System Planning 72
bar (TGB) if installed.
l If the tower is greater than 61 m (200 ft) in height, the drop cable shield must be grounded at the
tower midpoint, and at additional points as necessary to reduce the distance between ground
cables to 61 m (200 ft) or less.
l In high lightning-prone geographical areas, the drop cable shield must be grounded at the spacing
between 15 to 22 m (50 to 75 ft). This is especially important on towers taller than 45 m (150 ft).
For roof installations, use the following additional criteria:
l The drop cable shield must be bonded to the building grounding system at its top entry point
(usually on the roof).
l The drop cable shield must be bonded to the building grounding system at the entry point to the
equipment room.
ODU wind loading
Ensure that the ODU and the structure on which it is mounted are capable of withstanding the prevalent
wind speeds at a proposed site. Wind speed statistics should be available from national meteorological
offices.
The ODU and its mounting bracket are capable of withstanding wind speeds of up to 325 kph (200 mph).
Wind blowing on the ODU subjects the mounting structure to significant lateral force. The magnitude of
the force depends on both wind strength and the surface area of the ODU. Wind loading is estimated
using the following formulae:
l Force (in newtons) = 0.5 × ρ × V
2
× A × C
d
l “ρ” is the density of air ( 1.225 kg/m
3
)
l “V” is the wind speed in meters per second
l “A” is the projected surface area of the ODU in square meters
l “C
d
” is the drag coefficient = 1.385.
The drag co-efficient has been measured when the cover plate or antenna is perpendicular to the air flow.
Applying these formulae to the cnWave ODU at different wind speeds, the resulting wind loadings are
shown in the following ODU wind loading (newtons) table:
Table 28: ODU wind loading (newtons)
Type of ODU Max surface area (square meters) Wind speed (km/h Newtons)
200* 225 250 275 300 325
V1000 0.017544 44 56 69 83 99 116
V2000 0.0368 61 78 96 116 138 162
v3000** 0.1764 462 583 719 871 1036 1216
V5000 0.052597188 118 148 185 224 266 312
Equivalent results in US customary units are shown in following ODU wind loading (pounds force) table:
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