Getting Video From Point A to Point B
As the various technologies and associated equipment change the landscape of the video surveillance industry, a byproduct of this change seems to get little attention: signal transmission. Regardless of the technologies used, it is still necessary to get a video signal from one point to another, whether that signal be analog or digital, composite or IP based.
Since I often encounter confusion between signal type and cable type, and a bias as to the method a particular systems integrator is used to, I thought this would be a good time to revisit signal transmission methods. We’ll take a look at their strengths and weaknesses, and offer a real-world opinion as to the direction the market is going.
Coaxial Cable: The Beginning
First, let’s dispel some myths about coaxial cable. There is nothing inherently wrong with coax, the medium of choice for roughly 40 years. There is still more of it installed than all other video transmission methods combined, and many folks use it today and plan on using it forever.
When properly installed, coax can carry a relatively high bandwidth signal great distances with very predictable signal loss that can be offset by several types of signal equalization. It is cheap, easy to work with and available everywhere. So why does everyone believe it is going away, and why do I advise my clients to steer clear of it?
The main problem with coax is that there are so many types available that you really need to know what you are doing to specify and install it, yet few people consistently get it right. A key to understanding this is the phrase “when properly installed.”
The fact is that coax is improperly installed more often than not, and the end result is a degraded, unreliable video signal, full of noise and lacking sharpness and detail. The most common reason for poor signal quality over coaxial is the selection of the cable itself.
There are numerous types of cable, all beginning with the letters “RG.” RG stands for radio guide, and the number that follows is the page in the military specification for coaxial cable starting in the 1930s. So a lower number (such as RG6) was developed earlier than a higher number (RG59). Other than relative age, the number does not correspond to anything that relates to the video signal.
The various coax types have different diameters and mechanical composition that affect the cable’s distance limitations and suitability for signal. In general, the thicker the center wire, the longer the cable can be run. However, there are different impedances available (50-ohm or 75-ohm), and different materials used depending on whether the cable will be carrying composite (base-band) video (common in the video surveillance industry), broadband video (cable-TV) or data (such as cable modems).
Each classification allows for a number of variations; a RG59 cable can have a 20AWG solid copper center conductor and braided copper shield, while another may have a 22AWG copper-clad steel center conductor with a foil shield. Both are called RG59, and the first type will work well for CCTV applications while the second will not. Similar variations are common for all types of coaxial cables.
Connectors are another issue.
UTP: The Emerging Standard
Unshielded twisted-pair (UTP) cable is also available in a variety of configurations, called categories, and abbreviated CAT. Unlike coaxial cable, however, it is backwards compatible, so a higher number, such as CAT-5 will provide equal or better performance to a lower numbered cable like CAT-3. For this reason, most installers refer to UTP as CAT-5 cable, even when referring to higher grades such as CAT-5e or CAT-6.
For most digital or analog video applications, CAT-5e cable is more than sufficient. In its most common format it includes four twisted pairs of wire in a single jacket. Lower grade cables such as CAT-3 are designed for telecommunications and will work for analog video, while higher grade cable (CAT-6) performs as well as CAT-5e but costs more, is harder to work with and doesn’t provide better performance except in specialized applications (such as interconnecting digital video servers and encoders in a rack room).
UTP is also an excellent choice for ensuring a facility can accept a variety of signal types. The same cable can be used to transmit IP-based video signals, analog cameras, or even a combination of both (since IP signals do not use all four pairs of wire in a CAT-5 cable, spare pairs can be used to support legacy analog cameras). It can support data for PTZ functions, can provide power for cameras (when the proper Class-2 power supplies are used), and can even be purchased in higher pair counts for structured wiring applications.
Fiber: The Great Problem SolverFiber-optic cable is preferred in applications where signals must be run across great distances. UTP has limitations when used for IP video, while fiber’s limitations are essentially theoretical; with the proper equipment you can go as far as you’d like.
Since a fiber-optic cable is nonconductive, it is also an excellent transmission method when running a signal to various buildings with different electrical grounds, or for outdoor cameras where there’s a risk of lightning. As a backbone, fiber-optic cable provides greater bandwidth than UTP and multistrand fiber-optic cables can carry huge numbers of video, data and other signals with room for future growth.
The drawbacks to fiber are few but significant. Like coax, a properly trained technician can reliably terminate fiber with ease, but an unskilled one can botch the job in numerous and creative ways.
What About Wireless?
There are a variety of niche technologies available, which work well but have not made it to the mainstream. This is primarily due to their expense relative to more established technologies, and wireless is one of them.
In general, it is a bad idea to plan a facility based on a wireless topology. Cable of any type costs less than wireless, the signals from a hardwired system are more reliable, less prone to interruptions and more immune to sabotage or other outside factors. Since cameras invariably require power, you need to get a wire to them anyway, so why not run a signal wire at the same time?
However, wireless technologies are catching on in unexpected areas, enhancing the versatility of systems by allowing applications that were previously unavailable. For example, if outdoor cameras are added on light poles after a facility is built, wireless may be a more cost-effective alternative than saw-cutting the parking lot, and less unsightly than aerial wires. Wireless is also a great transmission method for cameras across the street looking at your building, without requiring right-of-way permission.
Proper Cable Keeps Future Open While the selection of a signal transmission method may seem dull in comparison to the other more complex technical decisions on your plate, it is critical to your customer. We’re at a crossroads in technology right now with analog still the dominant medium (despite hype to the contrary) and IP-based systems steadily increasing in popularity.
At any technology transition point, infrastructure becomes more critical. The cabling infrastructure should outlast the installed equipment, and when the time comes to replace the equipment, it will be less costly if some consideration was given to future proofing the system at inception.
For the c
omplete version of t his story, see the August issue of Security Sales & Integrat
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