In communications I understand a man (5)
I believe the answer is:
roger
This clue is a double definition.
'in communications i understand' is the first definition.
('Roger that' on a radio)
'a man' is the second definition.
(man's name)
(Other definitions for roger that I've seen before include "One like de Coverley" , "acknowledgement of message received?" , "Ackroyd" , "man, > I understand" , "Boy's name - received and understood" .)