Wi-Fi 5 GHz keeps dropping? Radar and DFS may be the reason

Why does my Wi-Fi 5 GHz channel switch off?

In France, part of the 5 GHz band is shared with priority services. According to the national frequency agency ANFR, these include weather, aviation, military and satellite communication radars. Météo France, for example, runs C-band weather radars on 5 GHz frequencies spread across the country to track rainfall. Home Wi-Fi that does not behave can disturb them and skew forecasts. ANFR says it sees such interference on weather radars very regularly.

To avoid that, home equipment must scan its band continuously for radar. Under the European ETSI standard for 5 GHz, a device must leave the channel within 10 seconds and not use it again for at least 30 minutes. That is why the band can take a while to come back: the router has to listen first and check that no radar is left.

Can I turn DFS off?

No. Disabling or modifying DFS is prohibited, and in theory it is not possible on consumer devices. Some routers let you prefer non-DFS channels, but that option should not be used to get around the rules.

There is a penalty for causing interference. Article L39-1 of the French postal and electronic communications code punishes disturbing an authorised service with non-compliant radio equipment: up to six months in prison and a 30,000 euro fine. If you have not tampered with DFS, you have nothing to worry about.

So next time the forecast is wrong and it rains anyway, the culprit may not be the weather presenter. It could be your box.