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|TWISTED PAIR WIRING VS. COAX||Published: 11/06/09|
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Most installers and end-users of CCTV equipment use coaxial cable such as RG-59 or RG-6 when transmitting video from a camera back to a DVR. However, there are times when UTP (unshielded twisted pair), or Cat5 type cabling is better and more efficient.
Using UTP requires the addition of powered or unpowered baluns on both ends that basically change the properties of coax transmission over to UTP standards. There are many advantages to changing over to UTP, especially for long distance runs and for cabling between buildings or between floors of a building.
UTP offers improved signal quality over coax, especially for long distances. Other benfits include 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.
When compared to coax, one run of Cat5 UTP wire is smaller in size than RG-59, thus making it much easier to pull and terminate than coax or fiber, as no crimping or termination and/or polishing is involved. Spare pairs of UTP can also be used to deliver RS-485 data to control PTZ's.
UTP delivers a high-quality, flexible, expandable cabling system that uses less conduit space and will fit in with cabling topologies for years to come. For example, when you decide to switch over to network or IP cameras in the future, UTP is the way to go, and you will not need to change the wiring to make the change.
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 punch-down 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. This destroys the inherent noise immunity that UTP is famous for.
- It is safe to install UTP bundles near RF sources, fluorescent lights, motors, generators or high voltage.
- Never place any type of low voltage 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.
- 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.
- 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 most brands of video transceivers, immunity to differences in grounds are built into all active (powered) 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.
- Wiring, joins and terminations are simple and fast when you are building your transmission routes, because it is built much like typical phone closet type layouts such as punch blocks using 66-blocks or 110-blocks to make connections. Most businesses already have these type of punch-down blocks in the IT or wiring closets, so adding a few more for your CCTV installation is easy. Remember, video can be sent through dozens of these type of connections without signal degradation. Newer models of baluns and hubs can also be ordered with RJ-45 type connectors for a cleaner look, and only takes a couple of minutes if you have the correct crimping tool to attach the RJ-45 connectors.
As you can see, installing with UTP is just as easy as running coax. No special skills are required, and it just may solve interference or distance issues on some installations.
by Allen Spears - Chief Engineer Rugged CCTV
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