Rpi3b+ as repeater


I'm trying to set up a raspberry pi 3b+ as a simple wifi repeater. I've got the recommended build
(OpenWrt 21.02.1 r16325-88151b8303) for the rpi3b+ up and running with luci and travelmate installed. So far everything seems to work fine except for one thing: the device refuses to switch to AP-STA mode, despite being capable according to iw list. Whenever I activate the AP-interface, the client interface(uplink) gets disconnected and disabled.

I'm honestly not even sure where to start looking. Before I dig deeper into this, does anyone know if this is a known problem with the pi3b+? Has anyone ever gotten ap-sta to work on this model? Google only takes me to lots of unresolved problem reports like this one: https://forum.openwrt.org/t/how-to-configure-raspberry-pi-3b-as-a-repeater/46202

Two thoughts here:

  1. I have not tried using a Pi as a repeater, but IIRC, the wifi chipset in many of the models doesn't support simultaneous sta + ap operation. I could be wrong about this, but see point 2...
  2. All of the Pis have pretty poor wifi performance in general in terms of the radio/antenna situation. They all have a single radio (per band, where applicable) that is a 1x1 setup with a small antenna that is actually part of the PCB itself. Therefore, they are not well suited to operating as an AP both for general performance and range.

That said, you will be much better off if you use a standard AP or router with 2 radios and MIMO capability.