In several countries like European countries, channels 120, 124 and 128 are allowed for outdoor usage.
You may nevertheless have noticed that these channels are locked, they are per default even not scanned when a device is configured as AP.
The reason is simple:
These channels are "weather channles" where weather radars may be used. The EN 301 893 defines 10 minutes of Channel Availability Check (CAC) for the weather channels instead of only 1 for the other channels of the sub-band.
It means that before to use one of these channels, an AP will perform 10 min scanning in the channel.
Due to this reason, these channels are per default disabled to privilege the use of the non weather channels.
It's nevertheless possible to enable them either per CLI or via the web interface. But be aware that their usage may lead to longer CAC.
set Setup/WLAN/DFS/Use-Full-Channelset yes
HiLCOL Menu Tree > Setup > WLAN > DFS > Use-Full-Channel-Set