Page 2: Wi-Fi Tips #3 and #4 - Channel Width and Aiming Antennas
(See Page 1 for Tips on Wi-Fi Network Names and Mitigating Congestion)
3. Don't use "Wide" 40MHz channels on 2.4GHz. Some routers (not Apple's) will allow you to use "Wide" channels on the 2.4GHz band. The problem is this band is so congested that you'll likely just wind up making things worse instead of better. Bluetooth lives here, too, and will appreciate the breathing room. Plus, Apple made the decision years ago to not support these wide channels at 2.4GHz, so even if your router allows you to enable it your iPhone and MacBook won't use it.
On your 5GHz radios 40MHz channels are perfectly acceptable (again, your Apple router takes care of this for you). And with 802.11ac (5GHz only) you may wind up using 80MHz or even 160MHz channels. Just remember that current 5GHz implementations only have enough room for TWO (yes, 2) 160MHz channels, so choose wisely. The good news is that current 802.11ac routers use "cognitive radio" technology. This means they listen before they talk and that will ratchet down from 80MHz (or 160MHz) to something lower if they see another router communicating in the same band. Smart.
4. Be smart about antenna orientation. If your router has internal antennas (as most new models do), make sure to use them in their natural orientation. Put simply: if the router has feet, use them as feet (as opposed to laying it on its side). Some routers have feet on two sides and give you placement options, so feel free to capitalize upon this flexibility.
For routers with those adjustable, "rubber ducky" antennas, Alf recommends pointing one straight up and one flat out. This is because radio reception is maximized when both client and access point have matched polarization (antennas pointing along the same plane).
Some client devices have antennas in vertical orientation, some horizontal. The current crop of MacBooks, for example, have their antennas in the black plastic part of the hinge in a horizontal orientation.
Those tips should get you started. Give Mac Geek Gab 509 a listen to learn more about beamforming, the future of Wi-Fi, how your router decides what country it's in (and what channels it can use!), the future of iStumbler (and other products from Alf) ... and more!