Wireshark on OS X: I can configure my Airport channel, but how about bandwidth?

Question

This is what I currently do to capture 802.11 packets with Wireshark on my Macbook Pro

1. From my AP, I set the channel to 40 and channel bandwidth to 20MHz.
2. From Terminal, I set the Airport channel using: "airport --channel=40".
3. From Wireshark, I set my wireless interface to monitor mode.
4. Start Wireshark capture.

"airport -I" does not display any information about channel bandwidth, so I'm not sure if it knows how wide of a channel to listen on. This is why I set the AP's channel bandwidth to 20MHz - to give the Macbook Pro a better chance of capturing the packets. So, how can I set the channel bandwidth (using, I presume, the 'airport' tool)?

Answer 1

This comment seems to hint that adding "+1" or "-1" after the channel number might specify that the channel above or below should be included to get 40MHz.

The output of airport -s here shows some networks as having "100,+1" as the channel, so, if that's the syntax, you might put a comma between the channel and the +1/-1.

Trying both with and without the comma produced no errors on my Mountain Lion machine, but, then again, trying with the channel being "100spinach" also produced no errors, so maybe they're just calling strtol() without checking what follows last digit and don't support setting the channel width (the CoreWLAN framework, which I suspect the airport command uses to set the channel, supports setting the channel width).