Very slow wifi speed

I have recently bought a TP-Link WR841N v10.

In general it is working ok, but the wifi speed never goes above 840kbps. Via etheet it can reach as high as 10-20 Mbps. But wifi seems to be capped at 840 kbps.

It is expected ? While I do understand that speed can be slow at 2.4 GHz, but I still think that the speed is uaturally low. I have WPA2-PSK authentication, chael width 20MHz at bgn mixed mode, WMM activated.