K1TTT Technical Reference

Friends in Radio Land,

I have agonized enough, watching this discussion about magnetic variation.
The information needed can be found on a map from the Defense Mapping 
Agency (they have a 800-number).  In fact, they have a full set of 
geomagnetic maps for those interested.  But for magnetic variation, ask 
for DMA Stock No. WOBZC42.  I don't recall the price but if you're 
serious, it is not unreasonable.

For some typical values, consider the following for the compass variation:

                Seattle         22 degs E of North
                Bismarck. ND    10 degs E of North
                Chicago, IL      1 deg  W of North
                Detroit, MI      6 degs W of North
                Buffalo, NY     10 degs W of North
                New York City   15 degs W of North
                Los Angeles     14 degs E of North 
                El Paso, TX     10 degs E of North
                New Orleans      3 degs E of North
                Charleston       5 degs W of North
                Wash, D.C.      10 degs W of North

That ought to get you oriented.  Now the next question is the width of 
your antenna pattern.

73,

Bob, NM7M

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For those concerned with determining the magnetic declination (or variation)
for your QTH, be advised that the figure shown on your local USGS topo quad
map may be over 25 years out of date.  The magnetic declination does change,
albeit slowly, with time.  Even the FAA sectional aeronautical charts at
times display figures up to 6 years out of date.

Try this online calculator, courtesy of NOAA, U.S. Dept. of Commerce*:
http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/fldsnth1.pl

It is educational, even if you do not need the precision offered, which
indeed you don't for HF work.  This seems to be based upon the same
mathematical model that is used for generating the values on the government
maps.

*I am not affiliated with the U.S. Gov't. nor do I stand to profit from any
association with it (ha).

73,
Charley, K7NW




"At the time (local) half way between local sunrise and local sunset,
the Sun, if shining, will cast a shadow exactly (true) North-South."

That's the sentence.  

Now, to avoid the FLAMES I received last time:  No, I do not mention
NOON and this has nothing at all to do with noon, anywhere.  Yes, this
works in the Southern Hemisphere, the shadow will fall to the South,
however.  Yes, this works in Alaska (when the sun is out). Yes, if you
live in Death Valley or behind a hill, you won't be able to use this.
And finally, no, it will not work on the Moon, and it will be difficult
on/near the Earth's Equator.

Example:

local sunrise = 0700
local sunset = 1720

The sun will cast a shadow N-S at exactly: {(1720-0700)/2} + 0700 =
1020/2 + 0700 =
510 + 0700 = 1210 local time!

Just use the local weather forcaster's sunrise/sunset times and it's
accurate for amateur antenna alignment for sure!

73!

Bill, N3RR





---------
True north is compass north plus or minus deviation (that's magnetic north)
and plus or minus variation (the difference between the north pole and
magnetic north). That's the book method.
The easy method for hams, and as a one-time navigator I'd endorse, find the
star Polaris, the North Star, and true north is within a degree of the
heading from you to Polaris. If you can find the Big Dipper it's easy.  The
outer two stars in the dipper (away from the handle) point to Polaris.
                              Stu Greene WA2MOE 
                            7537 North 28th Avenue
                          Phoenix, Arizona 85051  USA

                              wa2moe@doitnow.com                           






M. Gray, And the TRUE NORTH crowd: Well I am going to put this 
little tid bit of info into 
your data stream just to clue you in. First of all if you are not 
into laying out boundary lines for legal discription, then the East 

West varition  will suffice for the rest of any normal day to day 
requirements. I have over 20,000 hours pilot time with 125 trips 
around the world. Plus I flew out of Resolute Bay in The NWT of 
Canada in 72/73 and we used to fly over and into a ice strip at the 

magnetic North pole and sit on the ground in the Electra while we 
were unloading fuel and WATCH THE WHISKEY COMPASS GO ROUND AND 
ROUND SITTING STILL ON THE GROUND PERIOD. We used modified GRID 
navigation in those latitudes and used ASTRO Compass to shoot sun 
lines/moon/planets to get True lines shooting for headings to a 
landing strip. We had to use the correct charts for 
time/declination and bodies(not human) to get a track.

MY POINT IS AND I HAVE SAID IT BEFORE LOUD AND CLEAR. What you are 
doing on HF is like trying to get the fly shit out of the black 
pepper with an electron microscope, when the pattern for the 
antenna or path in question has an agle bandwidth of 30 degres or 
more at takeoff. unless you are at 10 gig's or light.
East is least and west is best and 13 degrees in LA don't mean S--T 

at HF.

So if you live in a normal city in the USA you can nearly bet that 
the streets run No./So. and EA./WE. so close to what you need to 
know about WHERe true north IS. bye the way THERE IS A Star up 
there in the sky called the NORTH STAR, and if you can find that 
you can point your Antenna or what ever to TRUE north. Were you 
ever a Boy Scout? One of my merit badges was to find stars/planets 
etc.

At 10gig to 25 gig's we are now talking a whole new story. Try Star 
TRek. I worked on Gene Rodenberrys Satellite system before he went 
on his own Trek mission. You know what he could care less where 
TRUE NORTH was.

Talk about BANDWITH 
Hank







OH NO!!!!  Not this again!  Get a boy scout to show you the big dipper
and locate the north star (polaris)   
You can easily be off 30 degrees with a compass.






Gary,
Call your local airport control tower or FBO, and ask them what the 
magnetic declination is for your area.  This is the difference in degrees 
between true north, and magnetic north.  It drifts slightly each year, 
but not amounts of concern for antenna pointing.  In Richmond, VA a 1965 
map I have, shows the declination as being 13.5 west; That is, true north 
is really east of where the compass needle points by 13.5 degres.  Annual 
change in 1965 was 5 minutes westward per year.
Good Luck, de Pat, AA6EG  aa6eg@tmx.com





Is it ever! There is a factor called variation that represents the
difference between true north and magnetic north in any given
location. All aviation charts (I'm a pilot and air traffic
controller so don't you guys nitpick me about RF charts) have
isogonic lines (lines of equal variation) printed on them (for those
who can't stand not to know everything, the line of 0 variation is
called the agonic line).

Simply take the variation (expressed as degrees East or West) and 
subtract or add to the compass bearing to get True North. 

Which do you do? In aviation we say "East is least and West is
best." If you are in an area of 4 degrees West variation, add 4
degrees to your compass heading (in your case, 0 or North) to get the
true bearing. That means that if your compass is pointing to the N,
you are really pointed at 004. Thus, turn left 4 degrees (so that
your compass reads 356) and you will be pointed to True North.

Call the FBO (fixed base operator) at your local airport and ask the 
variation in your area. 

(From the "more than I thought I wanted to know" department: do not
confuse variation with deviation. Deviation is the factor derived
from the magnetic effects of the vehicle on the compass installed in
it. In aircraft, there is a deviation card next to the compass. No
trip can be completely flight planned without access to that
information. 
     True Course +- variation = 
          Magnetic Course +- deviation = 
               Magnetic Heading) 

Has anyone mentioned the North Star? It's at the tail end of the 
Little Dipper (which is hard to see), but it's "pointed to" by the 
ends of the "bucket" of the Big Dipper (which is easy to see). Note 
that this must be accomplished with clear skies AND at night!

For the flamers with pens poised, I live practically on the agonic 
line, I haven't had to correct for variation in 30 years. As a 
controller, you issue a heading and the airplane flies it. If it 
looks good on the 'scope, it was the right heading. Variation doesn't 
come into play.

One final thought. HF antennas typically have half-power beam widths 
of 60-75 degrees. Except in the western U.S. where variation is in 
double digits, correcting for variation isn't all that important. 
VHF/UHF? That's another story; some of those beamwidths are pretty 
tight.

73, Rod N4SI
    The DXer formerly known as N9AKE
         (c) 5 November, 1996

> Sponsored by Akorn Access, Inc & KM9P
Down-load a copy of GeoClock....Wait for the sun to shine, have a 
bunch of sharp sticks, and build your own Stone Hedge..to late at nite
to
spell good....




1) Call the closest airport and ask for the magnetic offset information to
correct your compass heading.  Compasses are not very accurate, though.

2)  Sight Polaris (the North star).  For the most accurate determination
you will need to know the offset from The Nautical Almanac or at least
the time for meridian crossing.

3)  Look for your local sunrise and sunset times in the newspaper
and split the difference for local sun noon (meridian crossing) and the 
shadows are true north.  (See software in the ARRL Handbook --
1997 ed. for the program NSHADOW.BAS to calculate local noon.)

Should be enough info to hold down any future discussions to a minimum.

73  John  W0UN

Here's another addition, for those in sunny climes:

Drive a stake into the ground.  Observe how the shadow moves through 
the day.  Trace the path of the shadow's tip.  It should form a 
parabola, or similar (I can't remember which conic section it is, 
OK?).

The point at which the curve comes closest to the stake corresponds 
to local noon, and is due north of the stake.

Foolproof, and an excellent excuse for taking a day off and watching 
the shadow move.

Incidentally, you can obviously also use the tower itself to generate 
the shadow.

Chris R. Burger
ZS6EZ





Place a stake in the ground. Find the sun rise and sun set time for
that day. Devide it in half. The shadow from that stake at that time
will be true north. Compare it with the compus and you will see the
degrees difference.

John

Yes, Mick.  Just add/subtract the declination listed
on the topographical map for your area.  Any
rock-climbing or camping store should have
the maps. 

You need one of these maps anyway to do terrain
modeling for your antennas. (Download YT/YTAD
from ARRL).

Tom

I have read with interest the several postings concerning
ascertainment of true north.  I myself use a method different
from those described so far.

My method of indexing rotators, masts, and rotatable antennas to
compass headings does not depend upon a determination of 
true north and, therefore, avoids compasses, clocks, calculations, 
sun shadows, and the like.

I simply use a landmark of known (and constant) azimuth, and orient 
my antennas on the mast by sighting them against the landmark.  Works
wonderfully at the top of the tower, can be used on cloudy days, can
be used at any time during daylight hours, and is fabulously accurate.

In my own situation, a volcanic butte is visible near the
horizon from the top of my tower.  I obtained USGS 7.5 minute quadrangle 
maps that cover my QTH and the butte.  (It takes two maps for me
because the butte in question is on the quadrangle east of the one that
contains my QTH.)

An examination of the maps reveals that the butte is very nearly due east
of my QTH.  I calibrate the rotator indicator as described in the manual,
and then set the rotator exactly at north.  I then climb the tower and 
sight along the antenna element nearest the mast.  With the boom-to-mast
bracket somewhat loosened, I rotate the antenna on the mast until the 
element points straight at the butte.  (With a yagi, of course, I
position the antenna so that the reflector element is on the south side
of the mast.)  

Tighten the boom-to-mast clamp.  Perfect azimuth alignment automatically.

This method is easiest to use if one can find a landmark at one of the
principal compass points:  N E S or W.  A building, another tower,
a geological feature, or anything else that is visible, and the
location of which can be identified on the map, will work FB.

Bob, K0KR and K7KU

There are many quick and dirty ways!

- Determine true South, and true north is exactly opposite...  (pardon my
plagiarism...)

- Use a compass, determining the declination ("offset") from a USGS
topographic map.

- From your local newspaper - or your PacketCluster Node - determine your
local sunrise and sunset times.  Local noon is exactly halfway between
those two times.  The shadow cast by your tower or any other object
at local noon points at true north

- Locate Polaris (the North star).  The last two stars in the "dipper"
(not the handle) of the Big Dipper point at the north star.  The distance
between the last two start in the Big Dipper is about 1/5 the distance to
the north star.  Pardon my poor graphics, but this media has its limits...

                                        North
                                        Star
                                          ^
                                          |
                                          |
                                          |
                                          |
                                          |
                          X               |
                            
                 X              X         X 

                      

           X                    X         X


      X



73!
Frank
W3LPL
donovanf@sgate.com