I very recently got a Oculus Quest 2 and the main reason I got it was to play VR games on my PC. I soon found my problem was a severely unusable amount of lag, I checked whether my PC could run it and it more than could and due to that and the type of lag it was I was able to boil it down to network / internet lag. I'm a distance away from my router but that's not the only reason, the router itself is not very great but I was think about getting an ethernet cable. Basically the questions I have are, will the cable even help with connection to my pc with how bad my router can be and if only my PC has a good connection will I be able to use it or will the headset also need a better connection.
Probably ok if your PC is Ethernet wired to your router and the 30ft is line of sight and does not include floors/walls. Also, your 5Ghz wifi is dedicated (non-switching to 2.4Ghz band) and you are the sole 5Ghz usuer. Please google for Air Link requirements like this;
In any case, try Air Link out and see for yourself. Does not cost you anything if you initially stick with Q2 cross-buy games;
The other option, for AirLink, is to buy a dedicated router for it. You can get a WiFi6 router for less than $100. Put it in the room with the PC, connected to the PC by Ethernet, and set up the WiFi for the Quest to use. That will give you a strong signal near your PC, and probably much better range than your ISP modem.
If you do run an Ethernet cable from your modem for internet connectivity, plug that into the WiFi6 router, and then run another Ethernet cable from the router to the PC. The router will then distribute internet to your PC and to the Quest.
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