user: Question: What is the purpose for the Katherine freq of 8RN?
Columns: ['Callsign', 'Area served', 'Frequency', 'Band', 'Freq currently', 'Purpose']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['5AL', 'Alice Springs', '1530', 'AM', '8AL (783 kHz)', 'National']
SQL:

assistant: SELECT "Purpose" FROM "Table" WHERE "Freq currently" = '8RN' AND "Area served" = 'Katherine';