Hello   @Naceron 

Range extender receives data from the router wirelessly and then forward it to the Wi-Fi network clients. speed will decrease during the transmission. 

Besides the range extender works in 'half-duplex' mode in extender mode,  it can only talk to the main router or the wireless client device in either way, not the same time, the link speed at physical layer will cut to half. In that way speed will get reduced again. 

Thus the range extender are used usually for increase more coverage or kill wifi dead zone,  instead of boosting the Wifi speed. 

If you could wire extender to router via Ethernet cable and use RE in Access Point mode, the speed could  be higher.

Hope this answer your question. 

  Hello @Naceron 

In the AP mode, if the 2.4Ghz Wi-Fi speed is slower, you could check what's the Wi-Fi link speed on the network device.  How to check the associated/link speed on a wireless client. RE330 2.4Ghz Max Wireless link 300 Mbps at 2.4 GHz.If the Link speed does not reach 300Mbps,the 2.4Ghz Wi-Fi speed cab be capped by the network adapter of a device. 

In extender mode, the speed RE received from the router at the location of extender is also quite important. And to check if the RE's speed is reasonable,  we will recommend test speed as suggested in the troubleshooting guide and judge if the speed is normal.  [Troubleshooting] What should I do if Internet speed becomes slow via Range Extender?