gener ally , ▁fewer ▁than ▁five ), ▁affili ation ▁agre ements ▁are ▁usually ▁exclusive : ▁for ▁example , ▁if ▁a ▁station ▁is ▁affili ated ▁with ▁N BC , ▁it ▁consequ ently ▁would ▁not ▁air ▁programs ▁from ▁ABC , ▁CBS ▁or ▁other ▁conventional ▁broadcast ▁networks ▁but ▁may ▁carry ▁special ty ▁services ▁intended ▁to ▁be ▁carried ▁on ▁digital ▁television ▁signals ▁on ▁one ▁or ▁more ▁sub ch annels . ▁ ▁Arr ang ements ▁in ▁which ▁television ▁stations ▁carried ▁more ▁than ▁one ▁network ▁on ▁its ▁main ▁signal ▁( which ▁often ▁resulted ▁in ▁some ▁network ▁programs ▁being ▁not ▁being ▁cleared ▁to ▁air ▁locally ▁by ▁the ▁station , ▁thereby ▁limit ing ▁their ▁national ▁carriage ▁and ▁resulting ▁in ▁view ers ▁having ▁to ▁rely ▁on ▁an ▁out - of - market ▁station ▁rece iv able ▁in ▁their ▁area ▁that ▁air s ▁the ▁locally ▁pre - empt ed ▁show ▁through ▁an ▁affili ation ▁with ▁that ▁same ▁network ▁in ▁order ▁to ▁see ▁it ) ▁were ▁more ▁common ▁between ▁the ▁ 1 9 4 0 s ▁and ▁the ▁ 1 9 6 0 s , ▁although ▁some ▁arrang ements ▁continued ▁as ▁late ▁as ▁ 2 0 1 0 . ▁Today , ▁programming ▁from ▁networks ▁other ▁than ▁that ▁with ▁which ▁the ▁station ▁maintain s ▁a ▁primary ▁affili ation ▁are ▁usually ▁carried ▁over ▁digital ▁sub ch annels , ▁which ▁increasing ly ▁since ▁the ▁mid - 2 0 0 0 s , ▁have ▁allowed ▁one ▁of ▁the ▁major ▁broadcast ▁networks ▁to ▁expand ▁their ▁national ▁coverage ▁to ▁mark ets ▁where ▁they ▁would ▁have ▁previously ▁either ▁had ▁to ▁sett