To do some broadcasting is a strain (3)
I believe the answer is:
air
'a strain' is the definition.
(I know that strain can be written as air)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for air that I've seen before include "Region above the ground" , "Mix of gases surrounding the earth" , "Skye Boat Song, perhaps" , "If it's hot, it's boastful" , "Ventilate a tune?" .)