同轴电缆
In 1937 RCA raised the frame definition to 441 lines, and its executives petitioned the FCC for approval of the standard. By June 1939, regularly scheduled 441-line electronic television broadcasts were available in New York City and Los Angeles, and by November on General Electric's station in Schenectady. From May through December 1939, the New York City NBC station (W2XBS) of RCA broadcast twenty to fifty-eight hours of programming per month, Wednesday through Sunday of each week. The programming was 33% news, 29% drama, and 17% educational programming, with an estimated 2,000 receiving sets by the end of the year, and an estimated audience of five to eight thousand. A remote truck could cover outdoor events from up to away from the transmitter, which was located atop the Empire State Building. Coaxial cable was used to cover events at Madison Square Garden. The coverage area for reliable reception was a radius of 40 to from the Empire State Building, an area populated by more than 10,000,000 people (Lohr, 1940).