Selecting the right components is critical to a good quality coax system. Proper termination and installation methods are just as critical.
“Anything you can do, I can do better.”
“I can do anything better than you.”
“No you can’t.”
“Yes I can.”
“No you can’t!”
“Yes I can!” …
An Irving Berlin tune from the musical Annie Get Your Gun? Actually, no. It’s the coaxial-versus-unshielded twisted-pair (UTP) debate heating up in TIA TR-42.
As you may recall from past columns, whenever I spoke of the usefulness of coaxial cabling, a cadre of Ph.D. electrical engineering-types stepped up to the plate to defame that point of view.
This leaves us, as systems designers, installers, and end users, with little recourse except to ferret out the answers on our own, with most of the available “technical support” coming from that same cadre of experts biased toward supporting all services on UTP.
The category of UTP recommended usually depends on what product they are selling. If they are selling cabling, then of course you need the latest Augmented Category 6. But if they are selling equipment, then Category 5 or 5e will be just fine.
When in doubt, form a committee
With only logic, common sense, and 30-plus years’ experience in the cabling industry to my credit, I know when I am outgunned. So, I called on coaxial-cabling manufacturing and system-design engineers to help balance this discussion. Thanks in part to John Pryma of Honeywell Genesis Series Cable, this more or less snowballed into a Coaxial Cabling Study Group under TIA Technical Committee TR-42.
And after several meetings and teleconferences, the group has a message for us in the form of a letter.
Dear Residential Coaxial Cabling Installer/User:
The Telecommunications Industry Association (TIA) Technical Committee TR-42 User Premises Telecommunications Cabling Infrastructure develops and maintains telecommunications standards for copper cabling including coaxial cable (coax) for residential applications. Quality coax provides a wide bandwidth, minimal signal loss, low signal leakage and low distortion. Inferior cabling, which may include coax cable, connectors, installation and termination practices, may result in poor picture quality with ‘snowy’ ghosting, lines, and spot noise. In extreme cases, no picture may be displayed. Emerging applications such as high-definition television (HDTV) and broadband Internet access require good quality coax cabling.
Poor quality cabling can also lead to radio frequency (RF) signal leakage, which may interfere with other communications systems, such as aviation or emergency services. Multiple service providers (MSOs) are responsible legally and financially for leakage from their entire system, including customer-owned cabling. The local service provider may refuse to connect service if the cabling is of inferior quality.
One way to avoid poor quality coax is to evaluate the design. The center conductor should be copper-covered steel. The insulation or dielectric over the center conductor must be foamed plastic, typically white in color. Avoid cables with solid plastic dielectric. The insulation must be covered with a metallic foil and braid shield. Avoid coax cables without the foil. The braid coverage should be more than 60% of the surface area of the foil. The outer sheath or jacket must fully enclose the shielded core and be free of voids or skips. The jacket must be marked with the appropriate rating(s) for your local building codes and standards.
The connector you specify must fit the coax you have selected. Multiple coax and connectors are available. Consult your MSO, distributor, or supplier for specific recommendations. Modern compression-style connectors provide enhanced electrical and mechanical performance when compared to crimp-on style connectors.
Selecting the right components is critical to a good quality coax system. Proper termination and installation methods are just as critical as the components themselves. A special cable-preparation tool design for the cable and connector you are using is recommended. The tool will help prepare the coax for the connector. The center conductor should be exposed for 3/8-inch and free from any plastic from the insulation or dirt/contamination. The aluminum foil tape should still be fully glued to the white dielectric. The braid wire should be folded back over the outer jacket, not touching the center conductor. Any loose pieces of plastic or metal must be removed.
The layout of the coax should be homerun style. Each coax should be routed back to a single location, which will house all active (amplifiers) and passive (splitters) devices associated with the installation. This may be close to the cable service entrance or centrally located within the residences (see ANSI/TIA/EIA-570-B). Avoid ‘daisy chaining’ cables and outlets with splitters, especially behind walls where they are not accessible. Cables should be routed around corners without violating the minimum bend radius. No 90-degree bends! The coax should be secured using products (staples designed for the cable or plastic cable ties) that do not deform the cable jacket.
After the cable is installed, the system should be tested. Commercially available testers provide detailed information on the performance of the system. Alternately, a simple functional test with a television set can show quality issues as mentioned previously. Documentation of the installed performance may help avoid future issues with the coax system.
There is a wealth of information available from your MSO, distributor, and suppliers. Additionally, there are standards, such as ANSI/TIA/EIA-570-B Residential Telecommunications Infrastructure Standard. Other applicable standards are available from the Society of Cable Television Engineers (SCTE) and the Satellite Broadcasting and Communications Association (SBCA).
Respectfully,
TIA TR-42
But is one letter enough? Hardly.
Most “how to achieve success” classes can be boiled down to one sentence: “If you want to be successful at something, do what successful people do.”
Let’s get together
On June 20, 2002, TIA published ANSI/TIA/EIA-568-B.2-1, which added Category 6 to the TIA-568 standard. So, what do you do when you think you have a better mousetrap and want to get the consumers’ attention? Get a group of manufacturers, distributors, and user groups together and form a consortium. A consortium is an association of companies with the objective of participating in a common activity or pooling their resources for achieving a common goal.
In this case a consortium was formed to promote the adoption of Category 6. To begin this initiative, the Category 6 Consortium released frequently asked questions (FAQs) and provided consumers with an update on Category 6 cabling and applications standards, as well as additional references for finding Category 6 information and products.
And very soon, a Coaxial Cabling Consortium will be formed to promote the use of coaxial cable. But until then, here are a few points to ponder:
Q: Why use a copper-covered steel-center conductor?
A: Tensile strength. Steel is stronger than copper.
Q: Why require a bonded foil?
A: To reduce electromagnetic interference (EMI)/radio-frequency interference (RFI).
Q: Why use a minimum 60% aluminum braid?
A: To enhance mechanical properties and provide greater shield effectiveness.
Q: Why require a minimum 5-MHz to 1-GHz sweep test?
A: To ensure performance across a greater bandwidth to meet the needs of today’s more-demanding architectures and in preparation for what is next. Serial digital coaxial cables are tested to 3 GHz.
Q: Why require a minimum 23-dB signal return loss (SRL)?
A: To improve signal quality and reduce signal reflections.
Q: Why require that the cable dimensions conform to SCTE specifications?
A: To ensure a suitable cable-to-connector/fitting interface, and reduce signal leakage.
Q: Why is it so important that the coaxial drop cable remain round?
A: To ensure shielding integrity and signal quality. It is also important to keep the minimum-bending radius 10 times the outside diameter of the cable and to avoid kinking, crushing, or flattening the cable. When unreeling the cable, use a cable-reel caddy. This will allow the cable to roll off the reel evenly and prevent it from forming loops or fish-eyes. Damage to the cable jacket or shielding caused by pulling the cable against itself, or over rough or sharp edges, or bending the cable too sharply will deteriorate the overall electrical performance. This cannot be repaired with electrical tape or re-rounding of the cable. You must replace the cable.
DONNA BALLAST is BICSI’s standards representative, and a BICSI registered communications distribution designer (RCDD). Send your questions to Donna via e-mail: [email protected]