The HT40 channel display on the Status-Wireless page has been extensively discussed in ticket 3951, but it looks like BrainSlayer removed the ticket entirely for whatever reason. http://svn.dd-wrt.com/ticket/3951
The bug is still not fixed for Atheros-based routers (showing an Upper extension channel instead of Lower and vice-versa). The fix would be easy, but he considers it incorrect to implement and said repeatedly that it works for him. But you see that it displays it wrong for you and also for others.
I would propose to report your issue in a new ticket on bug trac, but the registration there for new users is also locked, strangely. So yeah, we have no choice, but to switch to other firmwares with friendlier communities (you know which one I'm talking about).
If you choose to still use DD-WRT, then have fun with seeing HT40 channels displaying combinations such as 1+ -3, 2+ -2, 4+0, 11+15 or 13+17 ! As I see it, the situation won't change any time soon... _________________ THERE ARE NO STRANGERS HERE; ONLY FRIENDS YOU HAVEN'T YET MET.
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Thanks for your reply and letting me know that it is not particular issue for my router, but a common issue.
by the way, may I know can you actually get channel width HT40 work? because all my wifi devices cannot get the highest connection rate, 144MB/s at most, and max real data transfer rate above 80MB/s. Is it normal?
I can confrim the HT40 wireless status bug with Linksys E4200 too. It happens only with K2.6 images.
With K3.x it's correctly displayed.
Current image 28072 but this belongs to all of the last images I had tested.