What is the best wireless channel to use ?

WiFi networks often suffer from interference from other wireless networks in the area, cordless phones, EMI/RFI interference from power supplies/routers/modems, etc.

Even though some wireless routers/access points can be configured to automatically choose the best channel, their algorithms can be obscure, the majority simply default to channel 6, and it is a good idea to survey your site and manually pick the best channel to use.

Since wireless channels generally overlap (as explained in more detail here), you should find other networks in range and what channels they operate in.

Under Windows Vista/7/2008, the default GUI wireless network list does not display the channels access points use. To find the channels, you have to do the following:

1. Navigate to Start > Run, type: cmd to enter command prompt
2. Type: netsh wlan show all
2a. Alternatively, type: netsh wlan show networks mode=bssid

This will display a list of all wireless networks in range, along with the network channel, signal strength, and security type used.

Ideally, you should pick a channel that is at least 3 channels apart from those used by other networks in the area.

Once you identify good non-overlapping channels, you can actually set your access point and monitor/compare the signal at one of your distant client devices. This can help in final fine-tuning for the best possible signal, as some channels may experience interference from other sources that are not detected as neighboring networks.

Notes:
The only completely non-overlapping 2.4GHz wireless network channels in the U.S. are 1, 6 and 11.
Most routers are preconfigured to use channel 6 by default, so you may want to avoid it.
You should try to keep your wireless router away from Cable/DSL modems, power supplies, and other possible sources of electromagnetic interference (EMI).