Why am I not able to change the 5 GHz channel width from 20 MHz to 40 MHz?

Zyxel_JoyLee

The most common reason is the selected 5 GHz channel cannot be bonded to 40 MHz.

For example, if the AP is fixed on channel 165, it can only use 20 MHz, because there is no adjacent 5 GHz channel available for 40 MHz bonding. In this case, the channel width option may stay at 20 MHz or cannot be applied.

Please check these points:

1. Check the current 5 GHz channel
   • If it is using CH165, change it to another valid channel such as 36, 40, 44, 48, 149, 153, 157, or 161.
   • Then try changing the channel width to 40 MHz again.

2. Check the radio mode

• If the 5 GHz radio is using legacy mode such as 802.11a only, it may only support 20 MHz.
  
• Use 802.11n/ac/ax mode if available.