[amsat-bb] Re: How to calibrate the azimuth angle?

[Bruce Bostwick]

Not meaning to trash compasses, just have had some less than  
satisfying experiences using them to align antennas on satellites due  
to the number of sources of measurement errors that have to be  
accounted for.  I've used some very good compasses (my favorites are  
the ones from Morin that allow sighting across the compass to get a  
magnetic bearing of a landmark on the horizon :) but getting accurate  
true north out of even a good magnetic compass is a lot of work ..

On Dec 27, 2007, at 7:15 PM, Jeff Mock wrote:

> Well, now that everyone has trashed compasses.  Here's the compass  
> that
> I really really like:
>
>    http://www.suunto.com
>
> Click on "precision instruments", it's the Suunto Tandem.  It's a
> compass and clinometer in a nice machined aluminum package.  It has
> optical sites for both instruments that really improves accuracy (if  
> you
> ask me). It's really well made and it's from Finland...  If nothing
> else, you can walk around measuring the height of trees.
>
> jeff
>
> Bruce Bostwick wrote:
>> A compass won't give you accurate azimuth unless you know for sure
>> that you're not near any large masses of metal, and even then, you
>> will need to know your local magnetic deviation.  I tried to use a
>> compass to align a satellite dish once, and it put me so far off on
>> the azimuth I never did find the satellite that way, even taking
>> magnetic deviation into account.  You might have better luck where  
>> you
>> are, but it's a lot of work to do it that way even if it does work.
>>
>> A much easier solution is to look at your location in Google Earth  
>> and
>> find the orientation of a nearby road, and use that as your azimuth
>> reference.  That automatically gets you azimuth relative to true
>> north, which makes the job considerably simpler.  If you don't have
>> nearby roads that are straight enough to be useful, find a distant
>> visible landmark (like a radio tower) and determine what its azimuth
>> is from your location, then use it as a reference point and find your
>> desired azimuth from there.  (A long time ago, I worked out a formula
>> for determining the bearing to a distant landmark using only the
>> latitude and longitude of it and the observing location.  It's on
>> paper somewhere, unfortunately I don't know where and I'd have to  
>> redo
>> the math at this point.  But if you're interested, let me know.  It's
>> not too difficult to measure the orientation of the baseline between
>> the two using Google Earth though ..)
>>
>> On Dec 26, 2007, at 11:08 PM, Chiu-Teng Tsai wrote:
>>
>>> Dear all,
>>>
>>> I am Chiu-Teng Tsai (BM6ERA) from Taiwan. Now we are building a
>>> mobile ground station. One of our problem is how to calibrate the
>>> azimuth angle. Use compass only, or any better solution? Thanks for
>>> your help!
>>>
>>> Best regards,
>>>
>>> Chiu-Teng Tsai
>

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