Wifi analyzer for DFS interference etc

[carl_townshend]

Hi All

We keep getting DFS events at one of our sites in the UK and it is causing us lots of issues.

Is there a way we can use an analyzer to find the source of these events?

Also, what spectrum analysis software could I use on my laptop to check for background noise and interference etc?

Many thanks

[Rasika Nayanajith]

I think first of all see how frequency those DFS event occurs and if you can predict when it is going to happen next. With that using spectrum analysis tool (Ekahau Sidekick/ AirMagnet Spectrum XT or Channelizer) you should able to see those in real-time. Channel change could be due to false-positive as well

Here is a very good talk about DFS. Also, refer to the below post on how to use Splunk to analyze those DFS events

https://framebyframewifi.net/2017/02/12/splunking-wi-fi-dfs-events/ 

HTH

Rasika

*** Pls rate all useful responses ***

[patoberli]

To add to Rasika, Cisco had several updates in the past to reduce the amount of wrong DFS events on some AP models (mostly the AC Wave2 series like 2800 and 3800). It typically also helps to reduce the channel width to 40 or even 20 MHz to reduce the amount of DFS events. 

[Rich R]

@Rasika Nayanajith& @patoberli have covered it mostly but I was going to say what APs & what software version & what channel width for exactly the reasons Pat mentioned.  We had this problem - all false detections.  Combination of software updates with the fixes Cisco put in + reducing channel width brings the false detections down to a tolerable level  Depending on AP model it's almost impossible to completely eliminate them as the chipset on some models is not as good at reliable DFS detection.

And you should also be aware some devices like motion detectors used for doors, security systems and lighting can use radar which can potentially be a trigger.  Also (UK) some GATSO speed cameras and red light cameras use radar (but unlikely to be that).

[carl_townshend]

hi

the access points in question are meraki mr74, the devices that connect are windows tablets with the Broadcom abgn chipset, this is in a new warehouse.

we are really struggling to find what it is.

sometime tmrw we are going to switch off all the tablets to see if it goes away.

you could be right about the lighting also, we could tell them to switch that on with no sensors.

any other ideas ?

[patoberli]

I have DFS events on the lakeside part of my buildings. Not sure, but my gut tells me some ship is using a radar in the 5 GHz frequency causing that. 

Haven't got any experiences with Meraki though, not sure if the mr74 are more or less prone for false DFS evens.