How do you minimize signal interference for telecommunication? Easy: Take a wire that acts as an inner conductor and wrap an outer conductor around it, instead of running two wires side by side. That way, the electromagnetic field carrying the signal will only travel in the space between the inner and outer conductors. That will allow wider frequency range, too.
That invention — known today as the coaxial cable, because the two conductors share the same axis — wasn’t realized in the United States until 1931. Experiments with co-ax cables took place in Bell Laboratories for possible telephone usage. Each cable route, consisting of several individual cables, could carry 1,800 calls.
U.S. Patent No. 1,835,031 for a “concentric conducting system” was awarded to Lloyd Espenschied of Kew Gardens, New York, and Herman A. Affel of Ridgewood, New Jersey, and assigned to the American Telephone & Telegraph Co.
Coaxial cable technology improved over time to increase capacity. By the 1970s, systems could support up to 132,000 conversations.