<P> In the United States , for most of the history of broadcasting , there were only three or four major commercial national broadcast networks . From 1946 to 1956 , these were ABC , CBS , NBC and DuMont ( though the Paramount Television Network had some limited success during these years ) . From 1956 to 1986 , the `` Big Three '' national commercial networks were ABC , CBS , and NBC ( with a few limited attempts to challenge them , such as National Telefilm Associates ( and its NTA Film Network ) and the Overmyer Network ) . From 1954 to 1970 , National Educational Television was the national clearinghouse for public TV programming ; the Public Broadcasting Service ( PBS ) succeeded it in 1970 . </P>
<P> In the United States , for most of the history of broadcasting , there were only three or four major commercial national broadcast networks . From 1946 to 1956 , these were ABC , CBS , NBC and DuMont ( though the Paramount Television Network had some limited success during these years ) . From 1956 to 1986 , the `` Big Three '' national commercial networks were ABC , CBS , and NBC ( with a few limited attempts to challenge them , such as National Telefilm Associates ( and its NTA Film Network ) and the Overmyer Network ) . From 1954 to 1970 , National Educational Television was the national clearinghouse for public TV programming ; the Public Broadcasting Service ( PBS ) succeeded it in 1970 . </P>
when does the us open air on tv
when does the us open air on tv
1954
1954