Obscurity not observed in radio broadcast (4)
I believe the answer is:
mist
'obscurity' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for mist that I've seen before include "Fine spray" , "Thin layer of fog" , "Watery film" , "Think fog or low cloud" , "low-level cloud" .)