As ukhardy07 has said, 2.4Ghz WiFi should ideally be on channels 1, 6 or 11. These are non-overlapping channels. Ideally, all surrounding networks should also be on these channels as access points running on the same channel, with different SSIDs, will "work together" efficiently to share that channel. As soon as someone starts broadcasting between these channels (2-5 & 7-10), this is no longer possible, and all access points see each other as interference and are unable to "work together", thus reducing overall speed and reliability for everyone concerned.
I do recommend you invest in a WiFi scanner like inSIDDer - it can show up many things. For example, I have a lovely neighbour next door who has suddenly started to beam some WiFi device on channel 3, with SSID "MINE" (about sums him up). I was running happily on channel 1, until I noticed this. He's now effectively destroyed any meaningful speed on channel 1 (channel 3 overlaps mainly with 1) and partially channel 6 (channel 3 overlaps slightly with 6), meaning I've had to move up to channel 11 (which thankfully is mostly empty).
It could be that you have some access points around you not playing nice with the 1/6/11 rule. Also, you may have some really selfish neighbours who insist on using 40Mhz bands (rather than just 20Mhz) which takes up 2 whole channels of the 2.4Ghz spectrum, which can really mess things up for single band APs running on 1/6/11 as the extra 20Mhz channel is normally a +/- 5 offset from the main one. A WiFi scanner will be able to show you this. My APs can run in this mode but it is pointless if the spectrum around you is crowded (which mine is) as no speed-up will be gained (plus devices have to actively support 40Mhz anyway).
From experience, this is how I go about choosing a good channel:
1) Fire up inSIDDer and look at what the picture is. If I can find a completely empty channel 1, 6 or 11, assign the AP with that.
2) If 1, 6 and 11 are all in use, identify which of those channels have the lowest WiFi signals on them, and choose that channel.
3) If it happens to be that all 3 channels are roughly equal from analysis of 2 above, I then begin to consider the speed that each network is running at (inSIDDer tells you this too). In general, higher speed WiFI standards (like the 144 Mbits/sec "n" standard) are going to utilise more channel bandwidth than the older 54 Mbits/sec "g" standards. So in this case I choose a channel where all APs are using an equal or lower speed standard to what I'm running.
4) Avoid channel overlapping at all costs. If you find just one channel where some "idiot" is broadcasting between 1 and 6, or 6 and 11, move to the remaining channel which has no overlap. If this is unavoidable, set your channel to the same channel as where most of the other APs are running.
5) Run speed tests and move your AP channel around (taking into account all of the above) until you find a channel where you get the most reliable and strongest signal. Be aware that inSIDDer does not show you everything. As MrSaffron has said, you may have interference happening on some channels which inSIDDer cannot show you.
Finally, if you do have chicken wire in the walls of the flat (as ukhardy07 has also suggested), might be time to move to something like the
Devilo WiFi Powerline kits so you can expand connectivity through your mains ring, opening it backout to WiFi in rooms where you need it.
Edited by deleted (Fri 08-Aug-14 10:07:50)