Complex sentence: There was no over-the-air competition until August 18,2007, when NBC affiliate WDTN began to produce a nightly 10 o'clock newscast on CW affiliate WBDT; this beat WRGT's show in Dayton's metered market household ratings on the 26th day of its broadcast.
Split into simpler sentences: There was no over-the-air competition to the nightly broadcast until August 18,2007 when NBC affiliate WDTN began to produce a nightly 10 o'clock newscast on CW affiliate WBDT. This beat WRGT's show in Dayton's metered market household ratings on the 26th day of its broadcast.