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Cisco IOS Software Configuration Guide for Cisco Aironet Access Points
OL-30644-01
Chapter6 Configuring Radio Settings
Configuring Transmit and Receive Antennas
•Long—Long preambles are used by legacy 802.11 only devices, and some 802.11b/g devices that
expect long preambles for optimal operations. If these client devices do not associate to the wireless
devices, you should use short preambles.
You cannot configure short or long radio preambles on the 5-GHz radio.
Beginning in privileged EXEC mode, follow these steps to disable short radio preambles:
Short preambles are enabled by default. Use the preamble-short command to enable short preambles if
they are disabled.
Configuring Transmit and Receive Antennas
You can select the antenna the wireless device uses to receive and transmit data. There are three options
for both the receive and the transmit antenna:
•Gain—Sets the resultant antenna gain in dB.
•Diversity—This default setting tells the wireless device to use the antenna that receives the best
signal. If the wireless device has two fixed (non-removable) antennas, you should use this setting
for both receive and transmit. If the device has three removable antennas, you can use this setting to
have all of them operate in diversity mode
•Right—If the wireless device has removable antennas and you install a high-gain antenna on the
wireless device's right connector, you should use this setting for both receive and transmit. When
you look at the wireless device's back panel, the right antenna is on the right.
•Middle—If the wireless device has removable antennas and you install a high-gain antenna on the
wireless device middle connector, you should use this setting for receiving only. The antennas
available for transmitting in a three-antenna configuration are the right and left antennas.
•Left—If the wireless device has removable antennas and you install a high-gain antenna on the
wireless device's left connector, you should use this setting for both receive and transmit. When you
look at the wireless device's back panel, the left antenna is on the left.
This does not apply for dual antenna APs such as the 1600, 2600, and 3600 series. Please check the
respective hardware guides for further information.
Command Purpose
Step1 configure terminal Enter global configuration mode.
Step2 interface dot11radio { 0slot/port } Enter interface configuration mode for the 2.4-GHz radio
interface.
Step3 no preamble-short Disable short preambles and enable long preambles.
Step4 end Return to privileged EXEC mode.
Step5 copy running-config startup-config (Optional) Save your entries in the configuration file.