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One of the terms I've seen defined in the wpa_supplicant for Linux devices using an ad hoc network is "frequency=2412", and I have to admit its function is obvious, but I was wondering if anyone could point me at a definitive list of allowable frequency values??

Or is this the correct answer: http://www.moonblink.com/store/2point4freq.cfm

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802.11's channelization of the 2.4 GHz ISM band puts the channels' center frequencies 5 MHz apart:

  • Channel 1 is 2412 MHz
  • Channel 2 is 2417 MHz
  • Channel 3 is 2422 MHz
  • Channel 4 is 2427 MHz
  • Channel 5 is 2432 MHz
  • Channel 6 is 2437 MHz
  • Channel 7 is 2442 MHz
  • Channel 8 is 2447 MHz
  • Channel 9 is 2452 MHz
  • Channel 10 is 2457 MHz
  • Channel 11 is 2462 MHz = maximum FCC / North American channel
  • Channel 12 is 2465 MHz
  • Channel 13 is 2472 MHz = maximum ETSI / European channel

Because 802.11 channels in 2.4GHz are 22MHz wide (802.11b) or 20MHz wide (802.11g, 802.11n HT20), the overlap their neighbors quite a bit. Channels that are 5 channels numbers apart are considered non-overlapping. So 1, 6, and 11 are commonly used non-overlapping channels.

Even though the band starts at 2400MHz, and the channels extend at most 11MHz down from their center frequencies, the center frequency for channel 1 was chosen to be 2412 to leave a little bit of room at the beginning of the frequency to be sure that even poorly-designed transmitters don't accidentally transmit outside the band. A similar thing was done at the high end of the band.

802.11n can use 40MHz-wide channels in 2.4GHz. For that, two contiguous 20MHz channels are used. These are 4 channels apart, so "channel 1 + channel 5", or "channel 7 + channel 11". One channel is considered the "primary" or "control" channel, while the other is considered the "extension" channel. The notation usually lists the control channel, followed by a "+1" or "-1" to indicate if the extension channel is above or below the control. So "1,+1" is "channel 1 + channel 5" with control on channel 1, and "11,-1" is "channel 7 + channel 11" with control on channel 11. But some software that deals in frequencies will list a 40MHz-wide channel by its center frequency. So in the case of "1,+1", the center frequency would be the same as the center frequency for channel 3 (2422 MHz), and "11,-1" would be the same as the center frequency for channel 9 (2452 MHz).

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