[amsat-bb] Compass difficulties, was Re: How to calibrate the azimuth angle?
joe cassano aka jmario
jmario at fast.net
Thu Dec 27 23:06:09 PST 2007
I am kind of surprised at the number of "compass is hard to use"
comments here. I use a compass and a Home Depot angle locater to set
the azimuth and elevation of a 220 yagi that I have mounted on an old
Atlas studio boom microphone stand in by back yard to capture the
passage of the moon through the SPASUR (Lake Kickapoo) radio fence. I
usually try to do the antenna pointing during daylight hours. It is a
lot easier to read the compass while sighting along the boom in
daylight. Whenever I check my alignment by sighting along the antenna
boom when the moon is passing through the fence (i.e. moon is at azimuth
of 91.4 or 271.4 degrees relative to Lake Kickapoo and the moon is
above the horizon at both Lake Kickapoo and my QTH in Pennsylvania) I
find I've got the moon boresighted.
It is a given that you keep the compass away from ferrous objects while
taking a reading - that includes non-obvious objects like the wrench or
pliers in your back pocket that you might have forgot about :-)
Alternatively, if you are going to be climbing a tower or some such
thing, you can always calibrate the azimuth angle (that was the original
question) by determining the bearing of a distant object then pointing
the antenna at that same distant object.
The unmentioned question in the original post is just how accurate does
the azimuth angle calibration need to be? The above mentioned 220 yagi
is (if I remember correctly) 3db down at +/- 15 degrees so az angle is
not critical but a hi gain EME array might have a 3db width of +/- 2
degrees requiring more pointing/azimuth accuracy.
More information about the AMSAT-BB