Alvarion BREEZENET RB-DS.11 - Manual (Page 21)

Installation
2-5
Outdoor Installation Considerations
This section describes various considerations to take into account when planning
an outdoor installation including site selection, antenna alignment, antenna
polarization, antenna seal, and cell size.
Collocating DS.11 Outdoor Units
Up to three BU-DS.11 units with omni-directional antennas (the exact number
depends on the number of non-overlapping channels available in the relevant
regulatory domain) can be collocated on the same building top or tower.
Collocating more than three units may decrease performance depending upon the
type of antenna and its direction. Each unit should be assigned to one of the non-
overlapping channels: 1, 7, or 13 in ETSI or 1, 6 or 11 in FCC.
The antennas of collocated units should be mounted at least 60 cm (2 feet) apart
when using UNI-16’s, 4.5 m (15 feet) apart when using UNI-24’s, and 21 m (75
feet) apart when using OMNI-8’s. Omni antennas must be separated also vertically.
Greater separation will improve the link distance.
Site Selection Factors
When selecting a location for outdoor units and external antennas, remember to
take into consideration the following guidelines:
♦ Minimum distance between sites.
♦ Maximum height above the ground.
♦ Maximum line of sight clearance.
Path of Clearest Propagation
A propagation path is the path that signals traverse between the antennas of any
two units. The “line” between two antenna sites is an imaginary straight line,
which may be drawn between the two antennas. Any obstacles in the path of the
“line” degrade the propagation path. The best propagation path is, therefore, a
clear line of sight with good clearance between the “line” and any physical obstacle.
Physical Obstacles
Any buildings or other physical structures such as trees, mountains or other
geographic features higher than the antenna and situated in the path between the
two sites can constitute obstructions and cause signal attenuation. Install outdoor
antennas high enough to avoid any obstacles that may block the signal.