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

-- AmitaEkbote - 12 Mar 2010