Appendix D Wireless LANs
VMG1312-B Series User’s Guide
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2.5% . For an unobstruct ed outdoor site, each 1dB increase in gain result s in a range increase of
approximat ely 5% . Act ual results m ay vary depending on the network environm ent .
Antenna gain is som et im es specified in dBi, which is how m uch the antenna increases the signal
power com pared to using an isot ropic ant enna. An isot ropic antenna is a t heoretical perfect antenna
that sends out radio signals equally well in all direct ions. dBi represents t he t rue gain that the
ant enna provides.
Types of Antennas for WLAN
Ther e are t wo t ypes of ant ennas used for wireless LAN applications.
• Om ni- dir ectional antennas send t he RF signal out in all directions on a horizont al plane. The
coverage area is t orus- shaped ( like a donut ) which m akes these antennas ideal for a room
environm ent . With a wide coverage area, it is possible t o m ake circular overlapping coverage
areas with m ult iple access point s.
• Direct ional antennas concent rate the RF signal in a beam , like a flashlight does wit h t he light
from its bulb. The angle of t he beam det erm ines the widt h of the coverage patt ern. Angles
typically range from 20 degrees (very directional) t o 120 degrees (less direct ional) . Direct ional
ant ennas are ideal for hallways and outdoor point-t o- point applications.
Positioning Antennas
I n general, antennas should be m ounted as high as practically possible and free of obst ruct ions. I n
point- to–point application, posit ion both ant ennas at t he sam e height and in a direct line of sight to
each ot her to att ain t he best perform ance.
For om ni-directional ant ennas m ount ed on a t able, desk, and so on, point the antenna up. For
om ni- directional antennas m ount ed on a wall or ceiling, point the antenna down. For a single AP
applicat ion, place om ni- direct ional antennas as close to the center of the coverage area as possible.
For direct ional antennas, point the antenna in the direction of the desired coverage area.
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