Table of Contents
Advertisement
.
Total Link Distance
0.25 mile (402 m)
0.5 mile (805 m)
1 mile (1.6 km)
2 miles (3.2 km)
3 miles (4.8 km)
4 miles (6.4 km)
5 miles (8 km)
7 miles (11.3 km)
9 miles (14.5 km)
12 miles (19.3 km)
15 miles (24.1 km)
17 miles (27.4 km)
Note that to avoid any obstruction along the path, the height of the object must be
added to the minimum clearance required for a clear radio line-of-sight. Consider the
following simple example, illustrated in the figure below.
Visual Line of Sight
A
2.4 m
20 m
A wireless bridge link is deployed to connect building A to a building B, which is
located three miles (4.8 km) away. Mid-way between the two buidings is a small
tree-covered hill. From the above table it can be seen that for a three-mile link, the
object clearance required at the mid-point is 5.3 m (17.4 ft). The tree-tops on the hill
are at an elevation of 17 m (56 ft), so the antennas at each end of the link need to be
at least 22.3 m (73 ft) high. Building A is six stories high, or 20 m (66 ft), so a 2.3 m
Max Clearance for
60% of First Fresnel
Zone at 5.8 GHz
4.5 ft (1.4 m)
6.4 ft (1.95 m)
9 ft (2.7 m)
12.7 ft (3.9 m)
15.6 ft (4.8 m)
18 ft (5.5 m)
20 ft (6.1 m)
24 ft (7.3 m)
27 ft (8.2 m)
31 ft (9.5 m)
35 ft (10.7 m)
37 ft (11.3 m)
3 miles (4.8 km)
17 m
Approximate
Clearance for
Earth Curvature
0
0
0
0
1.8 ft (0.5 m)
3.2 ft (1.0 m)
5 ft (1.5 m)
9.8 ft (3.0 m)
16 ft (4.9 m)
29 ft (8.8 m)
45 ft (13.7 m)
58 ft (17.7 m)
Radio Line of Sight
5.4 m
Radio Path Planning
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)
12.7 ft (3.9 m)
17.4 ft (5.3 m)
21.2 ft (6.5 m)
25 ft (7.6 m)
33.8 ft (10.3 m)
43 ft (13.1 m)
60 ft (18.3 m)
80 ft (24.4 m)
95 ft (29 m)
B
1.4 m
9 m
12 m
3
3-3
Advertisement
Table of Contents
