I'm unable to manually set the 802.11 mode for my atheros mini PCI radio cards (one is a Atheros 5413 chipset, the other is a 5212).  Here are my attempts/results:

root@smeshnode_03:/# iwconfig ath0 modulation 11g
Error for wireless request "Set Modulation" (8B2F)  :
       SET failed on device ath0 ; Operation not supported.
root@smeshnode_03:/# iwconfig ath0 hwmode 11g
iwconfig:  unknown command "hwmode"

Any ideas on how to set my cards for a, b or g mode?  (The 5212 card does not support a-mode, but both cards DO support both b and g).

(Last edited by Jim@JHUAPL on 4 Aug 2009, 13:28)

No one has any suggestions?

Try:
option 'hwmode' 'g' (without 11)
It woroks for me

doesn't seem to work. tried "11g" (as the default was "11bgn") and "g", and also "802.11g". iwconfig and the clients continue to show multi mode.

most docs i've found mentions nvram only.

# uci show wireless.radio0.hwmode
wireless.radio0.hwmode=g

# iwconfig wlan0
wlan0     IEEE 802.11bgn  Mode:Master  Frequency:2.462 GHz  Tx-Power=20 dBm   
          RTS thr:off   Fragment thr:off
          Power Management:off

what am i missing?

Thats normal. My 11g connections show "abgn" as well. The iwconfig output you see is feeded by cfg80211's compat layer which just reports nothing (or nonesense) for certain values.
The actual handling of b mode, g mode etc. happens within the drivers and hostapd.