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Re: How to calibrate the azimuth angle?



Here is an amsat-bb post from Tom Clark, K3IO, formerly W3IWI, on 
this subject. Wonderfully detailed. Thank you Tom. I have removed the 
 From line since the original address from 12 years ago may not be 
accurate. ron w8gus
====
Date: Tue, 17 Jan 95 20:12:13 UTC
From: Tom Clark
To: amsat-bb@AMSAT.Org
Subject: North/South vs East/West

The recent thread of Magnetic vs. Geodetic north-south for the 
calibration of antenna azimuths has overlooked an even easier way to 
do the deed. The idea is not new -- I believe it is the way the 
ancient Egyptians had their Nubian slaves establish the orientation 
of the great pyramids to accuracies of about a half-degree. Instead 
of trying to establish a North/South line,
determine East/West instead!

Here is the recipe (with some footnotes):

1. Wait for the morning of a clear, sunny day.
2. Find a level, flat area.
3. Poke a 3-6 foot (1-2 meter) stick in the ground vertically (south 
of the flat area in the northern hemisphere or north in the southern 
hemisphere).
4. Several times during the day, mark the location of the tip of the 
shadow of the stick.
5. The points you just marked will be on a straight line which is 
nominally East/West. Drive stakes at the ends of the line (or if your 
shadow is on concrete, paint the line).

Footnotes:

a. The accuracy of the east/west line is best at the solstices 
(Dec.21/Jun.21) and worst at the equinoxes (Mar.21/Sep.21). The sun's 
declination is a cosine curve with extrema of +/- 22.5 degrees 
reached at he solstices. At the equinoxes, the declination changes 
about 1/2 degree/day so if you are observing at the equinoxes over an 
8-hour period, the line will be in error by about 10 arc minutes.

b. The diameter of the sun's disk is about 30 arc minutes, so the 
shadow is "fuzzy" at this level. You need to be consistent in picking 
the point corresponding to the tip's shadow to minimize the penumbral 
error. The diameter of the stick should be big enough to give a solid 
shadow -- i.e. the stick should subtend an angle > 30 arc minutes 
when viewed from the level, flat area. I recommend that the stick 
have a length/diameter ratio of 20-30. A typical tall antenna tower 
will not cast a sharp enough shadow to use.

c. The level area need only be level in the east/west direction. A 
north/south slope will not affect the accuracy. If you don't have a 
level area, get a 4'x8' sheet of plywood and prop it with short 
stakes to make it level and cast the shadow onto the plywood. You 
should strive for east/west "levelness" of one degree or better if 
you want results good to about one degree.

Hope this idea helps -- 73 de Tom.

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