

Here are some reasons according to our understanding of the Wifi standard of why you may not be able to 
see 40mhz as easy as before.
 
1)If an AP is booting up, it will cause all existing AP’s to go back to 20Mhz for at least 30 minutes

2)If an AP detects a Beacon from an AP with 40Mhz Intolerant Bit Set. An AP will set this bit if they 
  have a legacy client. AP will go to 20mhz.
a.This basically means if there is a single legacy client connecting to an AP, it will kill all AP’s 
  within its range to go to 20mhz.

3)If a AP receives a message from its client with 40Mhz Intolerant Bit Set. AP will go to 20mhz.

4)If there is legacy or 20mhz only AP in the extension sensitive channel. AP will go to 20mhz.

5)If there is noise on the extension channel. If the noise is above certain threshold, the channel will 
  not be used. AP will go to 20mhz.




