I am using hostapd on the official Ubuntu image to use Rock Pi E as Wireless AP, however it appears that the TX Power of the RTL8821CU chip seem to be restricted to 12dBm.
I understand that the TX power is heavily regulated and depends on my country and channel but I am running it on channel 36 US and according to iw list output I am allowed 23dBm tx power, however I am unable to change the tx power using the following command,
rock@rockpie:~$ sudo iwconfig wlan0 txpower 23
Error for wireless request “Set Tx Power” (8B26) :
SET failed on device wlan0 ; Operation not permitted.
While I managed to get 434Mbps bitrate by explicitly setting ht_capab and vht_capab in hostapd config file, I am barely exceeding 60Mbps in iperf3.