Shutting down power to radar dishes is part of the Week 14 legendary quests in Fortnite Chapter 2 Season 7, which, if you want the XP, must be completed before the end of the season.
Completing this challenge will reward you with 30k XP, which will help you unlock more Battle Stars for the Season 7 Battle Pass. You'll also be able to complete the next legendary quest - spoil the Mole's sabotage attempt.
Note this particular challenge is no longer able to be completed. So what's new since? Check out the Fortnite Chapter 3 Battle Pass skins, the new Fortnite map and the Victory Umbrella. You can also now slide!
Radar dishes locations in Fortnite explained
You need to shut down two of the seven radar dishes located on the Fortnite map and each radar dish can be found within the IO bases.
Once you've decided which bases you wish to visit for this legendary quest, you need to head to the base of the radar dish. There you'll find a small power box, which, once interacted with, will shut down the power for that radar dish.
Remember - you need to shut down the power for two radar dishes to complete this challenge, which means you need to visit two IO bases. For this reason, if you want to complete this quest in one match, it's a good idea to visit the Weeping Woods and Slurpy Swamp bases, since they're close to each other.