By using unshielded twisted pair transmission, CCTV system designers can offer their customers more bang for their buck.
By Guy Apple
Installing unshielded twisted pair transmission systems affords CCTV installers and designers the opportunity to provide customers with a clean-looking rack room, as well as a cabling system that uses less conduit space.
Every installer knows that CCTV transmission systems can be the weakest link in delivering the high quality video that customers expect and deserve. That is why more and more installers are turning to CCTV transmission systems based on unshielded twisted pair (UTP).
Not only is UTP the way of the future, but it is also the first choice for many of today's well-planned installations. UTP offers improved signal quality over coax, plus features such as ground-lifting, substantially improved interference immunity and built-in transient protection - all necessary elements to consider in today's world of sensitive digital video recorders. And, because UTP transmission systems can be designed in the same fashion as telephone and data networks, installation costs can be substantially reduced.
When compared to coax, one pair of UTP wire is about 1/10 the size of RG-59. UTP costs as little as 1/10 that of non-plenum RG-59 and only 1/20 that of plenum-rated coax. UTP's small physical size makes it much easier to pull and terminate than coax or fibre, as no crimping or termination and/or polishing is involved. Spare pairs of UTP can also be used to deliver RS-422 data or short distance, low-voltage power to the camera.
When compared to fibre, UTP transmission systems are less costly, from cable and installation cost perspectives, and from tooling and transceivers, and still offer similar quality. Although, for extremely long runs (i.e., more than 8,000 feet), or if the video run must reside in the same conduit at high-voltage power, fibre is still the way to go.
These benefits have prompted many camera manufacturers - for example, Aigis, Bosch, CBC, Extreme CCTV, GE Security, Honeywell, JVC, Pelco, Sony, Vicon and Videolarm - to embrace the technology by offering a built-in UTP output. It has also prompted thousands of large and small projects to standardize their video needs with UTP because it delivers a high-quality, flexible, expandable cabling system that uses less conduit space and will fit in with cabling topologies for years to come.
As for installation, here are some tips to consider the next time a UTP transmission system is desired:
. It is best to use point-to-point UTP wire, Category 2 or better, and 24 gauge or thicker. Wire may be stranded or solid; the latter is compatible with insulation-displacement termination systems, such as punch-blocks.
. Never use shielded twisted-pair wire, although multi-pair cables (six or more pairs) with an overall shield are acceptable.
. Do not use un-twisted wire or "quad-wire".
. It is safe to install UTP bundles near RF sources, fluorescent lights, motors, generators or high voltage.
. Always follow national electrical code and provincial, local or other safety requirements.
. Never place signals in the same conduit with high-voltage power.
. A video signal may co-exist in the same wire bundle as other video, telephone, data, control signals or low-voltage power.
. Because a 25-pair cable has only one plenum jacket, a single pair of UTP can cost as little as five percent of plenum-rated coax. All of the homeruns from wiring closets are significantly less costly than pulling the equivalent coax.
. When designing a phone or data system, plan for expansion by pulling more cable than is initially needed. This will save time in the future. A 25-pair bundle is about the same size and cost as three coax cables. Over 10 times the UTP cable can be pulled in the same conduit space as coax. This is especially important in locations where low-voltage cable must be in conduit. Running video and low-voltage camera power in the same bundle saves additional time and money.
. Specified distance includes any coax in the path. Wire resistance may be measured with an ohm-meter by shorting the two conductors together at the far end and measuring the loop-resistance out and back.
. Video signals traveling in opposite directions may co-exist in the same wire bundle up to 1,000 feet, or 2,000 feet if Category 5 or better wire is used.
. Most video transceivers require no power. Single amplified units typically need 12 to 24VAC or DC, while multi-channel active receiver hubs generally have their power supply built-in.
. In leading brands of video transceivers, immunity to differences in grounds are built into all active models. This eliminates annoying ground loops that may be found when connecting from building to building or floor to floor. Ground immunity is preserved when an active receiver is used with any passive model.
. CCTV systems should be designed similar to phone/data systems: punch down the UTP wire using 66-blocks or 110-blocks to make connections. Remember, video can be sent through dozens of these connections without signal degradation.
. To improve rack-space efficiency, several UTP CCTV manufacturers offer high-density, multi-channel hub solutions in which as many as 32 camera signals can be received in one rack space.
UTP transmission technology is always evolving with one new development being a built-in distribution amplifier, which eliminates the need to buy a more expensive matrix with multiple loop through and/or a separate distribution amplifier. Another new development is in the area of connectivity, in which several UTP CCTV suppliers are now featuring different connector options, such as RJ-45 inputs on multi-channel receiver hubs.
As one can see, installing a UTP transmission system is actually quite simple, especially when compared to installing coaxial cable. No special skills are required, and most importantly it often helps dealers and installers provide their customers more bang for the buck.
Guy Apple is the vice-president of Network Video Technologies, a California-based developer of video transceivers and hub systems for the transport of full-motion, colour video and audio over ordinary, unshielded telephone wire.