User guide

Radio Path Planning
2-3
2
When planning the radio path for a wireless bridge link, consider these factors:
• Avoid any partial line-of-sight between the antennas.
• Be cautious of trees or other foliage that may be near the path, or may grow and
obstruct the path.
• Be sure there is enough clearance from buildings and that no building construction
may eventually block the path.
• Check the topology of the land between the antennas using topographical maps,
aerial photos, or even satellite image data (software packages are available that
may include this information for your area)
• Avoid a path that may incur temporary blockage due to the movement of cars,
trains, or aircraft.
Antenna Height
A reliable wireless link is usually best achieved by mounting the antennas at each
end just high enough for a clear radio line of sight between them. The minimum
height required depends on the distance of the link, obstacles that may be in the
path, topology of the terrain, and the curvature of the earth (for links over 3 miles).
For long-distance links, a mast or pole may need to be contsructed to attain the
minimum required height. Use the following table to estimate the required minimum
clearance above the ground or path obstruction.
.
Total Link Distance Max Clearance for
60% of First Fresnel
Zone at 5.8 GHz
Approximate
Clearance for
Earth Curvature
Total Clearance
Required at
Mid-point of Link
0.25 mile (402 m) 4.5 ft (1.4 m) 0 4.5 ft (1.4 m)
0.5 mile (805 m) 6.4 ft (1.95 m) 0 6.4 ft (1.95 m)
1 mile (1.6 km) 9 ft (2.7 m) 0 9 ft (2.7 m)
2 miles (3.2 km) 12.7 ft (3.9 m) 0 12.7 ft (3.9 m)
3 miles (4.8 km) 15.6 ft (4.8 m) 1.8 ft (0.5 m) 17.4 ft (5.3 m)
4 miles (6.4 km) 18 ft (5.5 m) 3.2 ft (1.0 m) 21.2 ft (6.5 m)
5 miles (8 km) 20 ft (6.1 m) 5 ft (1.5 m) 25 ft (7.6 m)
7 miles (11.3 km) 24 ft (7.3 m) 9.8 ft (3.0 m) 33.8 ft (10.3 m)
9 miles (14.5 km) 27 ft (8.2 m) 16 ft (4.9 m) 43 ft (13.1 m)
12 miles (19.3 km) 31 ft (9.5 m) 29 ft (8.8 m) 60 ft (18.3 m)