It's heard on radio: 'In California, 50 N American soldiers rising' (4,4)
I believe the answer is:
call sign
'it's heard on radio' is the definition.
I know that 'radio' relates to this answer.
'california 50 n american soldiers rising' is the wordplay.
'california' becomes 'cal' (short for California).
'50' becomes 'L' (roman numeral).
'american soldiers' becomes 'gis'.
'rising' says the letters should be written in reverse (going up in a down clue).
'n'+'gis'='ngis'
'ngis' in reverse letter order is 'sign'.
'cal'+'l'+'sign'='CALL SIGN'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for call sign that I've seen before include "Radio station or aircraft identifier" , "Radio identification" , "Identifying code of sender or receiver of broadcast message" , "A wireless operator's identification" , "Unique designation in radio communications" .)