by Jeff Fisher
Your video distribution need may be as simple as getting a decent quality cable TV hookup to each TV. Or you may be planning to have several video cameras that you want to view from any TV, and want to "share" VCRs, satellite receivers, DVDs, etc. among all the TVs in the house.
In either case, if you're going to be wiring the video distribution system in your new or remodeled home, you need to come up to speed on what it's all about and how its done. It isn't terribly difficult or complicated. In fact, I think its actually quite fun! Its pretty much a science until you get to the "tuning" part at the end.
So don't be scared. Dive in and enjoy! You can do a much better job than your electrician or local "cable guy."
- A Little History(below)
- Section 2:Prewiring a Video Distribution System
- Section 3:Installing a Video Distribution System
- Section 4:Tuning and Troubleshooting a Video Distribution System
Residential video distribution has come a long way since the days of a roof-mounted antenna connected to a TV by a length of 300 ohm twin-lead flat-cable snaking through a window screen. Back in those days just about anybody could hook up a TV. And when a home had more than one TV (which was rare) the other sets made do with rabbit ears!
Then came cable. At first the cable companies were more than happy to hook up your TVs for free, just to get your long-term business. If you had more than one TV, they just put a splitter on the side of your home. They controlled the signal level coming down the cable so if they needed more signal strength, they handled it "up at the pole."
After a while, the cable companies became the de-facto masters of video distribution and, thus, were able to charge for installations. Over the last few years, there has been a trend for the homeowner to take charge of the low-voltage wiring within the home. This trend was driven, for the most part, by the phone and cable TV companies' attempt to make installations a "profit center." When phone and cable installations got expensive enough (and sloppily done, at that) the homeowners started doing it themselves.
Today, it seems, neither the phone or cable companies care who does the installation. Which suits us just fine, because we know that we can help you do a whole lot better job than they would. All the cable company cares about (besides you paying your bill) is that you don't mess up the signal going to neighboring "drops" (in other words--don't send any signals back up the cable) and that you don't get them in trouble with the FCC by "leaking" their signals into the air.
Introduction To Video Distribution
Video distribution is all about getting a strong clear signal, of all channels (regardless of the source), to all video destinations within the home. This involves three general functions: Gathering, and in some cases creating, the signals in one area; Combining, conditioning, and amplifying the signals; And distributing the signals to their destinations.
The first thing your need to know about video distribution is that what you are really distributing is Radio Frequency (RF) signals. These signals, given the opportunity, would happily fly through the air to your TVs. But this method of video distribution is frowned upon by the FCC because they would rather let the "licensed broadcasters" handle that method of distribution. Instead, we force the RF signal to go down shielded coaxial cables. Apart from the distribution task itself, the two most important parts of creating a video distribution system are to keep your signals inside the cables, and to keep other signals out of the cables!
A single coaxial cable can carry 130, or more, standard channel frequencies. Each channel includes video and audio components. With MTS encoding, each channel can even have stereo audio.
Contrary to an RF channel, which can coexist on a coaxial cable with many other channels, "baseband" video takes the whole cable, and doesn't even include sound! Baseband video and audio is what comes out of the RCA (a.k.a. "phono") jacks on the back of your VCR. Since it takes two coaxial cables to transport a single baseband video and audio source, you generally want to convert baseband into RF as "early" as possible. Which means as close to the source as possible.
You convert baseband to RF with a device called a modulator. Most modulators today are simple little digital boxes that are similar to, but the reverse of, a cable box. They have inputs for video and audio, and an output for RF. (RF is almost always an "F" type connector.) You can use one or more modulators to create your own "in-house" channels. In effect, you create your own cable TV company.
A cable coming in from your antenna or the cable company contains many RF channels and needs no modulation.
From a "block diagram" standpoint, there are four key pieces to any video distribution system: The coaxial cables themselves, which serve as a conduit for the RF signals and allow interconnecting the other key pieces; RF Amplifiers that "boost" the RF signals to make up for the signal losses the other pieces impose; Combiners which "add" two or more cables together to create a single output that contains all channels from both input cables; And splitters that take a single input cable and distribute the same signal to two or more output cables.
Planning a video distribution system is not difficult. You need to understand what the key pieces do, have a blueprint of your home, and be able to do a little very simple math. That's it!
Ready to Go On?
This application note covers video distribution in four sections:
- The first section describes how to design (and spec out) a system. This section will help you determine what equipment to buy.
- The second section covers prewiring the system. This section will tell you what to do while the walls are still open.
- The third section details the installation of the system components.
- The fourth section describes how to "tune" and troubleshoot your system when you've got everything hooked up.
Please note that this application note is not about home theater systems, although it obviously describes how to get RF signals to and from the home theater system, and how to share home theater video sources with the rest of the home. It does not, however, describe how to interconnect baseband video/audio between the home theater components, or how to carry baseband or s-video signals throughout your home. (A practice we do not recommend.)
Nor does this application note cover whole-house audio distribution. See our Whole-House Audio Tutorial. Although video source components may supply audio to the whole-house audio system, we will treat whole-house audio distribution as a separate system.
This document also does not cover DSS/Satellite signal distribution. See How Do I...Connect Multiple DSS Receivers. To integrate DSS distribution with your video distribution system, design the video distribution system first, then "piggyback" the DSS signals to the appropriate locations on the video distribution cable as described in the DSS document.
Throughout this document you will see highlighted part numbers. These are hyperlinks to more information elsewhere on our website about specific products. Unlike other "sterile" documents that claim to educate you about whole-house audio without actually naming any products or even brands, this document lets you click your way all the way through to actual product specifications, pictures, and prices!
Video Distribution Tutorial - Design
Section 1: Designing a Video Distribution System
This section of the tutorial describes how to design a video distribution system for your needs.
- Dispelling a Few Misconceptions
- Counting INs and OUTs
- Choosing Drop Locations and Calculating Cable Lengths
- Choosing Modulators
- Section 1 Summary
Before beginning, I want to take a moment to dispel a couple of common misconceptions about video distribution. There are two kinds of things you can do when it comes to video distribution: The very easy and not-too-expensive; And the pretty hard and very expensive. In residential video distribution, we have always stayed with the former. Here are some examples from the "pretty hard and very expensive" category:
Combining Coaxial Cables With Common Channels I once said: I'll just combine my in-house UHF channel 22 with the antenna feed. There doesn't seem to be a channel 22 in my area. My channel 22 will surely drown out any little bit of any 22 than is coming in from the antenna. Silly me. It is astounding how little of a signal it takes to screw up a perfectly good signal...when they are on the same frequency. When you "combine" two coaxial cables containing RF signals, you have to be absolutely sure the cables have no frequencies (channels) in common. Combiners are very simple little devices: Essentially they are transformers that simply "sum" the two input signals.
Removing a Channel Let's say that you wanted to remove a channel, or a group of channels from a cable. Either just because you didn't want them in your house, or because you wanted to insert your own channels in their place. The cable companies do this with very precise, and obscenely expensive "notch filters." We don't do it in residential installations at all. The closest we come is with low-pass filters that remove all stations above a certain point. And they are not all that precise: They begin "attenuating" stations at one channel, and as you go up the channels get worse and worse, until you reach the rated cutoff, where the channels are completely gone. This spread can encompass ten or more channels.
Adjacent Channel Modulation Let's say that your local area doesn't have a channel 3 being broadcast. Why can't you just take the RF output of your VCR, which is channel 3, and combine it with your antenna signal so that everyone can watch the VCR? Well, you can...so long as nobody wants to watch channel 2 or channel 4. Modulators (and the channel 3 output from the VCR is coming from a little modulator built-in to the VCR) produce an RF signal that is much "wider" in frequency range than one channel. In order to keep this signal from interfering with the adjacent channels you have to use an extremely precise (and expensive) "narrow-band filter." The cable companies use the filters. In residential applications, we just make sure there is an unused channel above and below any "in-house" inserted channel.
If you keep these three limitations in mind, you won't "design yourself into a corner."
RF Video Distribution Concepts
Integrity of RF SignalsThere are two parts to maintaining the integrity of RF signals; The first part is keeping your signals from leaking out of the cable. The second part is keeping outside signals from leaking into the cable (called "ingress".) When your signals leak out of the cable, it can cause interference on your neighbor's TVs. Besides, it annoys the FCC. If a local broadcast channel leaks into your cable, it will interfere with that channel (though not necessarily the same program) in your distribution system. Both problems are avoided by using good quality RG6 coaxial cable and properly installed high-quality connectors.
Splitters, Combiners, & Taps, Oh My!RF cables are designed to carry RF signals from one point to another, not from one point to many. In other words, you can't run RF signals to multiple locations by wiring all the destinations in parallel. The reason is that the residential RF distribution scheme is based on 75 ohm terminated transmissions. Meaning that the transmitting side expects to see one, and only one, 75 ohm load on the other end of the cable.
A splitter is a small device that has one input (the 75 ohm load) and 2 or more outputs, each driving a separate 75 ohm load. Essentially they are transformers that split the power in the input signal to multiple outputs, while maintaining the 75 ohm impedance. However, there is no free lunch! Every time you split an RF signal with a splitter, you drastically decrease the signal's strength. An RF signal only has so much power. Logic dictates that splitting this signal in two with a "passive" device will result in two signals that each have
A combiner is simply a splitter hooked up backwards. It combines the channels on two or more separate cables onto one cable. The only drawback to this piece of magic, is that the cables being combined cannot have any channels in common with each other. The resulting signal on that channel would be trashed.
Combiners make some neat things possible. Let's say you have cable TV that has channels 2 through 63. And you have a DSS receiver that you would like to be able to see on any TV in the house. You can hook up a modulator to the DSS receiver, set the modulator to channel 65, then combine this new channel back in your wiring closet with the cable TV coming in! Now any TV can watch DSS by simply changing to channel 65. This concept of "in-house" channel generation, together with the new cheaper and more reliable digital modulators, is opening up many new possibilities in residential video distribution.
Taps are similar to splitters, but are "wound crooked" so that the outputs are not equal in signal strength. The "through" output of a tap may only reduce the signal level by a very small amount, while the "tap" output is a small fraction of the signal level. Taps are primarily used in complex commercial distribution installations.
Attenuators are simple "one in, one out" devices that reduce the signal strength. Attenuators come in various sizes and are useful when tuning up the video distribution system.
Calculating RF Signal Loss and Gain
RF signal levels are measured in dBmV which is a logarithmic scale of signal relative to one millivolt. Since decibel values represent power levels, and are logarithmic, they can be calculated with simple addition and subtraction. The main thing to remember about dB (for short) values is that if the level drops below 0 dB (into the negative dB range), you are loosing actual signal information and no amount of amplification will be able to recover this lost information (picture quality.) In fact, amplifying a signal that is below 0 dB will usually make the picture worse since the noise is now being amplified and picked up. So you must insure that your signal levels never drop dangerously near 0 dB anywhere in your distribution system. This is why the main RF amplifier us usually connected near the input side of the distribution system; so the signal is boosted early, and never drops precariously low.
The only way to actually measure the signal level is with an RF signal level meter specifically designed for this task. We ended up buying one (they go for $1000 up) that we rent out to our local customers that are having trouble tuning up their very complex systems. But most folks get by just fine by just doing the calculations up front.
Cable TV companies are supposed to deliver around 15 dB of signal strength at the side of the house, but I've seen this range from below 0 to well over 25 dB. An antenna can deliver a wide range of signal strengths depending on the strength and distance of the stations.
The optimum level at the wall-plate is between 8 and 15 dB.
Counting INs and OUTsBefore you can get to the business of designing the headend, you need to know how many inputs and outputs you need. Cable TV coming in, or the Antenna feed coming in, counts as one (you can't use both simultaneously). Other inputs to the headend will come from modulators generating in-house channels. Modulators are often remotely located (by the equipment they get their A/V signals from) and send their modulated signals to the headend over the "upstream" coaxial cable. Two or more modulators at the same location should be treated as one at the headend since their signals will be combined at the remote location.
Usually, all inputs at the headend are combined separately, then combined with the main cable TV or antenna input. This is so the main input is not attenuated any more than necessary before being amplified. Besides, you have more control over the level of the in-house signals than you do over the cable TV or antenna signals. Also, you can add additional inputs later without greatly affecting the overall video distribution system design.
Outputs are the "downstream" cables that carry the signals to each of the wall plate "drops". It doesn't matter if there is actually a TV connected...the load on the system is the same. (Unused downstream drops should be capped with a terminator.)
If you end up with a lot more drops than you think you will ever have TVs, you can design your headend to handle only a limited number of connections at one time, and switch cables when you move TVs. Most folks, however, design the headend to drive all the drops, whether used or not. Note: Although you should have as many upstream cables coming back to the headend as you have downstream cables, most of the upstream cables will not be connected at any given time. Only the upstream cables that are connected to modulators should be combined into the system.
Now count the number of "in"s that you will have connected to the headend at any one time, and the number of "out"s you want to connect. These numbers will be used later to choose or design the headend.
Choosing Drop Locations and Calculating Cable LengthsNext you need to choose a location for your cable drops. Initially, we just use the cable drop locations noted on the electrical plans. Although these are usually placed by the architect, not the owner, the count
In bedrooms, the cable drop locations are generally opposite the bed location. In the main TV room, the location should be behind the TV/Home Theater. Don't forget to put a drop near the computer in the study! TV on the PC is increasingly easy and popular, as are cable modems. Also run some coax cable and some 4+ conductor telephone wire to the front door location for a security camera. Along with security cameras come the need for a cable drop in the kitchen and other often occupied spaces, so that the owner can easily see through the cameras.
You need to determine a location for the headend. Basements and garages are OK. Although under stairs and closets are a more common location. Attics are out due to excessive heat in the summer. A "central" location is nice, but the vagaries of architecture often don't allow this. Just make sure the location has access, through the walls, to all parts of the house.
One more "drop" will need to run to the cable entrance ("Point Of Demarcation") and/or the antenna location. If yours is new construction and you don't know where your cable will be coming in, check with other homes already built in the area to get a clue. If you have underground service, most often the entrance will be just inside the garage or on an outside wall nearest the street. If you have overhead service, the entrance will be on an outside wall nearest the closest pole. The cable company will run coax and install a grounding block at this point. You will connect to the other side of the grounding block.
Once the approximate locations are determined, you can estimate the cable lengths you'll need. With your ruler, measure the distance from each drop to the headend, always turning at right angles. Multiply by the scale to get the number of feet, then add ten feet to each run to account for ups and downs at each end. Once you've done this for all drops, add the lengths together and add a 20% fudge factor. (Why the fudge factor? Experience. Trust me.) Then multiply by two to account for upstream and downstream runs. Is your number somewhere between 500 and 1000 feet? Most of the time, it is. If less than 500 feet, you must have a home with very few rooms. If over 1000 feet, you're building a pretty impressive place! One 1000 foot spool of coax is the average purchase for our customers.
Designing the HeadendNow that you've figured out how many ins and outs you have, where they go, and how far they go, its time to think about the headend. There's two very different ways to go about this. The first is to choose a preconfigured video distribution panel that is appropriate for your needs. The second is to design your own video headend with what we call "video plumbing." This is where you screw a bunch of components to at piece of plywood on the wall and interconnect them with short pieces of coax. While this is good clean fun, it isn't always the prettiest, or the neatest solution. However, it may meet your needs much better than a preconfigured panel.
Designing the Headend with Discrete Components
For designing a structure wire cabinet see our (How do I wire a structured wire panel?) in our knowledge base
InputsBring in the cable TV or antenna feed into a two input combiner. Then combine the upstream cables together in such a manner that the output of this combination is in the 12 - 19 dB range. (Assume the output of modulators is 25 dB, most are this high or higher, and are adjustable.) Run this signal into the other input of the main combiner. You now have a single cable with balanced blend of CATV/antenna signals and in-house signals in the 8 - 15 dB range.
Minimizing the drop on the main feed is a primary concern since you don't have much control over the strength of this signal. If it happens to be very weak, you don't want it to go below 0 dB in your input stage.
If most of your runs are within one of these categories, you should design a system with all outputs at the same level. An equal-output system is achieved by using a "symmetrical" approach. All splitters at each stage should be the same size. An equal-output design with eight or less outputs needs only a single splitter stage (see Example 1). But for more than eight outputs, you will need two or more splitter stages (Example 4).
Remember that the smaller the splitter, the stronger the output. Thus, use a single large splitter to drive all the short runs, and one or more smaller splitters to drive the longer runs. In an unequal-output system, you will always end up with another level of splitter that drives the final splitters.
AmplificationNow that you have the numbers for the total loss in your system, you can determine how big of a main amplifier you need to counteract these losses.
Main AmplifierAdd up the total loss of your system by adding the loss in the input side to the loss in the output side. For average systems, this number is usually around 25 dB. Choose an amplifier that has at least that much gain. Amplifiers with variable outputs are nice since they let you easily adjust the gain to meet your exact requirements.
The main amplifier will connect your input stage to your output stage. (See Example 2.)
Isolation AmplifierIt is good practice to plan for an isolation amplifier on your main antenna/cable input. This amplifier takes the input antenna/cable signal and amplifies it a little, and the resulting output is then fed into the main antenna/cable input to your distribution system.
The isolation amplifier serves two purposes: It may be needed if the input signal is very low, in order to boost it to a level that is roughly equal to the other inputs so that it can be successfully combined in your input stage. And it keeps your in-house modulated signals from going back up the cable or out of your antenna!
That having been said, in practice I usually find that an isolation amplifier is not needed: The input signal is usually strong enough, and the attenuation between the two inputs of the main combiner is quite high, so your in-house channels shouldn't "leak" back up the cable. There are always, however, exceptions. So at least keep in mind that you may ultimately need an isolation amplifier. (All the pre-configured panels include an isolation amplifier. Apparently the manufacturers believe it is important.)
Designing the Headend with a Distribution PanelThe pre-configured distribution panel approach is much easier and cleaner. Now that your know how many outputs you need, just choose a panel with enough outputs. If the panel you choose doesn't have enough inputs, you can add an external combiner to get all your signals in.
Modulators are devices that take video and audio signals and turn them into an RF channel. Normally, modulators reside near the device that they are creating the channel for, such as a satellite receiver. Although several cables are needed to connect the source to the modulator, a single coaxial cable can carry the audio and video signal to the headend. Exceptions to this include video cameras an other such sources where you might not want the modulator located out by the camera. In these cases, the modulator is usually placed at the headend and the camera's signal is carried in its "baseband" form over coax to the headend.
The exact modulator(s) you choose is up to you. If you have two or more sources at a single location, you can save some money by using a double- or triple-channel modulator.
The NetMedia modulators are smaller and a little less expensive than the Channel Vision line. The Channel Vision modulators are easier to set up, come in more versions, and have a slightly stronger output than the NetMedia line. Our newer product line now includes the CELabs modulators that are small, have channel displays like the Channel Visions. They also have the least expensive one channel stereo modulator.On the high-end Channel Plus offers 3 & 4 channel stereo versions with S-Video inputs. All these modulators are digitally tuned, are drift-free, and perform equally well.
Video Distribution Tutorial - Install
Section 3: Installing a Video Distribution SystemHomeTech Solutions newest update is currently part of our "how to install combo cable" which covers some of the installation for video distribution. Structured Wire Tutorial
Installing Combination Cable
How Do I...Install Combo Cable
This application note describes how to install HomeTech's speed-wrap or combination cable.
This application note only covers installations where the sheet-rock is not yet up. Installing combo cable after the sheet rock is installed is a more complicated process.
What You'll Need
Main Tools Page
Combo Cable Page
What You'll Need
Do's and Don'ts
- Do wait for the electrical and plumbing to be roughed in before installing low-voltage wiring.
- Don't run combo cable within 18" of AC wiring for more than 18".
- Don't run combo cable and AC wiring though the same stud cavity (for more than 18").
- Don't put a mud-ring on the same stud (even the other side) as an electrical box.
- Do cross AC wiring at a right angle.
- Don't kink or step on the combo cable.
- Don't bend the combo cable with a radius of less than 4".
- Don't jerk the cable or pull at an angle to holes. (Doing so could tear the outer jacket and expose the inner cables to damage.
- Do watch for sharp edges that could damage the cable.
- Don't use staples or other securing devices unless you are sure that they will not crush or kink the cable. (Use our cable hangers, cable ties applied loosely with random spacing, or plastic staples larger than the cable.)
- Don't use securing devices inside stud cavities if it can be avoided. (This makes it easier to replace the cable in the unlikely even it is damaged.)
- Do label cables on each end. A marker and masking tapes works fine for temporary use.
- Don't try to splice or repair a cable. Instead, remove it, use the pieces somewhere else, and pull a new cable.
- Don't let the cable lay on the ground in the crawlspace or on the ceiling joists in a main access area in the attic. Instead, support the cable from the roof or floor-joists with J-hooks.
- Do drill through center of stud. This spacing protects the cable from drywall screws. If you must drill closer to one side, use a nail-plate on the face of the stud to protect the cable.
- Do not drill through fire-walls, shear-walls, or specialized members like glue-laminates without first checking with the builder or local codes.
- Do drill holes straight and even when passing cable through several studs at once...the cable will pull much easier.
- Install the headend enclosure per the manufacturer's instructions.
- Place a combo cable spool on your cable reel immediately below the headend enclosure.
- Walk through the structure with your plans and a brightly colored crayon. Mark the studs where the mud-rings will be placed, drawing an arrow to the right or left.
- Install the mud-rings. Use at least two screws, one on each face to hold the plate in place. Measure the height your other electrical boxes, from floor to center, for reference.
- Starting from the headend, feed the cable through the top or bottom of the stud cavity of the headend (no need to pass through the headend knock-outs at this point.) Pull the cable through each hole about 10 feet at a time. Keep working the cable through, 10 feet at a time, until you reach the mud-ring. You'll want about 18" of cable past the mud-ring.
- Bend the center tabs back and secure the cable inside the stud cavity with a tie-wrap. Double-check that the tie-wrap can be cut through the opening, the cable can be fished out, and that there will be at least 18" of slack cable available.
- Pull back any remaining slack towards the headend.
- Cut the cable long enough at the headend so that the end reaches just past the furthest point of the headend box. This will insure that the cable will be able to connect anywhere inside the box.
- Fish the cable through the knockout in the headend can, secure it inside, and label it.
- Repeat for other runs.
An unmodulated video signal. Depending on the regional standard, it may be NTSC, PAL, SECAM, etc. format. NTSC is used throughout North America. This signal does not carry any audio component and "takes up" the entire coaxial cable. Baseband video can be transported over the same kind of cable (I.E. 75 ohm RG-6 dual or quad shield coaxial) as RF video, but never at the same time. Runs of several hundred feet are possible without amplification, but amplification and distribution of baseband video is very different than RF video/audio and is not covered in this document. You can tell a baseband video input or output jack from an RF jack because the baseband jacks are usually non-threaded RCA style connectors.
Short for Cable Access Television. The method for distributing RF signals via coaxial cable rather than radiated through the air.
Short for Multiple Access Television. The method for distributing RF TV signals by broadcasting them through the air.
A method of encoding stereo audio along with the video signal on an RF channel. Many TVs and VCRs can decode this stereo signal. Those that can't simply get the mono audio signal.
One or more video/audio signals modulated to Radio Frequencies. As in TV channels. You can tell an RF input or output jack from a baseband video or line level audio jack because the RF jacks are usually threaded "F" style connectors.
Tuning & Troubleshooting
Section 2: Troubleshooting a Video Distribution System
Please be patient...I'm working as fast as I can...
And, please, no flames about incomplete information. This stuff is free! I'm doing this all on my own time, just because I really love to share information (isn't that what the internet used to be all about?). So I don't take kindly to complaints about unfinished sections.
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