Originally Posted by WDFan1970
When 40 MHz channels are used in 802.11n at 2.4GHz, 82% of the legal spectrum is allocated to that "One" channel. That means there's an 82% likelihood that your neighbors will be interfering with you...whether they're using 40MHz or 20MHz.
So basically, if YOU are using 40MHz channels, and your neighbors have WiFi of *ANY* sort in the 2.4GHz band, 82% chance they will interfere with yours.
2.4 GHz has only THREE channels that are considered "Non Overlapping." In reality, there is a LITTLE overlap. The channels are 1, 6, and 11.
Channel 1 overlaps with channels 1 thru 3.
Channel 6 overlaps with channels 4 thru 8.
Channel 11 overlaps with channels 9 thru 13.
If you use 40 MHz channels, then Channel 5 overlaps with channels 1 thru 7, and channel 9 overlaps with channels 3 thru 11. See? No matter WHICH channel you use, they overlap the others with an 82% likelihood.
This is based on United States frequency allocation. Other "regulatory domains" have different results.
So basically, 40 MHz channels are a HUGELY TERRIBLE thing to do in a "Shared" space. Only if you live out in the forest, or roughly 500 feet from the nearest neighbor, will you EVER get a clean spectrum. And if your city has Municipal Wifi: It's ALL OVER.
If your boxes do NOT have an Auto channel-width, then you are far better off using 20 MHz channels.
If you are using *ANY* 802.11b/g devices, you're better off leaving your max throughput set to 54Mbit / second, because there's VERY LITTLE advantage to having 802.11n in "Mixed Mode" with other devices.
All of these things I'm describing are generally called "Coexistence Problems." And it's a major limitation of WiFi. But it's NECESSARY to guarantee interoperability with older devices. The presence of so much as ONE 802.11b client in an 802.11b/g network slows performance dramatically. The presence of ONE 802.11 b or g device in a 802.11n network severely limits performance.
It's just the way it is.
Read the "Backward Compatibility" section of this wiki article: http://en.wikipedia.org/wiki/802.11n
to see more.
That's why WD stresses in the user manual: "The recommended setting on Wireless N routers is 802.11n-only..." because they know that "Mixed Mode" destroys high-throughput WiFi capabilities.