Quidway WB2011, Руководство пользователя

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Bridge Link Planning
2-4
2
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.
A wireless bridge link is deployed to connect building A to 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
(7.5 ft) mast or pole must be contructed on its roof to achieve the required antenna
height. Building B is only three stories high, or 9 m (30 ft), but is located at an
elevation that is 12 m (39 ft) higher than bulding A. To mount an anntena at the
required height on building B, a mast or pole of only 1.3 m (4.3 ft) is needed.
Warning: Never construct a radio mast, pole, or tower near overhead power lines.
Note: Local regulations may limit or prevent construction of a high radio mast or tower. If
your wireless bridge link requires a high radio mast or tower, consult a
professional contractor for advice.
Antenna Position and Orientation
Once the required antenna height has been determined, other factors affecting the
precise position of the wireless bridge must be considered:
• Be sure there are no other radio antennas within 2 m (6 ft) of the wireless bridge
• Place the wireless bridge away from power and telephone lines
15 miles (24.1 km) 35 ft (10.7 m) 45 ft (13.7 m) 80 ft (24.4 m)
17 miles (27.4 km) 37 ft (11.3 m) 58 ft (17.7 m) 95 ft (29 m)
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
A
B
3 miles (4.8 km)
5.4 m
17 m
20 m
2.4 m
12 m
9 m
1.4 m
Visual Line of Sight
Radio Line of Sight