Personally, I've always had bad luck with Broadcom chipsets (e.g. flaky connection, into & out of monitor mode, etc), and therefore stay away from them. It may be easier to simply purchase a more compatible wi-fi card (several good ones are recommended on the hardware compatibility list forums, as well as the Wi-Fu course at Offensive Security).


Be sure to run airmon-ng to see if your card will go into monitor mode, and aireplay-ng to do an injection test.
