Antenna Installation
Overview

An antenna should be mounted to fully utilize its propagation characteristics. One way to do this is to orient the antenna horizontally, as high as possible, at or near the center of its coverage area. Figure lists the common antenna mounts.

Keep the antenna away from metal obstructions, such as heating and air-conditioning ducts, large ceiling trusses, building superstructures, and major power cabling runs. If necessary, use a rigid conduit, to lower the antenna away from these obstructions.

The density of the materials used in the construction of a building determines the number of walls the signal can pass through and still maintain adequate coverage. Consider the following before choosing the location to install an antenna:

  • Paper and vinyl walls have very little effect on signal penetration.
  • Solid and pre-cast concrete walls limit signal penetration to one or two walls without degraded coverage.
  • Concrete and wood block walls limit signal penetration to three or four walls.
  • A signal can penetrate five or six walls constructed of drywall or wood.
  • A thick metal wall causes signals to reflect, which causes poor penetration.
  • A chain link fence or wire mesh spaced between 2.5 and 3.8 cm (1 and 1.5 in.) acts as a harmonic reflector, which blocks a 2.4-Ghz radio signal.
  • Install the antenna away from microwave ovens and 2.4-GHz cordless phones. These products can cause signal interference, because they operate in the same frequency range.
  • Install the antenna horizontally to maximize signal propagation.

Every AP has an antenna attached to it. Most antennas are either shipped with a mounting bracket, or a mounting bracket is available as an option. The challenge is that most antennas are designed for mounting in a certain way.

A 5.2 dBi Mast-Mount Antenna is designed to be mounted on a mast and is shipped with the necessary hardware to mount it. To mount the antenna to an I-beam, creativity is needed. Standoff brackets are available, but these are not designed for mounting to an I-beam either. Some installers use zip ties, beam clamps, or bolts to attach the standoff brackets to I-beams. The antenna is then mounted to the bracket. When using a mast-mount antenna indoors, make sure it is mounted as shown in Figures and . The antenna is intended for outdoor use and is designed for mounting with the metal sleeve on the bottom. For indoor use, invert the antenna. Be creative. Modified brackets can be used for a variety of antennas.

Restrictions
When dealing with tall structures and tower installations, the codes and laws of each city or municipality may vary. A building permit to install towers or masts may be required, depending upon the height. The best of plans may fail if the building permits are not approved. Figure provides a step-by-step flow chart for installing an antenna. Figure illustrates antenna tower mounts.


Interactive Media Activity

Interactive Activity: Line of Sight of an Antenna

This activity helps demonstrate the Fresnel Zone between wireless bridges, and shows the effect of the curvature of the Earth on antennas.

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