Channel bandwidth on 2.4GHz is 40 MHz (on 5GHz it's 20/40/80 MHz)
This is with my MacBook Air Mid 2012 version. It's an AirPort Extreme type, which is a Broadcom BCM43xx card. It supports a/b/g/n. Let me know if this didn't answer the question, though...
- Here's a post I explained recently the really good wifi diagnostics built into OSX you can use to survey our APs, the speeds they report, etc. Also holding down option key and clicking airport icon in menubar will give you instantaneous readings on RSSI & transmit rate.
http://forums.smallnetbuilder.com/showpost.php?p=80754&postcount=4
- Also check
here, and/or software update for firmware updates to your Air, I know there have been a few for that model
- You can also just set your 2.4ghz for 20mhz channels, if you have other 2.4ghz activity that your AP and/or MacBook can see, that pretty much confirms that 2.4ghz 20mhz channels are all that will work for you, and you're just giving it more opportunity to look for unoccupied RF space that probably isn't there. You can set it for 40mhz all day long but it will back off if it cannot find the 6 consecutive channels with low enough noise for it to use. My iteration of that card tops out at 145Mb over 2.4ghz (it's a year or two older), so I essentially run 2.4ghz for connections that need distance over speed, and vice versa for 5ghz, it's just the trade off with 5ghz attenuating much sooner but also having more physical spectrum to work with. The only reason some access points even let you try to utilize 40Mhz 2.4ghz channels is by mandating that it never be the default option (as of the last few years) it just is too crowded already and many APs and client NICs won't even utilize it if it's there.
inSSIDer shows my neighbors' networks at 300, 130, 144, etc. I would think mine should be higher...
The thing you are missing is that if you see 3 networks each advertising those connection rates as their max, that means that the 300mhz network is automatically using a little over half of the available spectrum on 2.4ghz. In the US we have 11 channels to work with, each channel is 20-22mhz wide, but they are separated by only 5mhz. If he is broadcasting as using channel 3, for example, he's actually probably using all the spectrum of 1-6. Then each remaining network is only single stream so, hypothetically they are 9 and 11, that's your entire 2.4mhz band occupied with some slight overlap between the networks there already competing for some space. That's a little overly simplistic, and depends on signal strength over other APs and how good they think their own signal quality is and stuff. Ironically, many people in more crowded areas of 2.4ghz usage would get better performance with their TX power turned down a bit (but only if everyone did it).
http://en.wikipedia.org/wiki/List_of_WLAN_channels
