Cisco Cisco VN 2900 Network Adaptation Interface Guía De Instalación

Because antennas transmit and receive radio signals, their performance can be adversely affected by the 
surrounding environment including distance between access point and client, physical obstructions, or 
radio frequency (RF) interference. 

Follow these guidelines to ensure the best possible performance: 

Wherever possible, mount the AP HWIC and antenna where the wireless devices would be within 
sight and avoid physical obstructions. Barriers along the line of sight between client and access point 
will degrade the wireless radio signals. AP HWICs and antennas can be installed above floor level 
in office environments or near the ceiling for better performance since most obstructions tend to be 
near floor level. 

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

Paper and vinyl walls have very little effect on signal penetration. 

Solid and precast concrete walls limit signal penetration to one or two walls without degrading 
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 or wire-mesh stucco walls causes signals to reflect back and cause poor 
penetration. 

Avoid mounting the antenna next to a column or vertical support that could create a shadow zone 
and reduce the coverage area. 

Keep the antenna away from reflective metal objects such as heating and air-conditioning ducts, 
large ceiling trusses, building superstructures, and major power cabling runs. If necessary, use an 
extension cable to relocate the antenna away from these obstructions. 

Install the AP HWIC and any antennas away from appliances that share the same frequency bands. 
Microwave ovens, cordless telephones, and security monitors can temporarily interfere with wireless 
performance. 

We recommend you avoid installing wireless antennas in or near rack-mounted installations that include 
networking equipment and computer servers whose radiated noise emissions can severely degrade radio 
performance. 

If the desired installation site has a marginally acceptable level of radiated noise emissions, consider 
using a remote-mounted antenna, such as a wall-mount or ceiling-mount antenna, for better radio 
performance and coverage.