Complex sentence: On September 16,1988, the station changed its call letters to the current KNSD, and began calling itself "Channel 7/39" (in reference to both its cable and over-the-air channel positions) on-air.
Split into simpler sentences: On September 16,1988, the station changed its call letters to the current KNSD. It also began calling itself "Channel 7/39" on-air.