Concerned with betting on the German signal receiver (9)
I believe the answer is:
responder
'signal receiver' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'concerned with betting on the german' is the wordplay.
'concerned with' becomes 're' (re can mean regarding, concerning).
'betting' becomes 'sp'.
'the german' becomes 'der' ('the' in German).
're'+'sp'+'on'+'der'='RESPONDER'
Can you help me to learn more?
(Other definitions for responder that I've seen before include "Reactor" , "one giving a reaction" , "one should give a reply" , "One replying or reacting" , "provides one with the answer" .)