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Magnetic North Versus Real (True) North:

Wim Dewilder (K6TE) on July 26, 2003
View comments about this article!

It just struck me to check the magnetic deviation of a compass in my QTH near San Francsico.

It turns out that real north is 15 degrees off from where the compass points !

So that means my beam has been pointing 15 degrees off from optimal. Luckily the radiation pattern of my KLM KT34A is pretty wide ...

And me who was trying to get that thing pointed optimally to the station I was talking too ;-)

here's a map that shows the deviation http://www.geo-orbit.org/sizepgs/magmapsp.html#anchor598933

73 de K6TE Wim.

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Magnetic North Versus Real (True) North:  
by WA4MJF on July 26, 2003 Mail this to a friend!
I guess this is why there are compass cards.

If you're gonna use a compass, be sure to field
check it with a map. That's one reason a lotta
LTs get lost, glad I was a Sergeant before I
was a LT :-)

73 de Ronnie
 
Magnetic North Versus Real (True) North:  
by KG4OOA on July 28, 2003 Mail this to a friend!
I spent some time near Fairbanks, Alaska. The deviation is better than 30 degrees up there.

You learned a valuable lesson. There are other corrections that need to be made for flight planning and so forth. You don't have to worry too much about them at this point maybe later.

It is important to know the point of reference being used.

If you want to have real fun try the UTC coordinate system. It is great once learned but it can be a little difficult in the begining. Using that system I can pin point the location of your shack accurate to 1 meter.

Have fun and 73,

Bob
 
Magnetic North Versus Real (True) North:  
by W7PHX on July 31, 2003 Mail this to a friend!
If you want to calculate the current magnetic declination at your location, you can go to http://www.geolab.nrcan.gc.ca/geomag/cgrf_e.shtml and use their magnetic declination calculator.

The magnetic pole is always slowly moving and the actual declination depends upon what point in time you are talking about. The calculator at the referenced site will let you specify your latitude and longitude and the year for which you want to know the declination.

You probably won't see much difference from the 1990 maps, however, since the movement of the pole is slow.
 
Magnetic North Versus Real (True) North:  
by K3SI on August 2, 2003 Mail this to a friend!
Does GPS know the difference?
 
RE: Magnetic North Versus Real (True) North:  
by N2ERN on August 3, 2003 Mail this to a friend!
You are confusing your terms.

VARIATION is the difference between true and magnetic. It's based on your location, and doesn't change with the way you're facing.

DEVIATION is the error caused by your immediate surroundings; on a boat, for example, it may include anchors, electronic equipment, fittings and the like. Deviation will vary with the heading of the boat, or, in other ways, the way you are facing. One would make a DEVIATION TABLE to know the adjustment.

An excellent discussion of the subject is at:

http://home.att.net/~agligani/navigation/magnetic.htm
 
Oh, you're not on a boat?  
by N2ERN on August 3, 2003 Mail this to a friend!
Chain link fences, steel outbuildings, cars in the parking lot, that H-T on your belt -- all contribute to DEVIATION.
 
RE: Oh, you're not on a boat?  
by AD7DB on August 6, 2003 Mail this to a friend!
What's interesting is that on some aircraft maps, it notes that a magnetic variation of up to (n) degrees may exist in a certain area. I've sometimes wondered why.
 
RE: Oh, you're not on a boat?  
by N2ERN on August 6, 2003 Mail this to a friend!
Don't confuse Variation with Deviation. Variation is fixed, depending on ones location along the magnetic lines of flux. Navigation charts (aeronautical, marine and topo (which shows it in a "declination diagram")) are always printed in TRUE. You must add or subtract the variation (declination) printed in the legend box or in the compass rose printed on the chart to arrive at the Magnetic heading or bearing. Topos say that the declination is based on the applicable number in the center of the chart. Aero would be similar. The much larger area covered by aero charts would be the reason for the approximation statement.

It's all pretty moot today. GPS headings are in true, b3ecause they don't depend on the earth's magnetic field for accuracy. Magnetic compasses have become more or less outmoded today.
 
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