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
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