▁limit ▁to ▁un wind ▁existing ▁JS As ▁to ▁ten ▁years ). ▁ ▁The ▁F CC ▁also ▁previously ▁bar red ▁companies ▁from ▁ow ning ▁more ▁than ▁one ▁television ▁station ▁within ▁a ▁single ▁market , ▁unless ▁it ▁operated ▁as ▁a ▁satellite ▁station ▁( a ▁full - power ▁station ▁that ▁rel ays ▁programming ▁from ▁its ▁parent ▁station ▁to ▁areas ▁within ▁the ▁market ▁that ▁are ▁not ▁ade qu ately ▁covered ▁if ▁at ▁all ▁by ▁the ▁main ▁signal ) ▁or ▁a ▁low - power ▁station ▁( e ither ▁one ▁that ▁maintain s ▁its ▁own ▁programming ▁or ▁oper ates ▁as ▁a ▁transl ator ); ▁however , ▁it ▁eventually ▁allowed ▁operators ▁of ▁public ▁television ▁stations ▁to ▁sign - on ▁or ▁ac quire ▁a ▁second ▁station ▁that ▁did ▁not ▁repeat ▁the ▁parent ' s ▁signal ▁( some ▁of ▁which ▁were ▁originally ▁lic ensed ▁as ▁commercial ▁out lets ). ▁In ▁August ▁ 1 9 9 9 , ▁the ▁F CC ▁legal ized ▁the ▁common ▁ownership ▁of ▁two ▁commercial ▁stations , ▁known ▁as ▁du opol ies , ▁if ▁one ▁of ▁them ▁is ▁not ▁among ▁the ▁market ' s ▁four ▁highest - r ated , ▁and ▁if ▁there ▁are ▁at ▁least ▁eight ▁companies ▁that ▁each ▁own ▁full - power ▁stations ▁within ▁the ▁market . ▁While ▁the ▁parent ▁companies ▁of ▁N BC , ▁ABC , ▁CBS ▁and ▁Fox ▁are ▁not ▁prohib ited ▁from ▁ow ning ▁a ▁second ▁broadcast ▁network ▁( and ▁all ▁of ▁them , ▁except ▁for ▁ABC , ▁are ▁co - owned ▁with ▁one ), ▁an ▁F CC ▁law ▁known ▁as ▁the ▁" du