User's Manual

10271450001 Revision D 4–8 Installing ODUs Hub installation
Magnetic declination changes over time, so use only current
declination values.
A compass on a roof may be unreliable, due to metal
reinforcing rods in concrete and other metal. Stay away
from metal if possible. Take several readings. If readings
are not consistent, take readings on the street and mark true
north (accounting for declination) on the street where you
can see it from the roof. Use a compass only for
verification; do not rely on a compass alone to align the
antenna.
It may be helpful to mark true north, south, east, and west
on the roof using a chalked plumb line or some other
marking method.
Once you know true north (0°) you can easily determine
south, east, and west (at 90° intervals), as shown in figure
4-3. You can use the map, protractor, and landmarks to
determine any other direction (angle) on the map or with
respect to the actual site.
With true north, south, east, and west known, you can align
all HTs at the hub site. You could align them on the basis of
true north alone, but knowing the other three directions is
useful for reference and verification.
7. Use the map and landmarks to verify the directions you
have determined.
8. Place the protractor on the map, with its 0° (zero degree)
mark on true north. Then determine and plot the angle(s)
that corresponds to the HT alignment direction(s).