I'm using a pair of SXTsq 5 ac to bring cable broadband to a location where service is unavailable. Contract speed is 400/20, speed tests with wired connection consistently show ~420/21 Mbps.
However, try as I might, I can't get more than ~250 Mbps across the link. Distance is ~110 m, clean line of sight (clear Fresnel zone) except that the AP end is behind a single-pane uncoated glass window. Both ends are precisely aligned. The AP end is configured as Bridge and has a simple NAT router configuration. The station end is configured as Station Bridge and is a simple bridge. I'e tried adjusting power levels and switching channels (among other things), to no avail.
I've ruled out resource issues. When downloading ~200 Mbps, CPU usage is ~9% (AP) and ~2% (station). CCQ is usually 99 or 100%, never below 95%. UDP Bandwidth test (run on station in receive or transmit mode) gives ~450 Mbps.
I suspect interference from neighboring devices, though it seems unlikely because the issue persists in the wee morning hours. While it's conceivable that a neighbor might have 24/7 traffic (security cameras uploading to cloud, file sharing, infected, etc.), I have trouble on both 5.2 and 5.8 GHz and it's hard to believe that both are continuously polluted.
Here is a scan from the station:
AP # 0 is of course the one to which I'm connecting. APs # 1, 5, 6, 7 and 10 are mine and were idle during this test. APs # 2/3, 4, 8, 9 and 11 belong to neighbors.
How can I tell how much time the AP is spending deferring to other transmissions? How can I tell how many packets were garbled by collisions with other transmissions?
Besides interference from neighbors, what other factors could be causing poor throughput?
Thanks in advance for any guidance.