The radio station transmits a broadcast into the wasteland in order to attract new dwellers. If the room is poorly managed, however, it may do nothing at all, or it may even attract raiders and deathclaws. Its overall effectiveness is based on the assigned dwellers' Charisma.
This room also helps raise happiness among vault dwellers. The happiness bonus endures while a dweller is assigned to the room and is removed when once all dwellers have been unassigned. The room also features 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. Any dwellers assigned to the room will have their happiness raised slowly over time (as there is no rush option for the room).