I just bought a second hand Asus rt-ac51u, since it was supported by OpenWrt and had a USB port.
Installation went fine and I got it running easily. However STA + AP configuration has been much more demanding. I have it now running, but download is quite slow through wlan.
I have set one radio to work only in client mode (5 GHz) and the other only as a master (2.4 GHz). I share mobile data from my cell phone (4G/LTE, 150 mbs limited).
It works just fine. I get internet access from lan and wlan.
The problem is speed. If I test using Speedtest in the net (or app) I get about 50 mbs download and 25 mbs upload from directly from the phone or from a PC connected to lan port. But if I connect the PC to 2.4 GHz, I get about 3 Mbs download and 25 mbs upload.
I get the same 50/25 mbs also from OpenWrt using speedtest-netperf script.
Th 2.4 GHz wlan seems to be working OK between OpenWrt and PC. I can transfer a 25 MB file in 10 s in both directions. So there must be something else limiting the performance. Top doesn't show high CPU usage.
So what is causing this slowness?
Also it would be nice to have both radios on 2.4 GHz or at least both Client and a Master on 2.4 GHz. I tried to do that any many different ways. It even worked for a while, once I turned off mobile sharing the whole wireless system stopped working. No access via 5 nor 2.4 GHz and no recontact to my mobile.
I also couldnĀ“t get the other radio to work at 2.4 GHz. I can choose 2.4 GHz, but it wont work as a Client nor a Master. 5 GHz it works OK.
STA + AP should be possible on the same radio, but only one channel/radio is available.
5 GHz has very limited range here due to brick walls. That's why I would prefer only 2.4 GHz, which is not at all crowded here, just one station from the neighbor can be seen.