Radio Freedom

Radio Freedom is a radio signal in The Commonwealth in Fallout 4.

Radio Freedom is a radio station based from The Castle settlement after reclaiming it for the Minutemen. The radio will broadcast violin music, as well as alerts for Minutemen-related problems and sometimes give quests for the player to complete.

Bugs
If The Castle is attacked, or the Settler Bell is rung within its boundaries, the Minuteman who hosts Radio Freedom will leave his post, then refuse to return to it. This will disable Radio Freedom, as well as artillery. There are no fixes available on the Xbox One or PS4. Bethesda knows of this bug, and has classified it as a major bugs.

(Requires further testing - on PS4, this bug appears to be fixed by storing the wire, connecting the power to the radio station, in the workshop and then re-attaching it. The music can be heard playing again and the NPC stationed at the radio desk returns to their seat. After enabling the radio on the pip-boy the normal functions are returned and the sole survivor can again receive quests, use artillery and enjoy the violins.)

For those who own the PC version, a solution can be found at http://www.nexusmods.com/fallout4/mods/5169/?. Once you have downloaded the file, follow the "read me" instructions. After you enter the console commands, attempt to assign any settler and the original broadcaster will return to his chair.