Roller base for radio transmission (4-4)

'transmission' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I don't see?

'roller base for radio' is the wordplay.
'roller' becomes 'wave' (I've seen this in another clue).
'base for' is a charade indicator (letters next to each other) (some letters act as a base underneath others).
'radio' becomes 'long' (I can't explain this - if you can you should give a lot more credence to this answer).
'wave' after 'long' is 'LONG-WAVE'.

Can you help me to learn more?