Table of Contents
Advertisement
If there is any obstacle in the radio path, it may still be a radio link but the quality and the signal strength
will be affected. Ensuring the maximum clearance from objects on a path is important to locate the
antennas and the height. For the long-distance links, the radio signals might be lost partially due to the
non-LOS issue.
As we setup the radio path for the wireless bridge link, it needs to consider these factors:
any building or construction blocking the path.
maps, aerial photos, or even satellite image data.
moving objects, such as cars, trains, or aircrafts.
Note: For the wireless link less than 500 m, the IEEE 802.11a radio signal will tolerate some obstacles in
the path and may not even require a visual line of sight between the antennas.
5.3.1 Antenna Height
The reliable wireless linkage usually depends on the both sides' antennas for a clear radio line of
sight. The minimum height is up to the link distance, obstacles that may be in the path, topology of
the terrain, and the curvature of the earth (for links over 2 miles). For the long-distance links, the
mast or the pole may need to be constructed to attain the minimum required height. The following
table is for you to estimate the required minimum clearance above the ground or path obstruction.
Total link distance Max clearance for 60% of
first Fresnel zone at 5.8GHz
0.25 mile (402 m)
4.5 ft (1.4 m)
0.5 mile (805 m)
6.4 ft (1.95 m)
1 mile (1.6 km)
9 ft (2.7 m)
Avoid any partial line-of-sight between the antennas.
Be aware of trees that may be near the path or obstruct the path.
Make sure there is enough clearance from buildings and there is no
Check the land topology between the antennas using topographical
Avoid a path that may have the temporary blockage due to the
Approximate clearance
for earth curvature
0
0
0
- 23 -
Total clearance required at
mid-point of link
4.5 ft (1.4 m)
6.4 ft (1.95 m)
9 ft (2.7 m)
Advertisement
Table of Contents
