D-Link ANT24-1800 User Guide - Page 27
System Requirements
UPC - 790069239946
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FSyrsetsemneRl eZqounireements Line-of-Sight (LOS) Visual and RF Line-of-Sight ( LOS ) between the sending and receiving antennas is essential in achieving long range in wireless communication systems. There are two types of LOS that are generally used to describe an environment: Visual LOS is the ability to see from one site to the other. It requires only a straight liner path between two points. RF LOS requires not only visual LOS, but also a football-shaped path free of obstacles for data to optimally travel from one point to another. Fresnel Zone: The Fresnel Zone can be thought of as a football-shaped tunnel between two sites that provides a path for RF signals. In order to achieve the greatest range, the football-shaped path in which radio waves travel must be free of obstructions. Buildings, trees or any other obstacles in the path will decrease the communication range. If the antennas are mounted just barely off the ground, over half of the Fresnel zone ends up being obstructed by the earth resulting in significant reduction in range. To avoid this problem, the antenna should be mounted high enough off of the ground so that the earth does not interfere with the central radius of the Fresnel zone. 27