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5 GHz Wi-Fi network is occasionally disabled (radar signal)

Every now and then, the 5 GHz Wi-Fi network is disabled and the FRITZ!Box shows a message with "RADAR"? ✔ Here you can find out what that means.

The 5 GHz Wi-Fi network of a Mesh Repeater (for example FRITZ!Repeater) connected to the FRITZ!Box is occasionally disabled. One of the following messages is displayed in the event log of the FRITZ!Box:

  • "5 GHz band cannot be used on the selected channel [...] for [...] min. because of check for higher-priority users (e.g. RADAR)"
  • "RADAR was detected on channel [...] (frequency [...] GHz); channel switched automatically because of higher-priority user"
  • "RADAR was detected on channel [...] (frequency [...] GHz), repeater on the 5-GHz-band deregistered from the access point for [...] min. (+ 1-10 min. additional RADAR waiting time, depending on the channel assignment)"
  • "Temporary channel change to channel [...] (frequency [...] GHz) until the check for higher-priority users (e.g. RADAR) on the configured frequency [...] GHz has been concluded (Zero Wait DFS)"

1 5 GHz Wi-Fi network is disabled for the search for higher-priority users

The FRITZ!Box makes the Wi-Fi network available in both the 2.4 GHz and 5 GHz frequency bands. However, Wi-Fi channels 52 to 140 of the 5 GHz frequency band are not only used by wireless devices, but also by radar systems (for example air traffic control, the military, and weather service), so-called higher-priority users.

To not disturb these higher-priority users, the FRITZ!Box initially only enables Wi-Fi channels 36 to 48 for the 5 GHz Wi-Fi network after a restart or change to the Wi-Fi settings. In addition, the FRITZ!Box checks the higher Wi-Fi channels for higher-priority users. The FRITZ!Box only switches to higher Wi-Fi channels if it does not detect any higher-priority users during the check (DFS wait time) that can take up to 10 minutes. Since the FRITZ!Box informs the wireless devices about the channel change in advance, the Wi-Fi connections of the devices are usually not interrupted.

Even during operation, the FRITZ!Box continuously checks whether the Wi-Fi channels it uses are still unused by higher-priority users. If the FRITZ!Box detects a higher-priority user, it switches to Wi-Fi channels 36 to 48 and searches again for up to 10 minutes for higher-priority users.

This behavior is also called Zero Wait DFS (Dynamic Frequency Selection). However, most Mesh Repeaters do not support Zero Wait DFS and must therefore disable the 5 GHz Wi-Fi network during the DFS wait time. This behavior is mandatory in all countries of the European Union.

2 Effect on the wireless devices

To ensure that the Wi-Fi network can still be used even while the 5 GHz Wi-Fi network is disabled on the Mesh Repeater (DFS wait time), the FRITZ!Box steers the wireless devices to the 2.4 GHz Wi-Fi network or to a different wireless access point if necessary:

  • The FRITZ!Box can seamlessly steer wireless devices that support the wireless standards 802.11k and 802.11v from the 5 GHz to the 2.4 GHz Wi-Fi network or to a different wireless access point.
  • The FRITZ!Box can only steer older wireless devices that do not support the wireless standards 802.11k and 802.11v from the 5 GHz to the 2.4 Wi-Fi network by briefly clearing the Wi-Fi connection. The FRITZ!Box cannot steer these devices to a different wireless access point.

As soon as the 5 GHz Wi-Fi network is available again, the FRITZ!Box steers the wireless devices back to the 5 GHz network or a different wireless access point if necessary.

Note:The FRITZ!Box displays wireless devices that support the standards 802.11k and 802.11v under "Wi-Fi > Wi-Fi Network > Known Wireless Devices" ("Wireless > Radio Network > Known Wireless LAN Devices") with the properties "11k" und "11v".

3 Optimizing the FRITZ!Box's Wi-Fi settings

In the factory settings, the FRITZ!Box is configured so that it can steer wireless devices to the other Wi-Fi network or a different wireless access point. This is not possible if different names were given to the 2.4 GHz and 5 GHz Wi-Fi networks in the FRITZ!Box or the other wireless access points were not correctly integrated into the Mesh. In this case you must optimize the Wi-Fi network of the FRITZ!Box.