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Safety Guidelines and Warnings
Avoiding Damage to Radios in a Testing Environment
The radios on outdoor units (bridges) have higher transmit power levels than radios on indoor units (APs).
When you test high-power radios in a link, you must avoid exceeding the receiver's maximum receive input
level. At levels above the normal operating range, packet error rate (PER) performance is degraded. At even
higher levels, the receiver can be permanently damaged. To avoid receiver damage and PER degradation, you
can use one of the following techniques:
• Separate the omnidirectional antennas by at least 2 ft (0.6 m) to avoid receiver damage or by at least 25
Note
• Reduce the configured transmit power to the minimum level.
For a radiated testbed, the following equation describes the relationships among transmit power, antenna gain,
attenuation, and receiver sensitivity:
txpwr + tx gain + rx gain - [attenuation due to antenna spacing] < max rx input level
Where:
txpwr = Radio transmit power level
tx gain = transmitter antenna gain
rx gain = receiver antenna gain
Performing Site Surveys
Every network application is a unique installation. Before installing multiple APs, you should perform a site
survey to determine the optimum use of networking components and maximize range, coverage, and network
performance.
Site surveys reveal problems that can be resolved before the network is operational. Because 802.11a/b/g/n/ac/ax
operates in an unlicensed spectrum, there may be sources of interference from other 802.11a wireless devices
(especially in multi-tenant buildings) that could degrade your 802.11 signals. A site survey can determine if
such interference exists at the time of deployment.
Consider the following operating and environmental conditions when performing a site survey:
• Data rates: Sensitivity and range are inversely proportional to data bit rates. The maximum radio range
• Antenna type and placement: Proper antenna configuration is a critical factor in maximizing radio range.
• Physical environment: Clear or open areas provide better radio range than closed or filled areas.
ft (7.6 m) to avoid PER degradation.
These distances assume free space path loss and are conservative estimates.
Required separation distances for damage and performance degradation levels
in actual deployments are less if conditions are not non-line-of-sight.
is achieved at the lowest workable data rate. A decrease in receiver sensitivity occurs as the radio data
increases.
As a general rule, range increases in proportion to antenna height. However, do not place the antenna
higher than necessary because the extra height also increases potential interference from other unlicensed
radio systems and decreases the wireless coverage from the ground.
Cisco Catalyst IW9167I Heavy Duty Access Point Hardware Installation Guide
Avoiding Damage to Radios in a Testing Environment
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