Just missing the frequency for broadcast (3)
I believe the answer is:
air
'broadcast' is the definition.
(I've seen this before)
'just missing the frequency' is the wordplay.
'just' becomes 'fair' ('fair' is associated in meaning with 'just').
'missing' indicates named letters should be taken away.
'the frequency' becomes 'f' (abbreviation e.g. FM radio).
'fair' with 'f' taken away is 'AIR'.
'for' acts as a link.
(Other definitions for air that I've seen before include "Divulge" , "Vent; atmosphere" , "'Tune, melody (3)'" , "Cool" , "Mixture of gases needed for breathing" .)