Common Questions

Can I use a bigger antenna with more gain?

Can I use an amplifier?

Can I have 5 sites at 2 Mbps to a single 11 Mbps center site for better throughput?

Can I use a splitter and two antennas?

Can I double my distance with a repeater?

© 2003, Cisco Systems, Inc. All rights reserved. AWLF v3.1—4-60

Listed in the slide are the most common questions when it comes to obtaining more coverage distance. The answers require a small explanation of the advantages or drawbacks of each.

Is 50 dBi even better??

© 2003, Cisco Systems, Inc. All rights reserved. AWLF v3.1—4-61

Is 50 dBi even better??

© 2003, Cisco Systems, Inc. All rights reserved. AWLF v3.1—4-61

In Point-to-Multipoint systems, the FCC has limited the maximum EIRP (effective radiated power) in the 900 MHz, 2.4 GHz and 5.7 GHz spread spectrum bands to 36 dBm.

EIRP = transmit power + antenna gain.

At 2.4 GHz, Cisco Aironet's transmitter power is 20 dBm, so the largest antenna gain allowable is 16 dBi.

Under the "Professional Installer" clause, a trained installer may attach antennas with higher gain, if it is verified that the system is operating within the FCC rules and guidelines, but only if:

■ Antenna gain + transmitter power + cable losses is greater than or equal to 36 dBm.

■ In Point-to-Point system for 2.4 GHz system, using directional antennas the rules are changed. It has a 3:1 ratio for additional antenna gain (over 6 dBi) compared to TX power reduction.

■ At 30 dBm TX power, a 6-dBi antenna is still the max.

■ At 27 dBm TX power, (-3 dB) the antenna can be 9 dB above the initial 6, or 15 dBi.

■ At 24 dBm TX power, it would be possible to use a 24 dBi antenna.

Amplifiers?

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