FRITZ!Box 4040 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 installations (for example for use in air traffic control, by the military, or the meteorological service). To guarantee the interference-free operation of these radar installations, the government granted them primary user status. Legislation stipulates that wireless devices using wireless channels from 52 to 140 must detect such primary users and use Dynamic Frequency Selection (DFS) to automatically avoid them.
When the FRITZ!Box uses one of these wireless channel, it continually checks whether the channel is also being used by a primary user in the vicinity. If this is the case, it waits up to ten minutes, as legally required. During this period you cannot register any wireless devices. If you change the wireless settings during this time, then the waiting period starts again from the beginning. After the specified time, wireless connections are automatically re-established.
Note:In the vast majority of cases it does not make sense to permanently switch to channels 36 to 48 because of occasional radar detection, since the higher channels in the 5 GHz frequency band usually offer a greater range and better throughput.