Published In December 2000
Electronic technology is among the fastest changing industries in the world. As technology changes, more sophisticated equipment is developed. With new technology and equipment come changes in the method of connecting the equipment in both new and existing buildings. The term “backwards compatibility” must be understood before any questions can be asked or answered. The difficulty of explaining the term is really predicated upon the scope of the technology to be covered and the age of the electronic equipment. Even 10 years’ worth of material is an extremely large amount to cover, since many different cables and connectors have been developed over this decade. Backwards compatibility is the ability to connect old technology cables and equipment to new technology equipment without replacing all the components within the system. Is the old cable compatible with new equipment jacks, or is an adapter available to provide conversion to match the new jacks? Can the old cable even be used, since new equipment being installed may use extremely high frequency and require Category 5 or higher-grade cable to operate at maximum efficiency? Will the new system function adequately with an existing cable or must a lower impedance cable be installed and, if a new cable is required, how extensive will the recabling project be? These questions and more must be answered early in the system design stage so money can be realistically budgeted to cover new system installation costs. New equipment must be studied and compared to old equipment with a list of upgrades necessary for connection. Will the existing cable provide the necessary low impedance and good signal-to-noise ratio with little “cross-talk” between conductors? The higher the frequency being used, the more critical are the positioning of the conductors, the number of twists per foot in the cable, and the conductivity of the connection point. Many new conductor connectors use an excellent grade of gold-plated contacts for better conductivity and lower impedance. Less costly connectors can be purchased, usually made of copper or tin with nickel or chromium plating. One of the first systems to be upgraded or made “compatible” is the basic telecommunications or telephone system. Most telephone systems in office buildings and residential homes have been upgraded from the old rotary mechanical telephones to new electronic ones. Where a 25-pair telephone cable was required in the past for a multiline, multifunction telephone, this can now be accomplished using a two pair cable. The old hard-wired jack can be converted into the new modular plug-in style by installing a wall jack adapter. Using the accompanying picture and referencing the various adapters within a clock setting, the adapter at the 11:00 position is a single- to triple-modular telephone adapter. The 12:00 position adapter is a hard wire to modular adapter, and the 1:00 position is the modular telephone cable, available in any length from 12 inches to 25 feet or more. These devices can permit much of the existing telephone cable to be used along with its existing support structure, such as telephone punch-down blocks and cross-connect arrays, without major changes to the system. A good system inventory should be done to determine the location of each cable and jack with proper labeling at the jack and at the cross-connect array. Since many offices, as well as homes, are using cable access television (CATV) or closed-circuit TV (CCTV) systems in their educational training rooms, media rooms, or conference rooms, a detailed look at the connection devices for this technology is a must. The basic cable used to connect the satellite or TV antenna to the receiver or from the cable connection at the network interface unit (assuming an outside signal is being used) to the receiver is a coaxial cable. To increase system flexibility and reduce the amount of cable used, the coaxial cable can be split into two separate cables using a splitter (at the 7:00 position) or an indoor or outdoor diplexer (at the 10:00 position). Or, it can be combined to allow multiple signals on a single cable (the two signal combiners/splitters are shown at the 9:00 position). This allows a more diverse use of a single cable from two separate sources of signal. A coaxial cable splitter splits one coaxial cable into two coaxial cable leads that can be routed to different locations. An example of a system using a splitter would be a regular cable TV system with multiple TV locations. A diplexer permits the coaxial cable to be split into two different cables but with a voltage passed through the diplexer to each cable. An example of a diplexer being used is a satellite dish system where an antenna is connected to a satellite receiver and the coaxial cable between the antenna and the receiver carries a voltage. A combiner/splitter permits the coaxial TV cable from the interface unit on the building and the coaxial cable from the satellite antenna to be combined on one coaxial cable feeding to the video unit. A splitter is not interchangeable with a diplexer, since a splitter is not designed to pass voltages from one side to the other of the unit. This is a very complex and ever-changing market, of which this article just barely scratches the surface. ODE is a staff engineering associate at Underwriters Laboratories, Inc., in Research Triangle Park, N.C. He can be reached at (919) 549-1726 or by e-mail at firstname.lastname@example.org.