Wi-Fi and the Problem with Radar (DFS)

Interesting this. It reminds me of when my dad used to work at NATS /CAA (uk air traffic body). I remember him getting complaints in the early 90s that people’s car locking systems failed to work on the car park next to the radar tower at Gatwick. Turned out the radar (or the huge electrical field created by the motors in the radar) created havoc. If I remember right it ended up being a question on the back page of the new scientist..

Primary user of 5GHz band is weather radar service. Operators of that are universally fed up with interference caused by misconfigured wifi devices, so you should do everything you can as to not interfere with that if you do not want to get huge fine from your local equivalent of FCC (in most other bands you will get a friendly warning that you are doing something you should not be doing, in 5GHz the enforcement is often swift as the amount of violators simply does not leave them much of a capacity for friendly warnings).

Years ago I had a customer who had deployed around 300 WiFi voice handsets in a hospital for the nursing staff to use. They ran into this problem, which ended up being really difficult to troubleshoot. The user-visible symptom was sporadic one-way audio, but we wouldn't get the trouble reports for hours and never with a precise time. The problem ended up being the access points dynamically adjusting their transmit power down on certain U-NII 2 channels when radar activity was detected. The voice path from phone to AP was fine, but the path from AP to phone was sometimes lost.

I have also run into issues with DFS in the past[0] without fully understanding what was wrong, until my friend let me know that this is a thing. Choosing a static Wi-Fi channel that's outside the DFS range, or limiting the selection of channels to exclude the DFS channels has worked well for me.

[0]: https://ounapuu.ee/posts/2024/11/11/openwrt-dfs/

I used to work in an office that had beautiful views over a big river. I remember that there were a lot of issues with the WiFi, despite having switched between all major Access Point manufacturers to try and get a properly working setup. In the end it turned out to be the radars of ships causing issues.

My outdoor UniFi APs used to get these alerts but I always thought it was the planes flying overhead. They fixed something on my APs or region that caused the alerts to go away.