The station originally broadcast on UHF channel 20 on a transmitter originally used for WWLP's partial satellite, WRLP-TV in Greenfield, Massachusetts, which closed down shortly before KSTU's sign-on. KSTU's programming at the time was typical for an independent station: cartoons, off-network sitcoms, classic movies, and drama series. Springfield Television merged with Adams Communications in 1984. On October 9, 1986, the station became a charter affiliate of Fox. However, like most Fox affiliates early in the network's history, it was still essentially programmed as an independent. Fox initially ran only late-night programming at its launch and when it added primetime programming in April 1987, it only aired such programs on Saturdays and Sundays. It would not air a full week's worth of programming until 1993.