The provided source material does not contain information regarding a city named Balun in Indonesia. Instead, the source describes a balun as an electrical device used to interface balanced and unbalanced lines without disturbing the impedance arrangement of either line.
A balun can take various forms and may include devices that transform impedances, though this is not required. Transformer baluns may utilize magnetic coupling, while common-mode chokes are also used as baluns by eliminating rather than rejecting common-mode signals.