A few weeks ago, I noticed that our internet was really slow. Now that I have a laptop (running Hardened Gentoo,) I no longer use a wired connection to our router, and it was painful to download anything. Other family members experience the same problem.
When I ran 'sudo iwlist scan', I came up with more than one network. In fact, at one time, I was able to pick up at least 11 networks
(I forgot exactly how many). These included clearly-visible and prominent ones on channels 1 and 11, as well as ones on channel 9 and a few on channel 6 (which I suspect to be 108 Mbps systems) that turned up more rarely in the scans.
I looked at the iwconfig man page, as I remembered some potentially useful settings there. I set up this configuration for my system (I used the same settings on our router, except all I could configure was the channel, fragmentation, and RTS
ESSID: <our ESSID>
mode: Managed (not sure what Windows calls this)
channel: 5 (this had the least overlap with the most affected channels.)
Access Point: <our AP mac address>
Transmit power: max (for me, 100mW, or 20 dBm)
Power: all (power management setting.)
I have only tested for a few minutes during interference, but it seems to work well now. I emailed this list of settings to the Windows person in our household.
It goes without saying that if (big if) these settings also exist on Windows, they'll be hard to find.
I hope this helps others who run into the same problem.