The radio station uses the dweller's Charisma to send broadcasts into the wasteland in order to attract new dwellers. However, sometimes it may do nothing at all or even attract raiders and deathclaws. This room also helps raise happiness among vault dwellers. The happiness bonus appears to be a one-time bonus applied when a dweller is assigned to the room. The bonus is removed when the dweller is removed from the radio station. This room requires 20 dwellers to unlock. One update added the ability to toggle between broadcasting to the wasteland or just within the vault. This allows you to still get the happiness bonus without attracting new dwellers, raiders or deathclaws.