Boom coming from radio transmitter (4)
I believe the answer is:
mast
This clue is a double definition.
'boom' is the first definition.
(thesaurus)
'radio transmitter' is the second definition.
(I know that mast is a type of radio transmitter)
'coming from' is the link.
(Other definitions for mast that I've seen before include "Spar to support a sail" , "it rises on board a ship" , "food for pigs" , "Pole on ship" , "One carries the sails of a ship" .)