Lots have been written about the best channels to use on 2.4GHz. The short word is that in a big installation you want to use channel 1, 6 and 11 as these are the only non-overlapping channels. So in say a big house, you’d want the basement atl channel 1, the 1st floor at channel 6 and the top at channel 11 to minimize interference.
For 5GHz much less has been writen about the best frequencies mainly because most systems just use a single 20MHz channel and these are non-overlapping, but it turns out there are considerations:

  1. There are general two sets of frequencies that are low (UNII 1) and high (UNII 3) or in Apple talk they are If you’ve got DECT phones (like I do!), the so called 6GHz DECT phones interfere in the upper 5GHz
  2. The upper band has 20 times the power of the lower so if you don’t have DECT, then you can use the upper
  3. If you use Wide Channel, then you have to have two channels free, so that means for 40MHz, you can use channel 36 and 44 and for the upper band, 149 and 147.

See the summary… see http://tidbits.com/article/10849
I was reminded by Apple product managers a few months ago while talking about AirPort issues that the lower band uses 1/20th the power of the upper band. That’s right: Choose channel 149, and your base station broadcasts signals at 20 times the power of channel 36! (The 5 GHz band, because of its shorter wavelength, requires more power to send the same quantity of data the same distance as a 2.4 GHz device.)
Power corrupts, however. The more power you use to broadcast a signal, the more potential there is for that signal to interfere with other networks, and to receive interference as well.
There’s a second problem with the upper band: it’s used for 5 GHz cordless DECT phones. These phones use an entirely different technology that can disrupt Wi-Fi performance without violating any FCC rules.
Finally, if you use so-called wide channels, which use 40 MHz of bandwidth to double 802.11n throughput, you’re down to just four possible channels (36 or 44 in the lower band, or 149 or 157 in the upper band).

I’m Rich & Co.

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