Perceive what's transmitted on the radio (5)
I believe the answer is:
scent
'perceive' is the definition.
(thesaurus)
'transmitted on the radio' is the wordplay.
'transmitted' becomes 'sent' (sending is a kind of transmitting).
'on the radio' shows a homophone (sound like).
'sent' is a homophone of 'SCENT'.
'what's' acts as a link.
(Other definitions for scent that I've seen before include "Distinctive smell" , "Clue" , "Pleasant odour" , "Fragrance" , "Distinctive odour" .)