Unable to increase tx power on RTL8821CU

aviartz · October 26, 2020, 9:07am

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.

igorp · October 31, 2020, 7:37am

Again … setting power will work on Armbian out of the box.

aviartz · October 26, 2020, 1:48pm

Does Armbian use something other than the 8821cu kernel module ? if so I can probably install that module over Ubuntu.

igorp · October 26, 2020, 2:01pm

You can’t install that module over “Ubuntu” since it uses completly different (better) kernel and different (better) driver.

aviartz · October 31, 2020, 7:37am

I moved to Armbian buster today, but I am still not able to change txpower.

igorp · October 31, 2020, 7:57am

Try this way:

sudo iw wlan0 set txpower fixed 3000

Also hostapd that is shipped with Armbian is patched to get the most out of it.

aviartz · October 31, 2020, 8:05am

I tried, it still stuck at 12dBm,

rock@rockpi-e:~$ sudo iw wlan0 set txpower fixed 3000
rock@rockpi-e:~$ sudo iw dev
phy#0
Interface wlan0
ifindex 4
wdev 0x1
type AP
txpower 12.00 dBm

igorp · October 31, 2020, 8:19am

Debugging this exceeds my reach - driver code comes from:

github.com

armbian/build/blob/master/lib/compilation-prepare.sh#L320-L329


	# Wireless drivers for Realtek 8811, 8812, 8814 and 8821 chipsets


	if linux-version compare "${version}" ge 3.14 && [ "$EXTRAWIFI" == yes ]; then


		# attach to specifics tag or branch
		local rtl8812auver="branch:v5.6.4.2"


		display_alert "Adding" "Wireless drivers for Realtek 8811, 8812, 8814 and 8821 chipsets ${rtl8812auver}" "info"


		fetch_from_repo "https://github.com/aircrack-ng/rtl8812au" "rtl8812au" "${rtl8812auver}" "yes"

You might find some hints there.

linger · June 27, 2022, 1:07pm

do you have any ideal for this problem？ I also stuck at this problem

root@rock-3a:/home/rock# sudo iw dev wlp1s0 set txpower fixed 2000
root@rock-3a:/home/rock# iw wlp1s0 info
Interface wlp1s0
ifindex 11
wdev 0x700000001
addr 80:91:33:93:4b:b5
type managed
wiphy 7
txpower 12.00 dBm
root@rock-3a:/home/rock# sudo iw dev wlp1s0 set txpower fixed 1000
root@rock-3a:/home/rock# iw wlp1s0 info
Interface wlp1s0
ifindex 11
wdev 0x700000001
addr 80:91:33:93:4b:b5
type managed
wiphy 7
txpower 12.00 dBm
root@rock-3a:/home/rock# sudo iwconfig wlp1s0 txpower 10dBm
Error for wireless request “Set Tx Power” (8B26) :
SET failed on device wlp1s0 ; Operation not permitted.
root@rock-3a:/home/rock# sudo iwconfig wlp1s0 txpower 30dBm
Error for wireless request “Set Tx Power” (8B26) :
SET failed on device wlp1s0 ; Operation not permitted.
root@rock-3a:/home/rock#