If you slice through the snake of black cable that connects to your TV set and peer directly into the exposed innards, you’ll see a circle. Inside it, at the center, is a conductor, which in turn is shielded by insulating material and surrounded by a concentric outer conductor. You’re staring at an essential enabler of the modern telecommunications revolution: coaxial cable.
This fundamental medium for transmitting signals via radio frequencies has been around a long time, even well before an engineer named Edward Parsons strung lines of coax between a transmitting antenna and houses in Astoria, Ore., to launch the cable television industry in the late 1940s.
Its origins, if you indulge in a permissive definition of coax, actually trace all the way back to the mid-1800s, when engineers laid cables, shielded with latex derived from Malaysian Gutta Percha trees, across the Atlantic Ocean to transmit telephone and telegraph signals. As the ham radio historian Gil McElroy explained in a 2001 paper on the origins of coax, these cables were considered “coaxial” – meaning they shared a geometric common axis – “because the seawater that surrounded them completed their return circuits.” The first patent for a coaxial cable system was awarded in England, in 1880, to the electrical engineer Oliver Heaviside.
The modern incarnation of coaxial cable, though, was conceived in 1929, when two AT&T inventors filed a patent application for a coaxial cable system that could accommodate television signals by exploiting a wider range of frequencies than anyone had managed before. The applicants, Lloyd Espenschied and H.A. Affel, received U.S. Patent No. 1,835,031 in December 1931. The patent application describes an essential and enduring attraction of coaxial cable, which is its ability to contain energy: “The concentric arrangement not only has the advantage that it produces substantially no external interfere[nce] in other circuits, but it is practically free from interference due to any external source,” the authors wrote.
Their invention got its first trial run in 1936 when a dual-cable underground coax network was installed between New York City and Philadelphia to transmit voice and telegraph signals. The next year, the same system carried live broadcasts of the 1940 Republican National Convention to viewers in New York, and what would be a decades-long marriage between television and coax was under way. When Parsons and peers in Pennsylvania began using coax to extend the reach of broadcast TV signals in rural areas, the prevailing name for their creation was Community Antenna Television, or CATV, but it didn’t take long for the simpler term “cable TV” to come to the forefront.
Ever since, coaxial cable has lived on as the reliable workhorse of the pay TV industry, surviving generational changes in architecture that saw the deployment of 450 MHz amplifiers, the construction of dual-cable systems, the introduction of fiber optics and, eventually, the industry’s adoption of HFC, the hybrid fiber-coax network topology that powers most of the cable industry today.
How long can coax continue to reign? With fiber-to-the-home networks rising in prominence, there’s pressure building to replace the last-mile connections supplied by amplified coax networks with powerful, high-capacity optical networks.
According to the latest statistics published by the Organisation for Economic Development and Cooperation, FTTH networks accounted for roughly 16 percent of the world’s fixed-line broadband connections as of June 2013, up from 13.9 percent a year earlier.
But coax doesn’t appear to be done just yet. Emerging techniques for wringing more bandwidth out of hybrid networks, including DOCSIS 3.1, wrinkles like the adoption of orthogonal frequency division multiplexing, and advanced error correction techniques, are built to coax (pun fully intended) more capacity from existing HFC networks. Some industry technologists believe HFC can adequately accommodate projected bandwidth demands through the remainder of the decade and possibly longer.
All of this could change, and suddenly, if the best-laid plans are upended by dramatic increases in bandwidth spawned by technologies we don’t even know about yet, or by an unexpected surge in demand as the so-called Internet of Things manifests itself in the home with more force than anticipated. But for now, it appears as if a fundamental component of the telecommunications revolution will remain firmly entrenched. Coaxial cable has shown remarkable resiliency as a conduit for entertainment, information and communications since it was first implemented commercially more than 70 years ago. It’s difficult to think of another technology that has a similar record for longevity. For coaxial cable, the circle really has remained unbroken.