Frank and Darleen, what you are referring to was (and still is) affectionately known as "dual cable plant". Several municipalities around the country still run this configuration while preparing for HFC upgrades, as Frank has properly stated.
It actually consists of 2 physical cables placed in the same ROW to distribute signals to homes. Most of these systems were put in place in the mid to late 70's, very early 80's to ward off the complaint from subscribers that they couldn't get more channels. It allowed a person to switch between the "A" and the "B" channels to receive more channels on their cable service. If you look closely at some old settop boxes and settop remote controls you can actually see an A and a B labeled on their and this was how you switched between cables. Channel lineups were printed showing which channels were on the A cable and which were on B channel.
Why do this, you ask. Simple, because in the early days of cable these systems were built typically as 330 MHz or less bandwidth which would usually support 20 to 25 channels or less. So if you wanted more, you needed a way to either upgrade to higher bandwidth (in those days upgrades to higher bandwidth cost big bucks) or put in a second cable and processors for the added channels. A side benefit of the second cable was that it typically wasn't loaded up with channels which let an operator play with new stuff. As an example, in Cincinnati, not only do they have a weak football team, they also have the remnants of one of the earliest interactive TV systems known as QUBE. This interactivity was enabled by having enough bandwidth to play with via the dual cable plant.
All modern HFC networks, built to 550 MHz, 750 MHz or 860MHz do not need the second cable because they have plenty of bandwidth available to handle analog and digital TV, cable phone, high speed data, PPV, etc. with fiber and a single coax to the home. There are even some 1GHz systems out there operating today.
Hope that helps and was fun. I don't usually get to play historian, so some of the details might be slightly off, but I think you get the idea. |
