ALFA AWUS036NH RAILINK RT2870/3070 failed to set txpower help

[constantinex]

hi there
i just bought the alfa awus036nh Ralink RT2870/3070 -wifi card
but when i try to set txpower it not changed

iwconfig
wlan1     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:on
          
eth0      no wireless extensions.

lo        no wireless extensions.

wlan0     IEEE 802.11bgn  ESSID:"COA-OLC"  
          Mode:Managed  Frequency:2.412 GHz  Access Point: FC:5B:39:E0:D5:C2   
          Bit Rate=130 Mb/s   Tx-Power=16 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality=63/70  Signal level=-47 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:15   Missed beacon:0