Unanswered Question
May 20th, 2010


We have several of these wireless access points thru out our building and am wondering about antena placement on thse devices.  Several space the antena about a foot and a half appart, some are at a double arms stretch.  We've "inhereted" these devices and people complain ther eare "dead Zones" and we're trying to fix.

What is optimum?  Is there a "Users" manual that I can access/download for these devices??



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I have this problem too.
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rob.huffman Fri, 05/21/2010 - 06:39

Hi Tom,

In a multipath environment, signal null points are located throughout  the area. The distance an RF wave travels, how it bounces, and where  the multipath null occurs are based on the wavelength of the frequency.  As frequency changes, so does the length of the wave. Therefore, as  frequency changes, so does the location of the multipath null. The  length of the 2.4 GHz wave is approximately 4.92 inches (12.5 cm). The  length of the 5 GHz wave is approximately 2.36 inches (6 cm).

In order to  increase coverage, conduct a site survey to determine the RF coverage of  the antennas. Place access points in the appropriate areas of the  installation site. The purpose of diversity is to overcome multipath  reflections. Diversity antennas that share the same physical housing are  placed at an optimum distance apart. The maker of the particular  antenna determines that distance based on the characteristics of the  antenna. When you use a pair of antennas with matching characteristics  to provide diversity for cell coverage in your facility, the guideline  is to put those matched antennas at a distance apart from each other  that is equal to a multiple of the wavelength of the frequency that is  being transmitted. The 2.4 GHz wavelength is approximately 4.92 inches.  Therefore, to support diversity on a 2.4 GHz radio with two separate  antennas, the antennas should be spaced approximately 5 inches apart.  The antenna pair could also be spaced at multiples of 5 inches, but the  distance between should not exceed 4 multiples: reflected waves farther  apart than that are likely to be so distorted and different in delay  spread that the radio could not work with them.Because each antenna is  selected by itself, both antennas must have the same radiation  characteristics and be positioned to provide similar cell coverage. Two  antennas connected to the same access point must not be used to cover  two different cells.

From this good doc;

Multipath and Diversity

Hope this  helps!


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