I was scanning my wifi area to check for the best channel and noticed that my 2.4 Ghz channel is set to 20 Mhz. I was then looking at the modem settings and don't see a way to enable 40 Mhz channel width on my 2.4 Ghz. Can you please let me know how I can change this option?
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You would have to call Tech Support to change the bandwidth to 40 Mhz. However, if the modem or any router detects that the co-channel required for 40 Mhz operation is busy, it will revert to 20 Mhz. On a 2.4 Ghz channel, its usually very difficult if not impossible to find a channel that has a clear co-channel.
The CGN3ACSMR with V184.108.40.206 loaded has those bandwidth settings available.
If you are in a populated wireless area, 2.4ghz, at 40mhz, will likely make your neighbours cranky, but you'll go faster!
It's an Asus link, but the "Good Neighbour Policy" rules still apply - https://www.asus.com/us/support/FAQ/114481/
excerpt from link
"802.11n can combine two 20 MHz channels to form an effective bandwidth of 40 MHz. 40 MHz enables higher data transmission rates to be achieved as compared to 20 MHz. When you select 20/40 MHz mode, the router decide to use 20 or 40 MHz based on the interference/contention the router detected. Care should be taken when using 40MHz mode, the legacy client may not be connected to the router.
However, when using a wider channel bandwidth, there are fewer channels available for other devices, making more interference/contention with neighboring WLANs due to increasing overlap. In order to avoid excessive interference, the Wi-Fi Alliance develops an advice: setting 20 MHz in 2.4GHz as default. 40MHz is still appropriate for some situations, e.g. in a warehouse, but we do not recommend that using 40MHz in the 2.4GHz band for dense residential areas".
If the modem / router was following the rules, setting the Channel Bandwidth to 40 Mhz wide wouldn't do anything. This is due to the Clear Channel check, which is requested by the transmitting device, and actually carried out by the receiving device. It would show that the 20 mhz co-channel required for the 40 Mhz wide channel is occupied by another modem or router. In that case the transmitter defaults to 20 Mhz, regardless of the setting. This occurs on a broadcast by broadcast basis.
Anyone still using a Draft-N device, and there are a number of them around, might cause problems as you suggest as they were not tested for compliance for these particular rules.