Broadcasting in Bulgarian, old revolutionary (2,3)
I believe the answer is:
on air
'broadcasting' is the definition.
(broadcasting on the air)
'in bulgarian old revolutionary' is the wordplay.
'in' says the answer is hidden in the clue.
'revolutionary' says the letters should be written backwards (letters revolve around).
'riano' is hidden within 'bulgarian old'.
'riano' written backwards gives 'ON-AIR'.
(Other definitions for on air that I've seen before include "Radio show might be" , "Transmitting now!" , "In the process of broadcasting on radio or TV" , "with audience?" , "If you're really happy, you'll float here" .)