Antennas
Variables

Antenna maximum distances are usually expressed in kilometers or meters. Determining the maximum distance between the antennas at each end of a link is not a simple problem to solve. The maximum link distance is governed by all of the following:

  • Maximum available transmit power
  • Receiver sensitivity
  • Availability of an unobstructed path for the radio signal
  • Maximum available gain, for the antenna(s)
  • System losses (such as loss through coax cable runs, connectors, and so on)
  • Desired reliability level (availability) of the link

Some product literature or application tables will quote a distance. In general, this distance value is optimum, with all variables that are listed in Figure optimized. Also, the availability requirement will have a drastic affect on the maximum range. A link distance can exceed standard distances, if consistently higher error rates are acceptable.

The best way to know the functional distance, between WLAN devices, is to do a good site survey. A site survey involves examination, at each proposed link location. An examination of the terrain and man-made obstructions will help determine the feasibility of the site. For outdoor bridging site surveys, it can also help determine possible tower needs. The result of such a survey will yield the following information:

  • The radio path loss
  • Any issues that may further compromise link performance, such as potential interference

Once the site survey is done, calculations and equipment choices need to be made. Variables such as antenna gain and type, as listed in Figure , will lead to a definitive answer for the maximum range.