3Com WL-575, 3CRWEASYA73 manual Miles 4.8 km 20 m 17 m 12 m

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 Radio Line of Sight

3 miles (4.8 km)

2.4m

20 m

A

5.4 m

17 m

B		1.4 m
		9 m
	12 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 buildings 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 constructed 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 building A. To mount an antenna 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.

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