3Com WL-575, 3CRWEASYA73 manual Radio Path Planning

RADIO PATH PLANNING

Although the wireless bridge uses IEEE 802.11a radio technology, which is capable of reducing the effect of multipath signals due to obstructions, the wireless bridge link requires a “radio line-of-sight” between the two antennas for optimum performance.

The concept of radio line-of-sight involves the area along a radio link path through which the bulk of the radio signal power travels. This area is known as the first Fresnel Zone of the radio link. For a radio link not to be affected by obstacles along its path, no object, including the ground, must intrude within 60% of the first Fresnel Zone.

The following figure illustrates the concept of a good radio line-of-sight.

Visual Line of Sight Radio 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.

When planning the radio path for a wireless bridge link, consider these factors:

•Avoid any partial line-of-sight between the antennas.

•Be cautious of trees or other foliage that may be near the path, or may grow and obstruct the path.

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