Cambium Networks PTP 550 Series, User Manual

Page: 61 / 249

Chapter 3: System planning Site planning
Page 3-23
ODU and external antenna location
Find a location for the ODU (and external antenna for connectorized units) that meets the
following requirements:
•
The equipment is high enough to achieve the best radio path.
•
People can be kept a safe distance away from the equipment when it is radiating. The safe
separation distances are defined in
Calculated distances on page 4-65 .
•
The equipment is lower than the top of the supporting structure (tower, mast or building)
or its lightning air terminal.
•
If the ODU is connectorized, select a mounting position that gives it maximum protection
from the elements, but still allows easy access for connecting and weatherproofing the
cables. To minimize cable losses, select a position where the antenna cable lengths can be
minimized. If diverse or two external antennas are being deployed, it is not necessary to
mount the ODU at the midpoint of the antennas.
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 PTP 550 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 will subject the mounting structure to significant lateral force. The
magnitude of the force depends on both wind strength and surface area of the ODU. Wind
loading is estimated using the following formulae:
•
Force (in newtons) = 0.5 × ρ × V 2 × A × C
d
o
“ ρ ” is the density of air = 1.225 kg/m 3 ,
o
“V” is the wind speed in meters per second,
o
“A” is the projected surface area of the ODU in square meters, and
o
“C
d
” is the drag coefficient = 1.385.
The drag coefficient has been measured when the cover plate or antenna is perpendicular to
the air flow.
Applying these formulae to the PTP 550 ODU at different wind speeds, the resulting wind
loadings are shown in
Table 29 .
Table 21 ODU wind loading (newtons)
Type of ODU Max surface
area (square
meters) Wind speed (kilometers per hour)
225
250 275 300 325
Integrated (23 dBi) 0.130 308 N 380 N 460 N 547 N 643 N
Connectorized 0.051 169 N 208 N 253 N 300 N 353 N
Equivalent results in US customary units are shown in Table 30 .