Shared Knowledge
“CATV House Wiring”
26 September 2005
It is hard to believe now that once upon a time, most people got their television signals from an outside antenna. I remember reading some 40 years ago in the “Mechanics Illustrated” magazine (wonder if “Illustrated” is still published?) that one day, most people would receive various information to include their television shows over a cable, which was run into their house from the street. At the time, this concept, idea, future prediction, did not make any sense to me as why would someone would pay for a cable service when they could just continue to use an antenna and receive various broadcasts for free. Wrong, once again. Today, Community Antenna Television (CATV) is in over 69.8% of all American households having a television set.
How the CATV (cable) is actually configured or wired for a house varies from home to home, depending on whether or not the house was built before or after the neighborhood was wired for CATV. Although CATV has actually been around for a long time, only in the last 15 years or so has it become widely available and thus for most homes, CATV is an add-on and exists of a cable coming to the home from the street where it probably is connected to a “splitter” from which one or more cables are then run along the outside of the house, to where the homeowner defined he or she wanted access (known as a “drop”) to the cable. At this point or points, the cable is routed through the house wall and finally terminated in a wall fixture CATV wall plate. I would be willing to bet that most older homes only have 2 CATV drops although with more and more households moving to cable Internet, 3 drops may become more the norm.
If you live in a house with 1,2 or 3 drops, there is not much you really need to know about CATV wiring except the following:
- Unlike electrical wiring, you cannot simply route a CATV cable to one drop and then continue the same cable to another drop. You must use what is known as a splitter.
- If the cable from the street is tied into a splitter outside your home, make sure that there is a wire from the case of the splitter to earth ground. This will give you some level of protection if the CATV system is hit by lightening. Also, any splitter outside the house should actually be mounted to the house with screws or brick nails. Finally, if possible, make a loop of the cable coming from the street before it connects to the first splitter as this will serve as a rainwater drip path and keep water out of the splitter.
- Always keep the number of cable splices (connectors or barrel pass-through) or splitters to a minimum. Every splice or splitter drops the cable signal strength. For example, it is better to run 3 separate cables from a single splitter than run a single cable and then insert a splitter and on the cable coming off the splitter, still another splitter.
- If you have several drops but are not using them all, you should buy what is known as cable terminators and install a terminator on all unused cable drops. An open, meaning not terminated, CATV cable drop, allows the CATV signal to bounce up and down the cable inducing interference in the entire cable system. Installing a cable terminator ends signal bounce.
- If a splitter has unused cable connections, you should install a terminator on them, like any unused cable drop.
- Always use the best quality splitters you can find. I recommend the ones sold for use in a dish-based system, which handles frequencies up to 1000MHZ or higher.
- If you have to add a drop, I suggest you use screw-on cable connectors or buy a cable already set up with a connector at either end. There are other types of connectors on the market to include crimp on but I have never had much luck with getting them tight on the end of the cable. Getting the screw-on type connector just right on the end of the cable, can take a time or 2 as determining how much insulation to cut back and how long to leave the center wire can be tricky at first. Any cable with a connector on it used outside should have a rubber boot around the connector to keep the weather out of it. It is amazing how quickly electrical connections can corrode when left to the elements. AND.... never run a CATV cable along side (parallel) any sort of house electrical cable (120 or 240V). The house current cable will induce interference into the CATV cable. If at all possible keep power and CATV cables separated by feet.
- If you want to add a signal booster to your CATV system, add it as close to the street side of the CATV as possible and if you are using the cable as your Internet connection or plan to in the future, make sure you buy a bi-directional cable amplifier.
- If you have to add a cable drop, you can buy plastic electrical outlet boxes at your local hardware store, which easily install into drywall because they have these plastic wings on them that screw down into place and tighten against the backside of the drywall. These plastic boxes come either in full depth or shallow wall varieties, so, you route the cable along the outside of your house to where you need a drop, attach the cable to the house with cable nails or other suitable, drill through the wall of the house and route the cable into the hole. You then caulk to seal around where the cable penetrated the house wall. Finally, you determine where you want your drop, using the plastic outlet box, mark an outline on the wall, and then cut out a rectangular hole using a box cutter or other tool. With the outlet hole in place, you route the cable through the plastic box and then insert the box into the hole and take a screwdriver to the 2 screws provided on either side of the plastic box, which brings plastic wings down into place and are gradually tightened on the backside of the drywall and you screw them. You then install a connector on the CATV cable, connect it to the CATV wall plate, and screw your CATV wall plate into position.
If you live in a newer home, it is possible that many drops were installed in the house, with all CATV internal cables routed to where the CATV comes into the house. All CATV drop cables may or may not be tied to the street CATV through splitters and in my case, they were not.
Below I show the CATV distribution system I constructed for my home. In my case, when our home was renovated, CATV required a pair of wires with the set top box decoding various frequencies on the cables and presenting them as discrete cable channels. But several years ago, our local cable company went to digital cable and now only one cable of the pair of cables coming into our home is actually carrying a signal. Unlike the typical home, having only 1,2 or 3 cable drops, in my home, I have 12 cable drops and as I said, after house renovation, although all cable drop cables terminated in or near the location where the CATV company cable entered our home, none of the drops were actually attached to the cable company CATV cable.
Although it might look complex, my CATV distribution system really is not. Basically, the cable company CATV cable comes to a point at one corner of my home where it goes into a connector with an earth ground wire (not a splitter) and is then routed through the wall of my home into my utility room where it is routed to a bi-directional signal amplifier and then 3 outputs of the amplifier are routed to cable splitters to which internal house drops are attached. 1 output of the signal amplifier is routed back out through the wall and continues along the outside of the house to where it penetrates the house wall and ends up as an Internet connection drop in my office.
Why amplify the cable company side of the CATV signal if there is no splitter in the line to begin with? The idea is that as each splitter reduces the signal strength, having an amplifier in the circuit before the splitter ensures the signal strength is normal after the splitter.
As I mentioned earlier, when my house was wired for CATV, a pair of cables was required and so on my distribution system, I have taken the second, unused, cable of my CATV internal cable and also routed them to splitters but in this case, tied their wire shields and center conductors to earth ground to eliminate in any possibility that interference picked up by the unused cable is transferred to the cable with the CATV signal on it. Although it is dim in my memory now, I am pretty sure that when the CATV cable was installed in our house, it sometimes was run parallel to electrical lines and thus the CATV cable could pick up 60 HZ electrical interference. Grounding the cable shield and center conductor eliminates any interference being picked up on the unused cable and transferring it to the CATV active cable.
Although not clear in the image, I have placed cable terminators on all unused splitter connections and internal to my house, all unused drops and all unused cables have terminators on them.
Why even deal with the second, unused cable of the CATV cable pair? If I or someone else wanted to, I could route a video signal at some drop into the second, unused cable and distribute it throughout my home. For example, I could route the output of a DVD player to the second cable and have it available at every drop or I could install a video camera at some location and have its output present at every video drop.
No, I did not create the CATV cable distribution system for my home immediately after I moved in. In fact, for many years, the cable company CATV cable was only routed to 2 locations through a splitter, which hung from the floor joist in my utility room. But I cannot describe to you the difference my cable distribution system has made in the quality of the cable at every drop in my house. Interference is gone and some channels, which were once lousy, are now crystal clear.
Will I ever use the second, unused cable of my CATV distribution system? Probably not, but never know. Who would have predicted the cable-based Internet and how far it has come in the last 15 years.