Edimax RA21S User Manual page 88

Preamble Type
CTS Protection
Tx Power
Set the wireless radio preamble type. The
default value is "Short Preamble".
Enabling this setting will reduce the chance
of radio signal collisions between 802.11b
and 802.11g wireless access points. It's
recommended to set this option to "Auto".
Set the power output of the wireless radio.
You may not require 100% output power.
Setting a lower power output can enhance
security since potentially malicious/unknown
users in distant areas will not be able to
access your signal.
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