240AC Access Point - 5G channel width keeps changing back to 20MHz

[momo83]

I've purchased a 3 pack of the Cisco Business 240AC access points and have configured them to the point where they work perfectly. I have a gigabit internet line and I achieve almost 600mbit speeds through WiFi so good start so far. After a few days I suddenly realised the speeds become slow and after checking the settings the channel width has changed to 20MHz from 80MHz. After changing it back to 80MHz speeds go back to being impressive however the channel width change back to 20MHz after a few days again.

Why is it doing that?

• All AP's are behaving like this.
• All AP's are on the latest version 10.4.1.0
• I'm using a POE+ switch on all AP's (Cisco SG300 + TP-Link TL-SG108PE)
• Channels configured are (112, 108, 100, 104)
• RF Optimization is switched off.

[Scott Fella]

If you are 100% sure you have it manually set and there is nothing that "CAN" change it, then open a TAC case.  Why are you using those channels, maybe allow all the channels and see if that helps.  You are using DFS channels in which has to change if radar is detected.  Change the channels to allow all and then see what happens.

[momo83]

Hi Scott. I'm using those channels as they offer the best performance and after scanning all channels I found these are not used by any neighbours so I get no interference. Also I'm not near any radar installation so shouldn't be a problem. 

I've tried setting the AP's to automatic channel and channel width selection however they wouldn't go any higher than 20MHz which is why I decided to set everything to custom. 

I'll try your suggestion and open a TAC case as I really can't see where the issue is. I've upgraded to these from Cisco wap571 and I've not experienced any issues like this. 

[Rich R]

Never used this product before but generally speaking:

- the wider the channel the higher the risk of false positive DFS radar detections

- the cheaper the chipset the higher the risk of false positive DFS radar detections (some worse than others)

- TAC standard recommendation is to use 20Mhz channels as a workaround

If you can convince TAC to open a bug for it (and they can reproduce it) then you might eventually (think 6 months to a year) get a new version of code with a fix or improvement in behaviour (sometimes you might be able to get an engineering special with fixes before it's released)

Otherwise try using non-DFS channels if there are any in your region.