Re: Channel Width/Channel: 20MHz or 40MHz
 

Most cordless phones these days are DECT and that doesn't use the 2.4GHz band.

Microwave ovens do but if they leak enough to screw up WiFi they are a health hazard and if its long enough to matter a fire hazard.

The biggest problem will be AV senders but as they give abysmal results in the presence of a WiFi signal I expect any nearby will have been binned.

The most common signals in the 2.4GHz band are WiFi as just about every ISP dishes out a free WiFi router these days. Having several on the same channel (and with the overlapping there are only 3 "real" channels - 1,6,11) isn't the kiss of death but it will cause a slowdown. IMO this will only get worse as people shell out on dual channel WiFi kit in the hope of improving their speeds.

Re: Channel Width/Channel: 20MHz or 40MHz
 

Is your wireless adapter also N300 - an N150 adapter generally has a single antenna, so does not have the MiMo capability for spacial streams.

With the other traffic on 1 (strongest) and 6, there probably is room to use 40MHz, 13 extension 9.

The basic, no overlapping channel plan, is 1 - 6 - 11
The optimum, marginal overlap plan for EU spec, is 1 - 5 - 9 - 13 - giving room for TWO wide users.
The compromise 4 channel (US spec) plan, 1 - 4 - 7 - 11 and try to avoid 3 spacing with stronger neighbouring signals

Re: Channel Width/Channel: 20MHz or 40MHz
 

You can't expect people to use channel 13. Much kit only works with US spec, such as Broadcom cards, and other kit won't auto tune to 13 (lots of routers come default to auto) or some such other issue. Add to that the huge amount of advice on the net to use 1, 6 & 11 (US-centric of course, but it's all over the place) and you can't expect others to use channel 13.

If you can get away with using it yourself of course, it can be a relatively unoccupied channel.

Best to assume your neighbours will follow the US model when planning your setup. Their auto probably will if they don't change it and default fixed channels are always 1, 6 or 11.

Even if you can fit a wide channel in, you should only do so when you want to transfer a big file then switch back. Otherwise no-one else will be able to use the space when they need it. Only use what you have to on the 2.4Ghz band, not what you can. Just because it is free at the moment doesn't mean you can stick your towl on it.

Re: Channel Width/Channel: 20MHz or 40MHz
 

Best to assume that most people won't touch their wireless settings at all and use whatever the default comes as. This is very obvious if you try something like the Android "wardrive" app on your phone and leave it running when you take a walk - probably more default SSIDs than custom and with many Belkin routers the same security too - none at all.

From the strength of some WiFi signals I see I think others absolutely must be using the high power amps you can get on eBay. In addition to my normal WiFi I have a little Fonera+ running on an external antenna to produce a good signal in my garden and a public FON hotspot which gives me free access to the FON network. Despite that antenna being on my outside wall and indoors beating the Superhub in some rooms there are a couple of external SSIDs that compete with it in some rooms. One day when I'm bored I'll track down whose they are.