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Poor bridge performance due to the improper alignment of the antenna


Core Issue

Wireless bridges can have intermittent connectivity losses and poor throughput if the RF antennas are not correctly aligned.


Antenna alignment directly relates to the proper Line of Sight (LoS) between the two wireless bridges. When the antennas are properly aligned, the Radio Frequency (RF) LoS between the devices is clear, and connectivity problems do not occur.

Antenna alignment for directional antennas is very important. Since directional antennas are used to communicate between two bridges, align the antennas manually for proper bridge operation. Directional antennas have greatly reduced radiation angles. The radiation angle for yagi antennas is approximately 25 to 30 degrees. For parabolic dish antennas, the radiation angle is approximately 12.5 degrees. To ensure proper antenna alignment between wireless bridges, follow the guidelines given in the Basic Antenna Alignment section of Antenna Basics.

The bridge link test helps measure the alignment of two antennas after the bridges are associated. The association indicates the antennas point in the general vicinity of each other, but does not indicate that the antennas are properly aligned. The link test provides information used to gauge the alignment. For information on how to perform the link test, refer to the Performing a Link Test section of Antenna Basics.

Also, use the Cisco Outdoor Bridge Range Calculation Utility to calculate the range of the antenna. The Cisco Outdoor Bridge Range Calculation Utility is the best tool to calculate the Fresnel zone, the distance between bridges, cable loss, required antenna height. For more information on this, refer to the Outdoor Bridge Range Calculation Utility.

For information on how to align the integrated antennas on a 1300 Wireless Bridge, refer to the Aligning the Bridge Antenna Using RSSI LED Indications section of the Mounting and Alignment Overview.

For information on the different types of antenna and their specifications, refer to the Cisco Aironet Antenna Reference Guide. Use the information provided in this document to choose the correct antenna for the situation.

Problem Type

Poor connectivity / Performance

Intermittent connectivity - flapping



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