3Com 3CRWEASYA73 quick start Aligning Antennas, Rssi

8 Aligning Antennas

After wireless bridge units have been mounted, connected, and their radios are operating, bridge link antennas must be accurately aligned to ensure optimum performance. This alignment process is particularly important for long-range point-to-point links. In a point-to-multipoint configuration the root bridge uses an omnidirectional or sector antenna, which does not require alignment, but bridge nodes still need to be correctly aligned with the root bridge antenna.

•Point-to-Point Configurations – In a point-to-point configuration, the alignment process requires two people, one at each end of the link. The use of cell phones or two-way radio communication may help with coordination. To start, you can just point the antennas at each other, using binoculars or a compass to set the general direction. For accurate alignment, you must monitor the signal strength LEDs as the antenna moves horizontally and vertically.

•Point-to-Multipoint Configurations – In a point-to-multipoint configuration all bridge nodes must be aligned with the root bridge antenna. The alignment process is the same as in point-to-point links, but only the bridge node end of the link requires the alignment.

The signal strength LEDs indicate the received radio signal strength for a particular bridge link. The more LEDs that turn on, the stronger the signal. Alternatively, you can monitor the Receive Signal Strength Indicator (RSSI) value directly from the management interface. The higher the RSSI value, the stronger the signal.

When you move the antenna during alignment, the radio signal from the remote antenna can be seen to have a strong central main lobe and smaller side lobes. The object of the alignment process is to set the antenna so that it is receiving the strongest signal from the central main lobe.

Vertical Scan

Remote

Antenna

Horizontal Scan

Main Lobe

	Maximum	RSSI Value
RSSI
Value		Side Lobe
		Maximum

Maximum Signal

Strength Position for

Vertical Alignment

Maximum Signal Strength Position

for Horizontal Alignment

To align the antennas in the link, monitor the signal strength LEDs or the RSSI value in the management interface. Start with one antenna fixed and then perform the following procedure on the other antenna:

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