

determining azimuth with a compass

Greg KO6TH wrote:

In my case I used the shadow of the sun on the back of the dish to calibrate the rotor position (a compass is not good enough), and now I have no problem finding the beacon with a little twist of the radio dial.

Wayne W9AE replies:

I can reliably calibrate the azimuth within 2 degrees using the Silva compass that I used as a Boy Scout.  A compass IS good enough if you:

1.	Use a compass that has a good azimuth scale on its bezel.
2.	Use the compass away from ferrous metal.
3.	Know your magnetic declination.

Magnetic declination is the difference between TRUE north and MAGNETIC north in a particular location.  If you don't know your magnetic declination, do a search on Google to find any number of web sites that have magnetic declination maps and/or calculators.  My favorite site is run by the Canadian Geological Survey:
http://www.geolab.nrcan.gc.ca/geomag/e_magdec.html <http://www.geolab.nrcan.gc.ca/geomag/e_magdec.html>    Click on the MIRP link to get to the calculator.  With the calculator you can even see how your magnetic declination has changed over the years as the magnetic north pole drifts around northern Canada.

There are areas where a compass isn't reliable - near the magnetic north pole, or in areas that have an extremely high iron content in the soil (e.g., the "Iron Range" in Minnesota).  But a compass is reliable in MOST places, and works ALL the time.  It works at night (when the sun can't be used).  It works when it's cloudy (when the sun and moon can't be used).  It doesn't require batteries (like a GPS).

Wayne Estes W9AE
Mundelein, IL, USA