On 2/2/2011 10:30 PM, Hans Hammarquist wrote:
> I think the idea is that you calibrate the true north against the READING
> on the controller.
But when the rotator is installed it has to be pointed North, or South.
My point is that a compass is not always the best indicator to find
North for an antenna, BUT in the US for *most* areas it will work just fine.
> I believe that declination is rather constant at least in a short time
> frame,
Again it depends on where you live. Here it has changed from zero to 6
degrees since I started flying. OTOH with a tribander or most antennas
6 degrees is "close enough". There are areas around the world that have
changed much more than that over the same period. Fortunately none have
been in the US or even heavily populated areas.
> all you have to do is to direct the antenna in a know direction,
We are talking about finding that "known direction". Here, North is
"that way" and it's close enough. A compass would also be "close enough"
although you can probably eyeball it closer than the compass. But those
areas where the compass is off by 10, 15, 20 degrees, or more it makes a
poor reference without knowing just how far it is off.
73
Roger (K8RI)
|rotate the sensor until you read that direction on the controller.
Unless you have variations in the declination the |reading should keep up.
> (I recommend a north-seeking plastic owl if you have problems finding true
> north:-)
>
> 73 de Hans - N2JFS
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> -----Original Message-----
> From: Rroger (K8RI on TowerTalk)<k8ri-on-towertalk@tm.net>
> To: towertalk<towertalk@contesting.com>
> Sent: Tue, Feb 1, 2011 1:20 am
> Subject: [TowerTalk] A word of caution Was Wireless tower direction indicator?
>
>
> Although the idea is sound, easy to implement in one form or another
> there are many places in the US (and the rest of the world) where
> magnetic and true North differ substantially. The extremes in
> continental US are in the NE and NW. IOW New England states (-20 deg)
> and parts of Washington state(+ 20 degrees) with the East coast running
> -10 and the N Central US down to Mexico and the tip of the Baja
> peninsula running +10. Zero degrees runs from the Sestern edge of
> Hudson Bay to near New Orleans.
>
> http://en.wikipedia.org/wiki/File:IGRF_2000_magnetic_declination.gif
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