Selecting the right cable for an A/V application, from the many different types available, can be a daunting task. Fortunately, although cable varies greatly in size, performance, quality, and capability, most of the cables used in the A/V industry fall within five main groups: individual conductor, twisted-pair, coaxial, fiber optic, and custom bundles. In this section, we'll look at the cables most commonly used in our industry.
Coaxial
Coaxial cable consists of two separate conductors that are organized into a more complex electrical arrangement. The center conductor carries the signal, while the outer conductor, or shield, provides an internal return path for the signal current. The shield also protects the center conductor and, therefore, the primary signal, from outside electrical interference. The two conductors are separated by an insulating material called the "dielectric". The dielectric, along with the ratio of the center conductor diameter to the shield inside diameter, establishes the electrical characteristics of the cable. The dielectric also provides physical protection for the center conductor. All of these components are jacketed to make one cable.
The impedance of standard coaxial cable, as used in the A/V industry, is 75 ohms. Coaxial cable is the workhorse of our industry and supports all types of video and audio transmission including RF distribution, video distribution, and digital audio, amongst others. The more complex design of coaxial cable often results in it being more expensive than twisted-pair cable; however, coax provides excellent performance, good shielding characteristics, and very reliable operating life. Coaxial cable is manufactured in a wide variety of sizes that will support extensive run lengths; the smaller wire size in Twisted Pair cabling, on the other hand, can significantly limit its application.
When selecting coaxial cable, it is important to consider these factors:
- The highest frequency and resolution of the source signal
- Cable run distance
- Loss per unit length of available coaxial cables
- Cable flexibility and handling environment
- Type of connectors desired and their ruggedness for the application
Twisted Pair
Twisted-pair cable has become ubiquitous due to its use in computer networks. The cable is available in two styles: unshielded twisted-pair, or UTP, and shielded twisted-pair, or STP. Both styles may be found in many types of environments, from telephony to video to professional audio. Twisted-pair cable consists of one or more groups of two individual conductors, twisted together at a regular interval to form one pair. While common UTP and STP conductor sizes range from about 20 to 24 gauge, impedance ranges over 100 to 150 ohms. Twisted-pair cable is characterized as relatively inexpensive and easy to work with. By design, twisted-pair conductors are highly immune to outside electromagnetic interference when implemented as a differential signal transmission method, even though the conductors themselves are not shielded. The following summarizes key attributes of UTP and STP cable:
- UTP cable — UTP is commonly used in telecommunications and computer networking environments. UTP is utilized for low cost transmission of the various data transfer rates demanded by computer networks. For example, popular Category 5/5e cable accommodates transmission rates to 100 megabits per second, while Category 6 cable supports data rates of several hundred megabits per second.
- STP cable — STP cable construction is similar to that of UTP, with the addition of an enclosing braid shield or a foil shield with drain wire around each pair. The shield provides additional isolation of the cable pair from radio frequency interference and electromagnetic interference and, in addition, significantly reduces crosstalk within the cable bundle as well. This is of great importance for data transmission rates operating above 100 megabits per second. The drain wire or the braid must be properly connected to the signal ground connections within the data connectors in order for the shielding to be effective.
Fiber Optic
Fiber optic cable is a great choice for hard-wired signal transmission over long distances ranging into the miles or kilometers. This is due to its extremely low attenuation characteristics, or low signal loss, of the glass fiber. Fiber optic cable transmits light photons instead of the electrons transmitted along copper or other metallic conductors.
Fiber optic signal transmission is immune to many of the effects that reduce signal quality in traditional wired environments and therefore offers many advantages over wire, such as complete immunity from outside interference, small size or diameter, light weight, low attenuation, and higher security. Although fiber optics may appear to be the ultimate signal transmission method, there are some drawbacks, such as higher system cost, the complexity of cable termination, and system performance limitations, depending on your total A/V system requirements.
Custom Bundles
Cabling may be customized into bundles carrying the same type or a variety of types of conductors. This catalog highlights several cable bundles designed to simplify A/V system installations by providing a mixture of conductors tailored to support typical application requirements, such as dedicated VGA connections.
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General Purpose Cable — General purpose cables carry a fire safety rating of CL2, CL3, or CM depending on the type of cable and the service provided. Cables in this classification are commonly used for exposed patch cables, cabling within metallic conduit, and cabling within enclosed structures that are not air handling plenums.
Plenum Cable — Local fire codes dictate the cable safety requirements for your specific area. Typically, cables used in plenum air spaces must be run through electrical conduit or be plenum-rated, such as CL2P, CL3P, or CMP. Plenum-rated cables utilize special halogen compounds in the insulation material that are designed to produce very low flame and smoke output in the event the cable is exposed to fire. Plenum cable, while higher in cost, can potentially eliminate the need for metallic conduit in open air spaces, thus reducing overall installation costs.
Halogen-Free Cable — European safety code requirements dictate use of halogen-free cable in most all construction. Halogen-free cables are characterized by use of a zero halogen jacket material having low smoke and fume performance that meets the IEC 33203 flame test, IEC 61034 smoke test, and IEC 754-1 corrosivity test.
The materials from which the cable jacket is made can significantly impact the cable's physical flexibility. While current plenum and non-halogen cable constructions exhibit improved flexibility, expect that these cable styles will be more rigid and somewhat more difficult to handle during installation than comparable non-plenum style cables.
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When purchasing cable, there are three factors that should be addressed before a decision is made. This will increase the chances that the right cable is being used for the job.
- Versatility — Consider the application for which the cable is to be used. Is it a temporary or permanent installation? Are there specific fire code requirements impacting installation time, cost, or methods? What is the likelihood that the system will need expansion or upgrade in the foreseeable future? Consider installing cable types that contribute to the ease of system upgrade and expansion.
- Performance — Consider the type and performance level of sources to be distributed throughout the system design. This is a key consideration, as signal performance diminishes rapidly with long cable runs. Since there are many signal types and frequencies associated with A/V equipment, cable performance is paramount when considering expansion and upgrade as mentioned above. In applications where sources or displays are likely to be replaced in the future, a high-performance, reliable cable infrastructure is not only a good idea, but insurance against incurring significant costs in the future.
- Price — While the total cost of the cable infrastructure can significantly impact the overall cost of a system, there is no significant difference in labor cost between the installation of higher performance cable and that of low cost, limited performance cable. The incremental cost of better quality cabling is often less expensive than the appliances connected to it. Yet, the amount and quality of cable included within the system design is often the last component addressed in the design stage. Cutting corners on cabling, to meet budgetary constraints, will never improve final image quality. The old adage, "You get what you pay for", definitely holds true for cable infrastructures.
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Extron offers the following categories of cables and components to meet the needs of every application environment:
Bulk Cables
Bulk Cables are sold in spools of 250 feet (75 m), 500 feet (150 m), and 1,000 feet (300 m).
Cables & Adapters
Pre-terminated cables are sold in a variety of lengths ranging from three feet to 100 feet and are available with a variety of connectors. They are also available as install kits with one end unterminated so that cable runs are easier to pull and maneuver. Adapters are available for a variety of audio, video, and control applications. These products are indispensable for solving differing mechanical connectivity conflicts. Adapters typically feature a different type of connector on each end. For more information, see the Cables & Adapters section in this catalog.
Custom Cables
Custom Cables is a specialized service offering made-to-order solutions for most cable connection applications.
Crimp Connectors and Accessories
Crimp Connectors and Accessories include Universal Termination Kits, the Extron Universal Crimp Tool, the Hand Wire Stripper, a wide variety of high quality crimp connectors and strain reliefs that simplify the in-field termination process and ensure quick and reliable connections.
Compression Connectors and Accessories
Compression Connectors and Accessories include BNC Compression Kits, the Universal Compression Tool, the Compression Coax Prep Tool, and a wide variety of high quality nickel and gold-plated connectors that simplify the in-field termination process and ensure professional and reliable connections.
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