Low speed of wifi interface


I’ve found that wifi connection on my board is too slow.
I’ve measured it with iperf: 11.6 Mbits/sec
At the same time, test from Andorid phone and Windows machine connected to the same network shows ~90Mbits/sec.

Can it be fixed?
BTW, my router is configured to a “Mixed n/ac” mode for 5G band. If I turn it to “ac only” mode, the board cannot attach to it.

$ /sbin/iwconfig wlan0
wlan0     IEEE 802.11  ESSID:"xxxxxx"  
          Mode:Managed  Frequency:5.18 GHz  Access Point: 50:C7:BF:8C:18:C8   
          Bit Rate=150 Mb/s   Tx-Power=20 dBm   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Power Management:on
          Link Quality=63/70  Signal level=-47 dBm  
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:1  Invalid misc:1   Missed beacon:0

Can anyone using Android on this board test wifi perfomance (preferably with iperf, but simple download speed over wifi network or another speed test could help)?