With effort, release old period broadcast (5)

I believe the answer is:

expel

I'm a little stuck... Click here to teach me more about this clue!

'release old period broadcast' is the definition.
'expel' can be an answer for 'release' (synonyms). I am not sure about the 'old period broadcast' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for expel that I've seen before include "bar" , "Deport" , "Drive out with force" , "Possibly remove from club" , "Banish (undesirable alien?)" .)

I've seen this clue in The Times and The Sunday Times.

Want a hint initially instead of a full solution? Install my app