Antenna diversity can cause a lot of problems especially while trying to set the tx power. To turn off antenna diversity and specify which one to use we use the following commands
sysctl -w dev.wifi0.diversity=0
sysctl -w dev.wifi0.txantenna = 1
sysctl -w dev.wifi0.rxantenna = 1
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AmitaEkbote - 12 Mar 2010