>From: "Roger L. Elowitz" <K2JAS@worldnet.att.net>
>Subject: Re: declination??
>
To: <towertalk@contesting.com>
>>Date: Wed, 23 Oct 1996 01:17:41
>>To: Jamie Tolbert <jtolbert@gremlan.org>
>>From: "Roger L. Elowitz" <K2JAS@worldnet.att.net>
>>Subject: Re: declination??
>>
>>Hi Jamie,
>>
>>My fondest hope is that the person who was concerned because he wasn't
sure how to adjust for the difference between true and magnetic north isn't
the navigator on the dxpedition. Otherwise, he's in big trouble.
>>
>>Just so I can keep things as straight as possible here are a few
encyclopedic quotes to answer your questions:
>>
>> "In order to obtain readings of true north on the magnetic compass, it
must be corrected also for variation, the angle between the magnetic and
true meridians. This angle, also called the magnetic declination, varies in
amount, in direction from east to west of the true meridian principally with
geographical position, and to some extent with time. The amount, direction,
and annual change of the variation for most localities on the surface of the
earth have been determined, and these data are recorded on all charts.
Transient, unpredictable changes in variation occur, mainly in the higher
latitudes, as a result of magnetic storms=20
>>
>>
>>"Compass," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft
Corporation. Copyright (c) 1994 Funk & Wagnall's Corporation.
>>
>>As to whether there is a big difference between the two numbers- well,
that depends on where you are. Here's another encyclopedic quote:
>>
>>"The magnetic poles are located at considerable distances from the
geographical poles. The north magnetic pole is situated in the vicinity of
Bathurst Island in northern Canada, about 1600 km (about 1000 mi) from the
North Pole. The south magnetic pole is near the Ad=E9lie Coast of=
Antarctica,
about 2600 km (about 1600 mi) from the South Pole. The magnetic field at
these poles is vertical. The magnetic poles change location with time, a
phenomenon known as polar wandering, and the direction of wandering has been
observed to reverse. During geologic history the polarity of the earth's
magnetic field has periodically reversed.
>>>
>>>
>>>"Magnetic Pole," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft
Corporation. Copyright (c) 1994 Funk & Wagnall's Corporation
>>
>>The magnetic poles are located at considerable distances from the
geographical poles. The north magnetic pole is situated in the vicinity of
Bathurst Island in northern Canada, about 1600 km (about 1000 mi) from the
North Pole. The south magnetic pole is near the Ad=E9lie Coast of=
Antarctica,
about 2600 km (about 1600 mi) from the South Pole. The magnetic field at
these poles is vertical. The magnetic poles change location with time, a
phenomenon known as polar wandering, and the direction of wandering has been
observed to reverse. During geologic history the polarity of the earth's
magnetic field has periodically reversed.
>>
>>
>>"Magnetic Pole," Microsoft (R) Encarta. Copyright (c) 1994 Microsoft
Corporation. Copyright (c) 1994 Funk & Wagnall's Corporation.
>>
>>Now, if you draw a line from the true north pole through the magnetic
north pole you will have aproximately the "zero declination" or "zero
variation" line. Here in New Jersey the magnetic variation amounts to about
ten to eleven degrees Westerly variation. Depending on where in the
Carribean this guy is, my guess is that the magnetic variation would be
somewhere between three and five degrees Westerly variation meaning that the
navigator would have to add those three to five degrees to his compass
reading to find his true heading. The three to five degrees is just a rough
guess on my part.
>>
>>Being off course three to five degrees in the open ocean over the course
of hundreds of miles can make all the difference of ever making landfall or
not. I wouldn't worry very much about this guy however. Only a complete
idiot would go traveling around the Carribean in any decent sailing vessel
without a substantial knowledge of navigation. Otherwise, he'd surely get
what he deserves- don't you think?
>>
>>Of course, set your antenna bearings for true readings. To find your true
bearings you can consult a survey plot of your house. Otherwise you'd need a
compass and an aeronautical chart which will show your local magnetic
variation. A call to your local general avaition airport will bring the
correct answer rather quickly. Then, just add the variation to the compass
reading and you'll know which way your house faces.=20
>>
>>I've determined from charts and survey plots that the back of my home
faces 34 degrees. I line up the director of my beam parallel with the edge
of the roof and I preset my rotor control for that reading. I then lock the
beam on the mast for that heading and... thats it. Simple. I hope. Sorry,
but I can't be of much help regarding antennas and reception angles. =20
>>
>>Hope I've been helpful.
>>
>>73's de Roger, K2JAS
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>> =20
>>At 12:05 AM 10/23/96 +0000, you wrote:
>>>Today I heard a carribean dxpedition for the cqww concerned because he=20
>>>wasnt sure how to adjust for the difference between true and magnetic=20
>>>north...Is there really a big difference?? I think for my latitude its=20
>>>around 4 degrees..Should ones antenna be set for true or magnetic north??=
=20
>>>Also a W0 on one of the reflectors( I hope this one) mentioned that=20
>>>while experimenting with a 1/4 wave sloper they got a significant signal=
=20
>>>strentgh difference on rx while adjusting the angle...what does work=
best??
>>>wouldnt it depend on the incoming signal angles?? wont it change as=20
>>>propagation condx change??73 Jamie WW3S
>>>
>>>
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>>
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