even if you set a dfs channel manually (editing hostapd config or cli) if you are using qualcomm/atheros or broadcomm chipsets, they will automatically move you out once it detects radar. At least with QCA/Atheros chipsets they used to have both compiletime and runtime flags to enable/disable most features (including dfs). Also, FCC fines are huge when it comes to dfs violation - as dfs spectrum is for emergency communication (military, natural disasters etc). There are radar simulators with which you can test this.