Broadcast on fine trade show (4)
I believe the answer is:
fair
'trade show' is the definition.
(I've seen this before)
'broadcast on fine' is the wordplay.
'broadcast' becomes 'air' ('air' can be a synonym of 'broadcast').
'on' is a charade indicator (letters next to each other).
'fine' becomes 'f' (abbreviation).
'air' put after 'f' is 'FAIR'.
(Other definitions for fair that I've seen before include "... enough! - that's reasonable" , "Just; fete" , "clean" , "Beautiful; exhibition" , "Women are known as the ... sex" .)