FRITZ!Box 3390 Service - Knowledge Base
Status message "Radar detection (DFS wait time) triggered by channel assignments; 5-GHz temporarily unavailable"
The 5 GHz frequency band is not only used by wireless devices, it is also used by radar systems (for example air traffic control, the military, or weather service). To ensure that such radar systems are not subject to interference, the government granted them primary user status. Wireless devices that use a wireless channel from 52 to 140 must therefore detect primary users and use Dynamic Frequency Selection (DFS) to automatically avoid them.
Scanning for primary users
If the FRITZ!Box is using one of these channels, according to regulatory requirements, it must wait up to 10 minutes before allowing the 5 GHz frequency band to be used. The status message "Radar detection (DFS wait time) triggered by channel assignments; 5-GHz temporarily unavailable" is then displayed in the event log of the FRITZ!Box. The FRITZ!Box may not allow wireless devices to use the 5 GHz frequency band until the wait time has elapsed. The wait time always begins when the 5 GHz frequency band is enabled (for example after restarting the FRITZ!Box) or after the wireless settings are changed. If you change the wireless settings during the wait time, then the timer is reset. Wireless connections are automatically re-established once the wait time has elapsed. The scan for primary users is then continued; however, this does not have any negative effects on the 5 GHz frequency band.
Note:If the FRITZ!Box uses the same wireless network name (SSID) for the 2.4 GHz and 5 GHz frequency bands, then wireless devices can register with the FRITZ!Box's 2.4 GHz frequency band during the wait time.
Recognizing primary users
If the FRITZ!Box detects a radar system, it must automatically switch to a different channel, even if the channel is fixed. The status message "RADAR was detected on channel xxx; channel switched automatically because of higher-privileged user" is then displayed in the event log of the FRITZ!Box.
Note:In most cases it does not make sense to permanently switch to channels 36 to 48 if primary users are occasionally detected, since you can achieve a greater range and better throughput with the higher channels.