How to Extend a Coaxial Cable Line

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How to split and extend coaxial cable for adding another television or cable modem in your home.

When cable was initially run to homes in the United States only one cable jack was normally installed. As time went on, people often added more televisions that required additional jacks. If you need another jack for a cable TV signal; set up a computer network in your home; or hook up an FM radio or a cable modem chances are you'll be working with coaxial cable. Coaxial cable, often referred to as "coax," is a round black cable that cable companies run from the street to your cable box. Chances are you already have coax in your house.

This article will illustrate how to work with coax and describe how to make a couple of essential coax connections.

About Coax

Coax consists of a center wire surrounded by insulation, which is in turn surrounded by an outer conductor of braided wire that serves as a grounded shield, enclosed in an outer jacket of insulation. The shield minimizes electrical and radio frequency interference. There may also be a layer of foil between the interior insulation and the outer conductor.

Coaxial Cable

Coax gets its name because its two channels run concentrically along the same axis. It is old technology that was originally designed to carry analog telephone signals at high capacity with little electronic noise. Coax is virtually weatherproof and much more durable than "twinlead" wire that is the flat wire originally used for TV antennas. Signal performance is also superior. Coax doesn't pick up unwanted signals, and it's not affected by contact with metal structures. And although cable installers often use special standoff supports when attaching coax to exteriors, all you need to route coax inside your house are coaxial cable clips.

Coaxial cable is easy to work with as long as you have a few tools. Tapping into an existing coaxial line to hook up a second TV or extend a computer network is known as "splitting.” Standard tools are fine for making a couple of connections, but if you're making a lot of them, invest in a few inexpensive specialized tools: the work will be faster and more professional. If you're hooking up more than one additional unit, buy a splitter with three or four outputs, or terminals, instead of two. This usually yields better results than splitting the line at each device, which may weaken the signal.

The more splitters you add, or the more ports on the splitters will result is signal loss. Splitters have the loss stated on them, usually between -1 dB and -3.5dB for 2-way splitters and up to -11dB for 8-way splitters. If you have poor signal quality at the end of your last run, you may need to install an amplifier after the splitter to boost the signal strength. See the illustration below. Check you equipment to determine what the maximum allowable loss in signal strength is.

Example of Video Signal Losses

Tools and Supplies:



Spade bit set

Four 1 1/4-inch drywall screws

Lineman's pliers

Two-way, 75-ohm line splitter

Coaxial cable

Coaxial cable stripper/crimper or utility knife

Coaxial cable straps

Two F-plugs

Splitting and Extending a Line

To split and extend a cable from one TV that is connected to a coax line, unscrew the screw-on connector from the back of the TV. Mount the splitter to a baseboard or similar location with the mounting screws provided, or use 1 1/4-inch drywall screws. Be sure to mount the splitter within reach of the original coax line. Screw the original connector into the tap marked "input" on the splitter.


Next, you'll need two new coaxial cables, one for the original device and one for the new device. You can either buy them with connectors already attached or make a new one of the appropriate length. Screw one end of each new cable to an output tap on the splitter and the other end into the input jack on the back of the TV or other device.

Support the cable between the splitter and the devices with coaxial cable clips nailed to baseboards every 2 or 3 feet. If you need to run cable through interior walls, drill passage holes in corners or other inconspicuous locations using a spade bit. You can run cable through exterior walls almost the same way. To keep water out of your walls, always make a drip loop where the cable enters your home, as shown above. Be sure to seal the exterior hole with silicone caulk.

Attaching a Coaxial Cable Connector

You can purchase coaxial cable at hardware stores, home centers, or electronic stores that will allow you to fabricate cables to the exact length of your run. Excessively long cables will reduce signal quality, expressed in –dB.

Coaxial cable connects to electrical equipment with F-plugs, which clamp onto the stripped cable and screw or slide onto the device or splitter. If you're adding a new cable, you will need F-plugs on both ends.

To put an F-plug onto a length of coax, cut the cable's end square with lineman's pliers. Then use a coaxial cable stripper or a utility knife carefully to remove 1/2 inch of the cable's outer covering and peel back the woven outer conductor and foil, folding it back over the outer insulation. Second, strip 1/4 inch of the inner insulation to expose the copper conductor. To attach the connector, first slip its ferrule onto the cable. Then push the body of the connector over the white insulation, fitting the sleeve under the outer conductor and foil. The white insulation will bottom out in the connector, and the inner conductor will protrude through the hole in the end of the plug. Finally, crimp the ferrule with a coaxial cable crimper or pliers to hold the connector in place.

For about $5 you can buy a cable stripping tools that has 2 blades, one is set to strip the out black insulation and the other will cut away the inner white insulation.

For a more finished installation you can run the cable inside the wall and install a cover plate with a male cable fitting already installed. You can run the cable behind baseboard or use attic of basement spaces to run the cable unobstructed. You will only need to cut one hole in the wall and install an old-work electrical box, or low-voltage open box to attach the face plate to.

Low-Voltage Open Box

Hopefully you will be able to extend or add coaxial cable jacks in your home that will provide more flexibility to your electronic and home entertainment systems.