CABLE TELEVISION FACT SHEET CABLE CARRIAGE OF BROADCAST STATIONS
Q: Why must my cable system carry so many broadcast stations?
A: The Communications Act requires cable operators to set aside a specified portion of their channels for local commercial and non-commercial television stations. A cable operator with 12 or fewer channels must set aside up to three channels for local commercial television stations and at least one channel for a local noncommercial educational television broadcast station. Cable operators with more than 12 channels must set aside one third of their channel capacity for local commercial stations. Cable systems with between 13 and 36 channels must carry at least one, but need not carry more than three, local noncommercial educational television stations. Cable systems with more than 36 channels must carry all local noncommercial educational television stations requesting carriage with some exceptions for duplication of signals. Local television stations choosing the must-carry option and those that have negotiated agreements for retransmission with the cable system count towards this quota.
http://www.fcc.gov/mb/facts/cblbdcst.html