sudo lsusb | grep Atheros
Bus 001 Device 005: ID 0cf3:9271 Atheros Communications, Inc. AR9271 802.11n

lsmod | grep ath
ath9k_htc              56078  0
ath9k_common           21766  1 ath9k_htc
ath9k_hw              415436  2 ath9k_common,ath9k_htc
ath                    18741  3 ath9k_common,ath9k_htc,ath9k_hw
mac80211              532034  1 ath9k_htc
cfg80211              427855  4 ath,ath9k_common,mac80211,ath9k_htc

iwconfig wlan0
wlan0     IEEE 802.11bgn  ESSID:off/any
          Mode:Managed  Access Point: Not-Associated   Tx-Power=20 dBm
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off

airmon-ng start wlan0
Interface   Chipset     Driver

wlan0       Atheros AR9271  ath9k - [phy1]
            (monitor mode enabled on mon0)

sudo iwconfig wlan0 channel 1
Error for wireless request "Set Frequency" (8B04) :
    SET failed on device wlan0 ; Device or resource busy.

uname -a
Linux raspberrypi 4.4.13-v7+ #894 SMP Mon Jun 13 13:13:27 BST 2016 armv7l GNU/Linux