[FoxHunt] Turnstile antennas for 2M
bob
[email protected]
Thu, 15 Jan 2004 12:59:01 -0800
John Munsey, KB3GK wrote:
> 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.
I agree that it is logical...just that I have never obbserved it. I will
be looking.
>
>
> Now for some "opinion". I suspect the Horizontal signal follows the
> earth coverture better than a vertical signal would.
This is true, but only true for relatively long distances where the 4/3
earth model applies. With 2 meters this is 30 or more miles and not
something that ARDF would be interested in.
>
>
> 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.
I am building the turnstile antenna as it is similar to a 1/2 wave
vertical in gain and pattern and I will compare them and publish here.
Bob, WB6JPI
>
>
>
>
> 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.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>> _______________________________________________
>>>>> FoxHunt mailing list
>>>>> [email protected]
>>>>> http://mailman.qth.net/mailman/listinfo/foxhunt
>>>>>
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>>>>
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>>
>>
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>
>
> Sincerely,
> John Munsey, KB3GK
>
>
>
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