Azimuth Maps & Magnetic Declination Corrections in the Field.
by Randall Tom (W7UDT)
According to the USGS website (which is wrong!), in the United States, the current magnetic declination can be found below.
Here’s the USGS link: https://www.outdoors.org/resources/amc-outdoors/outdoor-resources/what-is-declination/
Did you know that magnetic north changes over time? And with that, magnetic declination changes over time! The link below is from the organization Alpine Savvy. Apparently, both have change dramatically.
https://www.alpinesavvy.com/blog/find-the-correct-declination-for-anywhere.
Their website has a chart showing the change at Portland Oregon. It illustrates a dramatic change since 1900 to today, from 14° East to 22° East (currently), a full 8° difference over time.
Bear in mind, magnetic declination has a greater, more exaggerated variance and effect closer to the equator.
So what does it mean for the Ham rotating a large beam? Everything. Everything should be based on current data, specific for their location. It matters.
For the correct current magnetic declination information on your location, go to: https://www.magnetic-declination.com
Many of the online references, even those at the USGS website are incorrect. Printed maps, topographic maps, are often incorrect.
Accordingly, you’ll need to orient your Azimuth map, and your antenna orientation! In my case, 12° 52′ East in Boise… Not 15° East as shown on USGS references.
It may not seem as important in HF field operations, given many field operators utilize wire antennas and therefore antennas orientation is less impacted by precise magnetic declination. But you need to understand these changes, in declination and magnetic north are, in some way, connected to the Sun and its influence on radio propagation, and the earth’s geomagnetic fields.
As an example… In WW2, the US Navy torpedoes often failed to detonate properly due to their magnetic proximity fuse detonators. The problem: They were not properly calibrated to their respective lat/long declinations. A simple oversight, or a misunderstanding with profound implications. Its costs were incalculable and directly affected the war effort.
Per my previous post, “The World is flat! Just ask any Ham!” I’d encourage you to visit NS6T.net, print out a correct azimuth map for your location, and get your current magnetic declination, and adjust accordingly.
Well then, there ya go… Shoot straight, Good DX, and 72!
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While your point about the Magnetic North Pole moving over time, and declination with it, is very valid, your antenna should still be pointed “15° East”.
Your Azimuth Map is built using True North, not Magnetic. And you should be aiming your antenna using True North coordinates.
Declination only comes into play when you use a magnetic compass to figure out where True North is when laying out your antenna and configuring your rotator software.
Ah! You may be right… We’d have to see if the Azimuth Map was generated correctly. Great ‘point’ (get it?).
Thanks for the comment. Late night authorship is fraught with error.
72 de W7UDT ID sk ee
I immediately recognized the blue map at the top of your post as inaccurate! (As you then point out in your text.) By the way, the “USGS link” that you give goes to outdoors.org, not USGS.
Interesting to note, in just the past few days I was thinking that I had not checked my magnetic declination lately. My Suunto compass is currently set for three degrees west, which turns out to still be accurate, so all good here.
I worked in the mining industry developing mining projects. The use of my Brunton transit was key to lots of what I did in the field.
An older, wiser geologist taught me how to trace magnetic deflections and map certain deposits or geologic structures with my Brunton. It’s one of my treasured possessions.
Good thing I was in Northern latitudes away from the equator, where magnetic forces are stronger, or who knows how lost I’d be!
Thank you for the interesting post.
My malware browser gave warning messages “Website blocked due to phishing” for both links you give in the article.
Can you please check these links.
Best,
John
Not trying to be funny, but the Earth’s magnetic north pole is somewhere in the South Antartic. Just north of Canada is the Earth’s magnetic south pole.
Wow! Another piece of the puzzle. Thanks.
Edit to above comment: the current author gets it right (doesn’t write “magnetic north pole” but “magnetic north”). It was one of the links I was a bit peeved at.