AWUS036ACS Txpower problem

Hello,

Have ALFA adapter AWUS036ACS with 88XXau driver.
Can change TXPower, Power Management:off

wlan0 unassociated ESSID:"" Nickname:"<WIFI@REALTEK>"
Mode:Managed Frequency=2.412 GHz Access Point: Not-Associated
Sensitivity:0/0
Retry:off RTS thr:off Fragment thr:off
Encryption key:off
Power Management:off
Link Quality=0/100 Signal level=0 dBm Noise level=0 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0

iwconfig wlan0 txpower 30
Error for wireless request "Set Tx Power" (8B26) :
SET failed on device wlan0 ; Operation not permitted.

Any solution ?