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[TowerTalk] Laying out antennas

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Subject: [TowerTalk] Laying out antennas
From: jimsmith@shaw.ca (Jim Smith)
Date: Thu, 27 Dec 2001 02:53:00 -0800
First off, my apologies for joining this thread so late.  I'm 1500
posts behind in my reading.

I'm puzzled that no one has posted what seems to me to be the
obvious solution although there have been oblique references to
it.  This usually means that I missed the point somehwere, but
anyway, here goes.

Because of trees and hills, sighting techniques are difficult as
it seems that one can't stand at one corner of the rectangle and
see anything at any other corner.

Linear measurements are difficult because of hills.

There is an alternative that is really easy, is completed faster
than any other way and should be within the required accuracy.

1.  Beg, borrow, rent or steal a hand held GPS unit which will do
averaging of position readings.  My old GPS II+ from Garmin will
do this.  The more channels it will receive the better this
averaging will be (well, anyway, it oughta be.  I don't actually
know.).  As I recall, my unit will receive 12 channels. Other
models of that vintage would receive only half that number. 
Anyway, when marking a position using averaging my unit claims to
be, typically, within 12 ft or so of being right.  The actual
claimed error depends on the positions of the satellites and how
many are in view.  What follows is based on my unit as I have no
experience with any other.

2.  Take the GPS unit, stand at the spot where you want one corner
of the rectangle to be and record the position on the GPS using
averaging, i.e. create a waypoint.  While you're there, drive a
stick into the ground.

3.  Calculate the lat and long of the other 3 corners of your
rectangle from a knowledge of which way you want the array to
point and how far apart one corner is supposed to be from the next
one.  How do you do this?  I don't remember but there must be many
places on the web that will tell you how.  The distances are so
small that I can't imagine that you would have to use spherical
trig.  As I recall, one minute of latitude or longitude is 1
nautical mile or 6080 ft.  If I'm wrong, I hope someone will
correct me.

4.  Get out the GPS again and create 3 new waypoints using the
lats and longs of the 3 corners you just calculated.  My unit will
allow you to enter lat or long to the nearest .001 minute which
would appear to translate to 6 ft.

5.  Set the GPS to go to one of the waypoints.  Go to the waypoint
and drive in a stick.

6.  Repeat for the other 2 corners.

7.  You're done.

How to decide whether to believe the GPS.

Surveyors have created a system of benchmarks (or are they called
monuments, I forget) where there are markers on the ground of
known lat and long.  Find out from the local gov't office where a
few of these are and what their coordinates are.  Take the GPS
there and see what it says.  Calculate how many feet the error is
and decide whether or not you are comfortable with the result.

I understand that there are surveyors' GPS units which are more
accurate.  If the consumer grade GPS isn't good enough, perhaps
you could rent one of these.

Please excuse the somewhat didactic style.  I used to be an
academic.

Hope this helps, Tom.  Lord knows, you've helped a lot of us.

73 & Happy New Year de Jim Smith        VE7FO

AN Wireless Self Supporting Towers are now available!  Windloading tables,
foundation diagrams and charts, along with full details are now at the
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