Old revolutionary father - group on the radio picked up on (9)
I believe the answer is:
overheard
'old revolutionary father group' is the definition.
The answer and definition are not the same part of speech. However, past participle verbs and adjectives sometimes mean the same thing.
'the radio picked up on' is the wordplay.
'the radio' becomes 'over' (I can't justify this - if you can you should believe this answer much more).
'picked up' becomes 'heard' (hearing is a kind of picking up).
'on' means one lot of letters go next to another.
'over'+'heard'='OVERHEARD'
'on' is the link.
Can you help me to learn more?
(Other definitions for overheard that I've seen before include "Eavesdropped on (a conversation)" , "Head rover (anag) - listened to secretly" , "Accidentally caught" .)