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If the clearance for your antenna installation is equal to or better than the minimum clearance required, then the Clearance
Factor for your installation is 100%. If your actual clearance is less than the minimum clearance, then refer the above figure to
determine the actual range that applies to the current requirement.
: Practically, it is impossible to achieve the maximum range due to the interference from the other radio products.
Proxim recommends you to maintain at least 60-70% of the first Fresnel Zone free. If the clearance is lower than this
percentage, then the link budget and acquired fade margin are affected. Clearances more than 100% of the Fresnel Zone can
cause reflections that are 180 degrees out of phase and can cancel the signal. The Fresnel Zone works in both the horizontal
and vertical paths.
9.5 Calculations
A microwave link is established along the path between antennas. Availability of the microwave path is therefore a prediction
of the percent of time that the wireless link operates. In the absence of direct interference, availability of microwave path is
affected by the following factors:
•
Path length
•
Fade margin
•
Frequency
•
Terrain (smooth, average, mountainous)
•
Climate (dry, temperate, humid)
Availability of the microwave path can be improved by increasing the fade margin, either by making the path shorter or by
using the higher gain antennas in conjunction with lower loss antenna cable (using a higher quality antenna cable, shortening
the length, or both).
Establish a wireless link for a specific availability rate of microwave path, depending upon the type of information carried over
the link and the overall network design redundancy. Let's say, the data or voice traffic carried by the radio is critical, then the
link can be established at a very high availability rate of microwave path (say, 99.999% or 5.3 minutes of predicted outage
per year).
9.5.1 Calculating Link Budget
Use the following formula to estimate the received signal level (RSL):
RSL (dBm) = P
- L
out
1
®
ORiNOCO
AP-9200R - Hardware Installation Guide
Figure 9-3 Clearance Factor
+ G
+ G
- L
- L
1
2
2
p
Measuring Signal Performance
56
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