• Hi, Can anyone help me with this, please?

    I am testing one router from a vendor. This router on the 2.4GHz seems to be transmitting a 40Mhz bandwidth which takes up more than 50 of the spectrum. I need to raise a fault with the vendor but have been trying to get the standard from the IEEE 802.11 2009 amendment regarding the selection of BW but cant seems to find it anywhere.

    I was just want to clarify on what conditions it is allowed to use the 40Mhz BW for 2.4GHz. as if I remember correctly if the adjacent secondary channel is used by 802.11 or non 802.11 medium it should auto fall back to the 20MHz transmission. Is this correct?

    You help is much appreciated. !



  • Off the top of my head: 40MHz channels appeared with 802.11n. The band was not specified, so yes, you can use 40MHz on 2.4GHz. You won't find any statement that prohibits it. However, if you find a client device that can make use of it, let me know! It would be silly to make 40MHz default or the only choice on 2.4GHz.

    If the secondary channel is busy the device will wait for it to become available. In a busy environment 40MHz may therefore be slower than 20MHz since it has to wait for both channels to be clear at the same time. 802.11ac provided for dynamic width (and more choices for width).

  • By Howard - edited: May 31, 2018

    There is also a "40 MHz intolerant" flag/setting.on the client side (per the IEEE,  it could also be set by an AP).   This was first introduced in 802.11n.

    This can help tremendously, but as I said in 2016, from what I have seen not all AP's feel they are bound to obey it.   Things may have changed since then, but I doubt it.

    I again looked through the IEEE spec, and this flag is also mentioned in the section describing Channel Reports -  I hadn't seen that until now.   So the newest AP's and clients should both be obeying it.

    However, as I have said before - just because the IEEE mandates something, does not mean that industry, or the WFA, follows or demands it too.

    I looked through both the WFA 802.11n and /ac test plan documents, but did not find that it was tested for in either one.   It is also not mentioned in the WFA's Coexistence test plan.. 

    Please clarify, in your post you wrote "50".   Did you mean 50%, or 50 MHz ?     If you meant 50 MHz the power amplifier in the radio may be being overdriven (set to too high a power)    .   If 50%, then 50% of what ?  

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