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5Ways to Find True North

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5Ways to Find True North 5 Ways to Find True North You can rarely rely on magnetic north to accurately align your antenna. Here’s how to get pointed in the right direction. Compensating for Declination Ron Berry, WB3LHD In the United States, magnetic north varies from –19° (westward error) in Maine to +18° (eastward error) in Washington state. This error is known as Compass Method magnetic declination. World maps, however, are based upon geodetic (i.e., true) north, so to accurately align your antenna, you must compen- If you use the compass method, True north 1 sate for your local magnetic declination. The DXCC Country List at you must first compensate for your (geographic) ok2pbq.atesystem.cz/prog/dxcclist.phpMagnetic provides north helpful coordinates location’s magnetic declination (see −D to navigate this. (compass) the sidebar, “Compensating for Declination”). When your compass Compensation is simple: for a west (negative) declination,N add its absolute needle points north, it is pointing at value to your compass reading; for an east (positive) declination,NE subtract it magnetic north (a point in northern from your compass reading. NW Canada where northern lines of attrac- You may not get your antenna aligned to true north exactly, but most tion enter Earth, responding to its antenna beamwidths are broad enough that you will not see much differ- E magnetic field), not true north (geo- ence with headings a few degrees off. But W remember, if you’re in a location graphically, the North Pole). If you with a high magnetic declination, aligning your antenna to true north is criti- don’t have a standard compass, there cal. Declination error is calculated at 100 feet/degrees/miles, so if you live are many GPS devices and smart- in a location with an 18° declination and align your antenna to magneticSE phone apps that show magnetic decli- north, then try for an 8,000-mile DX contact, youSW will be off target by over 2,700 miles! S nation and true north directions for your location. (A) A National Oceanic and Atmospheric True north True north Administration website (www. (geographic) (geographic) Magnetic north ngdc.noaa.gov/geomag-web/ Magnetic north (compass) +D #declination) makes easy work of (compass) −D finding your declination. Just enter N N your address and the calculator will fill NE NE in the latitude, longitude, and date. NW NW Then hit CALCULATE and the calcu- lator will use the default World E Magnetic Model — which uses the E W geomagnetic field to standardize navi- W gation, attitude, and heading reference networks — to determine your mag- SE SE SW netic declination. The result is shown SW S as a compass overlying a map of your S local area. (B) QS1905-Berry01 (A) For my location, the calculator shows magnetic north (MN) pointing 9° 10' Figure 1 — At (A),True the northabsolute value of a westward declination must be added to the heading shown by the needle (colloquially known as red Fred) to determine true north; west of true north. To get a true north (geographic) Magnetic north at (B) for an eastward declination,(compass) the declination is subtracted from the magnetic heading heading, I must add 9.17° in the east- to determine true north. +D erly direction (see Figure 1A). N 42 July 2019 QST www.arrl.org NE NW E W SE SW S (B) QS1905-Berry01 If you have an easterly magnetic decli- na’s true heading. Your compass dial nation, you would subtract your decli- will have an orientating arrow pointing Equipment nation degrees in the westerly straight out that is colloquially referred If you are looking to buy a new or direction to get the true north heading to as ‘the shed,” along with the red part first compass, some good names (see Figure 1B). Better compasses of the magnetic needle called ”red are Brunton, Silva, and Suunto. have an adjustment bezel to compen- Fred.” Turn your compass dial to “put Try a mirrored orientating com- pass, which makes it easier to sate for east and west declinations. red Fred in the shed” — or align the see where your antenna is magnetic needle with the orienting Once the declination is set, your com- pointed. I also recommend a pass headings will always reference arrow (see Figure 2). While keeping compass with a declination set- from true north. the needle in that position, sight down ting adjustment. Once you set the compass in the direction your your location’s declination, you Assuming that you have a better com- antenna is pointing and read the won’t have to worry about it pass and that it’s now compensated for heading. An orienteering compass again. Remember, if you move to declination, you can check your anten- makes this easier to do. another location, you may need to readjust the declination for that area. For this article and Direction of Antenna testing, I used a Brunton TruArc Shed Housing 20 compass. Figure 2 — A base- E plate compass, which Inches is handy for working with topographic maps. N The compass heading is determined by rotating the housing ring to align the box associated with north S (the shed) with the gen- erally red half (red W Fred) of the magnetic 10 mm north seeking compass needle, colloquially referred to as putting red Fred in the shed. Read bearing here Base plate marker Red Fred QS1905-Berry02 Map Method bottom of the map. Because the Earth’s magnetic field is constantly QS1905-Berry03 2If you have a baseplate compass, Grid you can use a US Geological Survey changing, use this declination only if north the map is current. You may see a vari- (USGS) topographical map (available Magnetic ation of Figure 3 on your map. The star True at www.usgs.gov/products/maps/ north north topo-maps). Orient your map and symbol line is always the direction of compass to true north and take a true north. The magnetic north direc- heading with your compass to an tion is shown with the harpoon line. 7° 36' object you can see. There is an excel- Note the westerly magnetic declination lent video explaining how to do this at number listed as 7° 36' from true 4° 58' www.youtube.com/watch?v= north. There may also be a third direc- a2aGiUl1u4c. tional line called “grid north,” some- times abbreviated as GN. The grid The magnetic declination information lines are references used for navi- and true north direction for the local gating on the map with your baseplate area are generally located at the compass. At street center magnetic variation on January 1, 1985 Annual change of 08' east Figure 3 — Magnetic declination specifi­ cation, generally located at the bottom of topological maps. www.arrl.org QST July 2019 43 Star Method Shadow Method 3 Presently, Polaris, the North Star, 4 On a sunny day, get a QS1905-Berry06 is very close to true north and is rou- straight pole a few feet long tinely used for celestial navigation. In and stick it in the ground as the constellation Ursa Minor, Polaris is straight up and down as pos- the end “tail” star, and brightest of sible. At the tip of the pole’s the seven stars in the Little Dipper. shadow, place an object like a It may be difficult to identify or see small stone as a marker. This clearly on all nights from urban skies first stone is the westerly point. (see Figure 4). Wait about a half hour or more so there is a good spacing For stations south of the equator, W between the shadows and S Polaris is not visible, so you must find place another stone at the tip true south using the Southern Cross of the shadow again. This 1 and the two Pointer stars, Alpha and stone is the easterly point. Beta Centauri, in the constellation 2 Crux (see Figure 5). Placing a straightedge across E N the two stones forms an east- west line. Placing another straightedge perpendicular to Figure 6 — Using the sun’s shadow from a vertical Little Dipper The pole to determine true north. north star the east-west line forms a Pherkad Polaris north-south line with the end Kochab away from the vertical pole pointing Be careful not to blind yourself looking to true north (see Figure 6). Align your directly at the sun. This won’t work antenna north with the boom parallel very well on cloudy or overcast days, with the north-south straightedge. You as the sun’s actual location may be Big must be sure you can see the shadow visually skewed. This calculator is Dipper Dubhe alignment sticks from your antenna good for checking your antenna view. Note that this method will be system from time to time to make Merak QS1905-Berry06 more accurate if the west and east sure nothing has gone askew. points are marked in the morning and Figure 4 — A Northern Hemisphere star map for locating the North Star, Polaris, using the afternoon and are equidistant from two pointing stars Merak and Dubhe in the the vertical pole. Forty-year ARRL member Ron Berry, ladle portion of the Big Dipper constellation. WB3LHD, holds a 20 WPM Amateur Extra- class license and is a member of the Interna- tional DX Association (INDEXA) and the Six Meter International Club (SMIRK). He is on the Southern QS1905-Berry05 Solar Method DXCC Honor Roll and needs only three enti- Cross ties to achieve DXCC #1. Ron graduated from 5An online calculator that displays electronics school in 1969 with a degree in the sun’s azimuth according to the electronics technology.
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