Compass maintainance!

4:43 p.m. on April 22, 2012 (EDT)
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I recently found that my compass had suffered some kind of demagnification while in my rucksack. It is now almost one hundred and eighty degrees out of true. I think this was caused by being stored in proximity to my vhf radio. How can I ensure that this won`t happen again. I always have a vhf radio with me as I am part of a rescue unit. I would love to hear from anybody who could help. Tony Lawlor.

12:05 a.m. on April 23, 2012 (EDT)
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That reversal can happen to compasses that are put in close proximity to an electric field or strong magnetic field. The technique for reversing it is pretty simple in concept, though somewhat tricky in practice. Basically it consists of passing a strong magnet over the compass slowly, producing a reversal back to the correct polarity.

Here is a YouTube of how to do it (not easy to see, though). Somewhere I have a link to a clear explanation of how to do it, which I will try to track down.

1:49 p.m. on April 23, 2012 (EDT)
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This will be interesting to hear more about

4:22 p.m. on April 23, 2012 (EDT)
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Thanks for your reply. Do you think putting either the compass or the vhf in a bag lined with lead foil while in storage would be a help?

9:35 p.m. on April 28, 2012 (EDT)
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Tony Lawlor said:

Thanks for your reply. Do you think putting either the compass or the vhf in a bag lined with lead foil while in storage would be a help?

 No. The problem is not radioactivity or ionizing radiation (which is what the lead-shielded bags are for - protect film, not that anyone uses film anymore ;D, from those airport X-ray machines). The problem is a strong magnetic and/or electric field in close proximity. Remember that radios sent out radio waves, which are one family of electromagnetic waves. Your VHF radio may also have a strong magnet in its speaker, particularly if you can use it as a "push to talk" radio without an earphone. You would do better with aluminum foil, which can act as a faraday cage.

Still trying to find a better re-magnetization article on the web.

One suggestion, though, is to get a higher quality compass. The top quality compasses by Suunto and Silva (Swedish Silva, that is, not the Silva-labelled ones distributed in North America by JWA - the Silva of Sweden compasses are distributed in the US by their Brunton subsidiary. The top quality compasses use a stronger magnetic needle (or cylinder in the case of the "world" compasses), hence are rarely affected by even nearby strong magnets.

6:25 p.m. on April 29, 2012 (EDT)
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I asked a friend if he had the website I thought he had pointed out to me. Instead, he pointed me to my own pontification on the topic, right here on Trailspace! (OGBO slaps forehead and mumbles in his beard).

The only addition I should make is to use a bar magnet, and pass the center toward the north-seeking pole a few times. The magnet's north-seeking pole is the one painted red (or blue, depending on what country it was made in). It is important to get the correct end pointing north, since the Earth's magnetic field is 3-dimensional, meaning it has a tilt that varies with latitude. To compensate for the tilt (called "dip"), the needle will have either a tiny added weight or a tiny hole on the north or south end of the magnet, depending on what "magnetic zone" it was built for. If you are in the wrong zone, the needle will be tilted with respect to the housing, and can scrape the glass or floor of the capsule. This doesn't make that much difference usually, unless you take a compass made in Australia to Northern Canada or take a US compass to Antarctica. "World" compasses have a cylindrical magnet with the needle attached on a pivot, so they do not need the weight balancing.

Main thing with any compass is treat it carefully - don't drop it, break it, or subject it to strong magnetic fields (including electrically generated magnetic fields). Even the best of modern rare-earth magnets can be completely degaussed or have their polarity reversed if you apply a strong enough field under the right circumstances.

I will repeat the advice that you should get a top-quality compass (which need not be expensive - just the right manufacturer). These have stronger, more permanent magnets.

12:57 a.m. on May 1, 2012 (EDT)
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Thanks again for your help. Im after learning a lot about compasses from your reply.Since the occasion that my old compass became demagnetised I have ensured that while hiking with others the person using/carrying the compass does not have either a mobile phone or a vhf in their bag so as not to cause problems with deviation. However, when on ones own this is not possible and we have seen differences in compass readings taken with phone and vhf in your abag and then with the bag removed and placed a few feet away. Your comment about the different qualitiy compass needles is very interesting and I am going to experiment with different brands of compasses to see if this effect can be lessened. Tony.

December 19, 2014
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