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## TRUE NORTH QUERY

 To: TRUE NORTH QUERY n4si@techinter.com (n4si) Tue, 7 Jan 1997 05:02:19 +0000
 ```> I hate to bring this up [but does] anyone know a quick and dirty > way of locating true North? Can it be as simple as adding an x > number of degrees one way or the other to a compass north reading? > > What say you? Mick...W4YV > Is it ever! There is a factor called variation that represents the difference between true north and magnetic north in any given location. All aviation charts (I'm a pilot and air traffic controller so don't you guys nitpick me about RF charts) have isogonic lines (lines of equal variation) printed on them (for those who can't stand not to know everything, the line of 0 variation is called the agonic line). Simply take the variation (expressed as degrees East or West) and subtract or add to the compass bearing to get True North. Which do you do? In aviation we say "East is least and West is best." If you are in an area of 4 degrees West variation, add 4 degrees to your compass heading (in your case, 0 or North) to get the true bearing. That means that if your compass is pointing to the N, you are really pointed at 004. Thus, turn left 4 degrees (so that your compass reads 356) and you will be pointed to True North. Call the FBO (fixed base operator) at your local airport and ask the variation in your area. (From the "more than I thought I wanted to know" department: do not confuse variation with deviation. Deviation is the factor derived from the magnetic effects of the vehicle on the compass installed in it. In aircraft, there is a deviation card next to the compass. No trip can be completely flight planned without access to that information. True Course +- variation = Magnetic Course +- deviation = Magnetic Heading) Has anyone mentioned the North Star? It's at the tail end of the Little Dipper (which is hard to see), but it's "pointed to" by the ends of the "bucket" of the Big Dipper (which is easy to see). Note that this must be accomplished with clear skies AND at night! For the flamers with pens poised, I live practically on the agonic line, I haven't had to correct for variation in 30 years. As a controller, you issue a heading and the airplane flies it. If it looks good on the 'scope, it was the right heading. Variation doesn't come into play. One final thought. HF antennas typically have half-power beam widths of 60-75 degrees. Except in the western U.S. where variation is in double digits, correcting for variation isn't all that important. VHF/UHF? That's another story; some of those beamwidths are pretty tight. 73, Rod N4SI The DXer formerly known as N9AKE (c) 5 November, 1996 -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: K7LXC@contesting.com Sponsored by Akorn Access, Inc & KM9P ```
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