Routers are required to leave some Wi-Fi channels when they sense radar, which can freeze calls. Here is why it happens and what you can do about it.
If your Wi-Fi sometimes drops for a few minutes and your video call freezes, your router may have heard radar. A feature called Dynamic Frequency Selection, or DFS, makes it step aside for military, satellite and weather radar. Then it returns on a different channel. The router's event log may show the word "RADAR" afterward.
Radar has priority on large parts of the 5 GHz Wi-Fi band, according to ASUS. When the router leaves, phones and laptops fall back to the slower 2.4 GHz band. In the United States, FCC rules require a router to listen for radar for 60 seconds before it uses one of these shared channels. If it hears radar, it must stop within 10 seconds and stay off that channel for at least 30 minutes. DFS is on by default, and the FCC requires it to stay that way in the shared bands.
The radar most likely to bother a home network is at airports, not military sites. The FAA runs 45 Terminal Doppler Weather Radar systems protecting 46 of the busiest US airports. They spot wind shear, a sudden change in wind speed and direction that has caused accidents. They transmit between 5600 and 5650 MHz, in the middle of the 5 GHz Wi-Fi band. The FAA says no wind shear accident has occurred at a protected airport since the system started in 1994.
The rules have teeth. In August 2019, the FCC proposed $25,000 fines against three wireless internet providers after their equipment interfered with weather radar at San Juan International Airport in Puerto Rico. The FCC said each had turned DFS off. Those were outdoor links, not home routers.
The 60-second listen happens every time a router starts up on a shared channel. That is why 5 GHz can take longer to come back after a restart. ASUS says the wait can run from one to 10 minutes depending on the country. In Europe, the standard demands a 10-minute check on channels that overlap the weather radar slot.
Using these channels is legal and fine for most people. Only channels 36 to 48 and 149 to 165 are radar-free in the US. If you live near an airport or military base and the interruptions are frequent, a fixed radar-free channel may help. FRITZ! suggests pinning the router to channels 36 to 48 if radar is detected continuously or every hour.
If calls freeze often near an airport, pin your router to a radar-free channel, and accept a lower top speed in return for steadier Wi-Fi.
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