We've suddenly seen a cluster of DFS detections that seem to be limited to a specific area of our campus. We are pretty close to an airport and Coast Guard station but there is no fixed radar licensed on this band anywhere in our state. It's possible that we're seeing glints of radar from military aircraft, however it seems that this would show up in a larger area of our footprint and it's not. I'm wondering about the specifics of the DFS detection mechanism in our A/Ps. Does the scanning radio look for any energy in this band that doesn't have OFDM or QAM modulation on it and assume that it's radar? I'm wondering if we're seeing a babbling wi-fi device.
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Hope this perspective helps.
Thanks for initiating this discussion ! To address the first part of why you are suddenly noticing DFS detections, its because we added DFS detection events into the Alert Hub and also on the AP details page on our dashboard earlier this month. These same DFS detection events were being captured in the event log all along and to raise awareness of potential impact of DFS hits, we decided to add this additional visibility. You can find additional details on this and potential actions to consider captured here: https://documentation.meraki.com/MR/Radio_Settings/Dynamic_Frequency_Selection_(DFS) . Do feel free to reach out if you have additional questions or any feedback you may have on this new visibility.
Thank you for this kNeil. Yes the additional visibility for DFS events is very helpful. After searching the logs though, it does appear that this is a recent spurt of activity, which goes back to my original question regarding the criteria for declaring a DFS event. Is the radio looking for a particular chirp pattern in radar? Some radars use chirp, some don't, some are pulsed while others are continuous wave, and none of them have Automatic Transmitter ID data embedded in the signal (this would be bad for tactical reasons). So how does the radio determine that it's radar and not some stray noise from a misbehaving 5ghz wi-fi client device?
Hope this perspective helps.
Thank you again kNeil. These are the kinds of specifics I was looking for.