CC
>>
>>Quoting Marvin Johnston <[email protected]>:
>>
>>
>>
>>>Horizontal polarization has been used for years on 2M ARDF hunts over in
>>>Europe. From the people I've talked to, there are several reasons that
>>>include less effect from the vertical attenuators out on the course
>>>(trees.) Apparently it is also a bit easier to differentiate between
>>>reflections and the real signal.
>>>
>>>I might add that the signals are AM over there, and not FM as is
>>>commonly used here in the US.
>>>
>>>As far as hiding, ARDF transmitters are identified by an Orange/White
>>>Orienteering flag that are usually visiable from at least 10 or 15
>>>meters away. Unlike some of the mobile hunts I've been on, the idea is
>>>not hider vs hunters, but rather to provide a fair venue for hunters to
>>>compete against themselves. The challange is navigation, not trickery
>>>:).
>>>
>>>If anyone is interested in the Region I ARDF rules, they can be seen at
>>>http://www.ardf-r1.org/, and look under "ARDF Rules".
>>>
>>>
>>>bob wrote:
>>>
>>>
>>>>Why did they decide on horizontal antennas? Verticals are so much easier
>>>>to make, hide etc.
>>>>
>>>>I will be building one and probably use it on an up coming mobile hunt.
>>>>It will make for some very interesting reflections from the bottom of a
>>>>canyon.
>>>>
>>>>I notice that you crumpled the 90 degree phasing harness into a wad and
>>>>stuffed it into the pipe. The outer conductor of the phasing harness has
>>>>lots of RF on it and this isn't a good place to put it. Better to let it
>>>>dangle with the coax. You could also dangle a 1/2 wave loop for a balun
>>>>(although it doesn't have RF on the outside and could be crumpled up),
>>>>removing most of the RF on the feed line.
>>>>
>>>>Bob, WB6JPI
>>>>
>>>>Jay Hennigan wrote:
>>>>
>>>>
>>>>
>>>>>I've assembled a number of these recently.  Details here:
>>>>>
>>>>>http://www.west.net/~jay/turnstile.html
>>>>>
>>>>>Comments, criticism, flames, etc. welcome.
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>
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>>>
>>>
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>>
>>
>>
>
>
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Sincerely,
John Munsey, KB3GK

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