802.11b and 802.11g (the most common) devices are usually referred to as operating at 2.4GHz (gigahertz). In fact, the signals for these devices can operate on one of eleven (11) distinct sections (or channels) within the 2.4GHz band. Some regions allow operation in thirteen (13) channels, however the U.S FCC defines eleven (11) channels. What this means is that you can configure your wireless adapter and access point to operate on slightly different frequencies than other networks in your area, to avoid interference and congestion. Each of these channels cover a frequency range of 22MHz; in other words, a device operating in each of these channels can operate at up to 11MHz on either side of the "center" frequencies listed in the following table.

If we study the frequencies used in these eleven (11) channels, and take into account that each channel can operate in 11MHz ranges either side (+/-) of its center frequency, the channels 1, 6 and 11 never overlap with each other. Channels that are separated by at least five other channels (or at least 2.5MHz) do not overlap. You can use this important piece of knowledge when you have wireless congestion issues; for example, in an apartment building with three wireless networks near each other, you can avoid congestion by getting the networks to run on channels that are sufficiently separated from each other, such as 1, 6 and 11. A heavily congested area may not provide the freedom to do this, however it is useful to remember.