Can a Mac's airport card run 802.11 N, G, B or A only?

Solution 1:

Maybe this help, you can access to the airport command utility with

sudo ln -s /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport /usr/sbin/airport

Then, type

sudo airport en1 prefs JoinMode=Strongest JoinModeFallback=KeepLooking

JoinMode = Ranked and JoinModeFallback = Prompt are the defaults, if you want to switch back

Solution 2:

If you just want to check whether the base station is sending on the right channel, Kismac may be of use to you. This will show all modes that your Airport card supports, including dual-band base stations. It's also great for checking wi-fi coverage with the built-in signal monitor, which can chart signal strength as you walk around with laptop in hand.