Fail to select channel after radar detected

RouterOS Wireless Networking
1

Hi guys, I’m running 2 LHG 5AC antennas as a 650m radio bridge.

Today I encountered a link loss, it turned out that bridge side detected radar, but it didn’t seem to be able to switch frequencies (if I uderstand this correctly?)

Can you take a look on the log?

1:09:41 wireless,info wlan1: radar detected on 5580000 
11:09:41 wireless,info B8:69:F4:61:61:7B@wlan1: disconnected, disabling 
11:09:46 wireless,debug wlan1: must select channel 
11:09:46 wireless,debug wlan1: selected channel 5660000 
11:09:46 wireless,debug wlan1: search for radars on 5660000 
11:10:37 wireless,info wlan1: radar detected on 5660000 
11:10:41 wireless,debug wlan1: must select channel 
11:10:41 wireless,debug wlan1: failed to select channel 
11:10:51 wireless,debug wlan1: must select channel 
11:10:51 wireless,debug wlan1: failed to select channel 
11:11:01 wireless,debug wlan1: must select channel 
11:11:01 wireless,debug wlan1: failed to select channel 
11:11:11 wireless,debug wlan1: must select channel 
11:11:11 wireless,debug wlan1: failed to select channel 
11:11:21 wireless,debug wlan1: must select channel 
11:11:21 wireless,debug wlan1: failed to select channel 
11:11:31 wireless,debug wlan1: must select channel 
11:11:31 wireless,debug wlan1: failed to select channel 
11:11:41 wireless,debug wlan1: must select channel 
11:11:41 wireless,debug wlan1: failed to select channel 
11:11:51 wireless,debug wlan1: must select channel 
11:11:51 wireless,debug wlan1: failed to select channel 
11:12:01 wireless,debug wlan1: must select channel 
11:12:01 wireless,debug wlan1: failed to select channel 
11:12:11 wireless,debug wlan1: must select channel 
11:12:11 wireless,debug wlan1: failed to select channel 
11:12:21 wireless,debug wlan1: must select channel 
11:12:21 wireless,debug wlan1: failed to select channel 
11:12:31 wireless,debug wlan1: must select channel 
11:12:31 wireless,debug wlan1: failed to select channel 
11:12:41 wireless,debug wlan1: must select channel

I would expect to select new channel, test for radars, eventually either bring it up or detect radar again and select a new one…
But I see that it fails to select, can you advise what might be a reason?

2

Do you have some frequency list set on AP side?

After wlan device detects radar on a frequency channel, that channel is banned from use for quite some time (minutes). If all frequency channels configured are banned, then … well, link can’t reestablish.

3

I don’t think so (I don’t even know where to set the frequency list) - however my frequency was set to manual, and it seem it did try (once) to switch → from set 5580 to 5660.

4

If frequencies are manually set, it will be visible in /interface wireless export … attribute frequency … if device is set to auto-select frequency, it’ll show frequency=auto … if frequency is set manually, it will be something like frequency=5580,5660 (comma-separated frequency list).

5

Even if you set manually to one frequency, the DFS will switch to the other DFS frequencies. My systems do this correctly.

But besides a channels list on the interface, that is not used I understand, so its the default list, there is no further information.
What is the bandwidth used 80MHz, 40MHz, 80+80MHz ??? This will limit the potential usable frequencies.
Regulatory domain region or country may also limit the possible candidates.

You already “lost” two candidates 5580 and 5660 for “x” minutes (have to look it up for how long), depending on the channel width you can know what channels are lost for immediate use.
For 80MHz bandwidth, then 5500 is the only other DFS possibility. (US/FCC still has UNII-3 as non-DFS) . But maybe that one is just a bit earlier in the log.
5500 with 80 MHz is the only one with 1 minute delay before activation, the others are 10 minutes. And 5660 (Ceee) on 80MHz is tricky in a large part of the world, as channel 144 is not allowed.

DFS cannot be disabled. I see bridge and station-bridge (?) in your LHG5ac link. So it’s PtP ? One trick is to switch the function bridge and station, you will be looking in the other direction for radars.

In my case an hAP ac2 at 5180MHz generated false possitive radar detects on 5540, when set at a higher frequency the false radar detect moved up in frequency as well.
So be careful with other AP’s in the beam of the “bridge” or “AP bridge”.

Just FYI, this is my personal list for DFS channels, avoiding 10 minutes outages unless it’s the only option. The manual entered frequency will be the starting point in the list.
But it will not solve your radar detect problem however.
Klembord-2.jpg