By the early 1920s, AT&T engineers recognized that the open wire and cable in use at the time would be unable to carry the high frequencies needed for the broadband systems of the future. So Espenschied and Affel developed a new kind of wire system that could transmit a continuous range of high frequencies over long distances.
This revolutionary transmission system was based on the use of a coaxial conductor: two concentric cylinders of conducting material separated mainly by air. This structure reduced frequency losses and provided freedom from outside interference.
Espenschied and Affel were granted a patent in 1931. And in November 1936, the first voice transmission was made over coaxial cable installed between New York and Philadelphia.
The introduction of broadband coaxial cable made possible not only higher-capacity long distance circuits, but also intercity transmission of moving images, which paved the way for television.