Hewlett Packard Enterprise Company AP175 Manual Do Utilizador
6
Aruba AP-175 Outdoor Access Point
| Installation Guide
radio signal power travels. This area is known as the first Fresnel Zone of the radio link. For a radio link, no
object (including the ground) must intrude within 60% of the first Fresnel Zone.
object (including the ground) must intrude within 60% of the first Fresnel Zone.
Figure 3
illustrates the concept of a good radio line of sight.
Figure 3 Line of Sight
If there are obstacles in the radio path, there may still be a radio link but the quality and strength of the
signal will be affected. Calculating the maximum clearance from objects on a path is important as it directly
affects the decision on antenna placement and height. It is especially critical for long-distance links, where
the radio signal could easily be lost.
signal will be affected. Calculating the maximum clearance from objects on a path is important as it directly
affects the decision on antenna placement and height. It is especially critical for long-distance links, where
the radio signal could easily be lost.
When planning the radio path for a wireless bridge or mesh link, consider these factors:
z
Avoid any partial line of sight between the antennas
z
Be cautious of trees or other foliage that may be near the path, or may grow and obstruct the path.
z
Be sure there is enough clearance from buildings and that no building construction may eventually block
the path.
the path.
z
For very long distance links, the curvature of the earth (20 cm per km) may need to be considered in the
calculation of relative heights.
calculation of relative heights.
z
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)
satellite image data (software packages are available that may include this information for your area)
z
Avoid a path that may incur temporary blockage due to the movement of cars, trains, or aircraft.
Antenna Height
A reliable wireless bridge or mesh link is usually best achieved by mounting the antennas at each end 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).
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, the AP may have to be mounted on masts or poles that are tall enough to attain the
minimum required clearance. Use the following table to estimate the required minimum clearance above
the ground or path obstruction (for 5 GHz bridge links).
minimum required clearance. Use the following table to estimate the required minimum clearance above
the ground or path obstruction (for 5 GHz bridge links).
Table 3 Antenna Minimum Height and Clearance Requirements
Total Link Distance
Max Clearance for
60% of First Fresnel
Zone at 5.8 GHz
60% of First Fresnel
Zone at 5.8 GHz
Approximate Clearance
for Earth Curvature
for Earth Curvature
Total Clearance
Required at
Mid-point of Link
Required at
Mid-point of Link
0.25 mile (0.402 km)
4.6 ft (1.4 m)
0.007 ft (0.002 m)
4.6 ft (1.4 m)
0.5 mile (0.805 km)
6.2 ft (1.9 m)
0.03 ft (0.010 m)
6.2 ft (1.9 m)
Radio Line of Sight
Visual Line of Sight
AP-175-IG-Rev01.fm Page 6 Friday, September 17, 2010 4:27 PM