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Although 802.11b and 802.11g devices are designed to share the airwaves with neighboring networks, it is best to find a clear channel for several reasons, chief among these:
1. When your neighbors' networks are busy, there is less available bandwidth on those frequencies for your data, reducing your performance
2. Your Access Point (AP) and wireless devices may not hear your neighbor's weaker wireless signals, causing degraded performance due to collisions
3. Your neighbor's networks may not be entirely 802.11b or 802.11g compliant. Some "advanced" technologies are known to interfere with 802.11-compliant systems instead of sharing the airwaves with them.
In order to find a completely clear channel, you need to choose a channel that is 5 or more channel numbers away from your neighbors. This is not always possible, particularly in heavily populated areas. So do your best. Tools such as Vistumbler or inSSIDer can help you visualize the WiFi landscape.
You need to understand that the wireless channels translate to a radio frequency. Channel 6, for example, is 2.437 GHz (or 2437 MHz). Each channel up or down is 5 MHz away. However, and this is key, Wi-Fi signals are 20 MHz wide! So when you set your Wi-Fi device to channel 6, you actually are using the frequencies of channels 5, 6, 7, and half of 4 and 8.
So consider the situation below when 3 wireless networks are on 3 different, but adjacent channels, 5, 6, and 7. They may be different channels, but they are using much of the same spectrum and, as a result, they will contend with each other.
This is why it is recommended to try to be at least 5 channels (25 MHz) away from your neighboring networks. By doing so, you avoid overlapping the frequency spectrum that their networks use. By moving the network 5 channels away (6 minus 5 equals 1, or 6 plus 5 equals 11), you avoid any overlap. As follows:
Notes: The channels available are governed by local regulations. You may have different channels available to you.
ed: Some tests have shown that the minor overlapping of channels does not degrade performance of Wi-Fi systems, allowing for four nearby networks to share the available spectrum. This article discusses both three and 4-channel placement:
How do you determine what channels you and your neighbors' networks are operating on?
- You mention if user specify chan6, it's using 5,6,7 and half of 4 and 8. What happen if user specify chan11, does it imply 10,11,1 and part of 9 and 2? - No, the channel do not cycle. with channel 11 you use 10, part of 9, and let's say some "non defined" channel over 11, but it's still safe to use, it's been designed for it.
Very straight forward and helpful, thank you much.
Please say about tools like inSSIDer and Vistumbler which can list the channels neighbouring wifi devices use
You mention if user specify chan6, it's using 5,6,7 and half of 4 and 8. What happen if user specify chan11, does it imply 10,11,1 and part of 9 and 2?
I realize this articles a bit old, but one question: Its reccomended to be 5 channels away, but I can't ideally do that given the landscape of all the wifi's around. Sooo does amplitude take the next precidence (aka the y axis in inssider?), aka, distance between one router and another?
Thanks for the guide, I understand this now :)
so if i were to set up a channel of say "11"..a relative of mines uses the same channel...his frequency is basically interrupting mines correct?..so if i set up another channel where i'm 11 and his is 5..there wouldn't be much of a disruption?