Broadcaster in South American city screening commercial (5)
I believe the answer is:
radio
'broadcaster' is the definition.
(radios broadcast signals)
'south american city screening commercial' is the wordplay.
'south american city' becomes 'rio' (Rio de Janeiro in Brazil).
'screening' indicates putting letters inside (inserted letters are covered or screened by others).
'commercial' becomes 'ad' (abbreviation for advertisement).
'rio' placed around 'ad' is 'RADIO'.
'in' is the link.
(Other definitions for radio that I've seen before include "Speech receiver" , "Communications receiver" , "means of communication" , "Receiving device" , "MW, LW or FM sound source" .)