Cable Choice Can Make or Break a CCTV System
One of the most difficult, yet diverse, technologies security contractors work with on a daily basis is CCTV. One of the factors that make video surveillance systems so challenging is the high demand it places on so little signal.
The video signal security uses is a mere 1.4V (peak to peak). This means it is highly susceptible to sources of radio frequency interference (RFI) and electromagnetic interference (EMI). Not only that, but a camera’s video signal can vary between 30Hz and 6MHz, which is quite a range of frequencies for any analog transmission media.
There are three basic cable technologies security dealers and systems integrators use when installing professional-grade CCTV systems: coaxial cable, unshielded twisted pair (UTP) and fiber optics.
Coaxial cable has a successful history in the security industry and has served well. UTP cable also is a valid selection, but knowing when to use it is important. Fiber-optic cable is also viable in certain situations, but it is not used as much as coaxial and UTP for inside applications.
Armed with this general knowledge, we can proceed forward and delve more deeply into when, how and why to deploy the different types of CCTV system cabling.
Coax Is a Popular Choice That Serves Basic Installations Well
Most of the time, security dealers like to use coax cable to carry their video signals from camera to monitor. This is because it is easy to use and relatively inexpensive.
There are many types of coaxial cable, the most common being 75-Ohm unbalanced and 124-Ohm balanced twin-axial. The former is the most commonly used by most security contactors.
Unbalanced coax typically consists of an outer jacket, an inner braid and a dielectric around a center core conductor (see diagram on page 57 of February issue). The braid acts as ground and constitutes the return path for the video signal. The center conductor carries the hot side of the video and is contained inside the dielectric, which is surrounded and protected by the braid.
At its most basic, a CCTV system consists of a lone camera and a simple video monitor. Of course, most video systems are more complicated than that. For example, some systems require the use of pan/tilt/zoom (p/t/z) devices.
In this case, coaxial will work just as well as any other cable type, especially when using up-the-coax p/t/z control. Where camera control is not to be performed over the coax, a separate twisted-pair cable — usually 18 AWG (American wire gauge, which indicates the diameter) — can be used.
No matter which cabling is used for the main camera runs, coax is usually responsible for bringing together the various devices found at the head-end.
Achieving Optimal Operating Distance Using Common Coax
All security devices today have a 75-Ohm output. In order to maintain video quality, the camera’s 75-Ohm output must be matched with the monitor’s 75-Ohm input. This means 75-Ohm coax is needed. Additionally, the correct cable specification includes a code, such as RG59/U.
When choosing coax, security contractors need to be mindful of several factors, including distance, environment and any sources of EMI and RFI that could cause problems with the video signal.
In terms of distance, the following RF/U cable list may be used when selecting a coaxial cable for a particular job.
- RG59/U @ up to 750 feet
- RG6/U @ up to 1,500 feet
- RG11/U @ 1,800 feet or more
Some sources of cable information hold that RF59/U is good for up to 1,000 feet. Although a usable signal may be possible at this distance, quality may suffer in the trade.
“Distances up to 750 feet over RG59/U can be attained, but as the distance begins to exceed this limitation the color burst begins to diminish and the frequency begins to become distorted due to attenuation in the cables,” says Chad Szekeres, national sales manager with Nitek of Rolling Meadows, Ill.
One solution, Szekeres says, is to install inline amplifiers, which will help preserve the quality of a video signal for greater distances. For example, with RG59/U, using an amp will boost the effective operating distance from 750 feet to 3,400 feet. With RG6/U, you can go up to 4,800. With RG11/U, distances of up to 6,500 feet can be achieved.
Unshielded Twisted-Pair Cable Greatly Expands Video Capabilities
UTP consists of an outer jacket and a number of twisted conductors that form pairs of wires. The most common UTP type is telecommunication cable, often referred to as Category 5, 5e or 6.
“Sometimes called Category cable, UTP cable is generally 22- or 24-gauge copper wire that is twisted into pairs, with each pair color-coded for easy tracing,” says Guy Apple, vice president of marketing with Network Video Technology (NVT) of Redwood, Calif. “Bundles can range from two to 2,400 pairs and are available in plenum, PVC, direct burial, gopher resistant, aerial and more.”
Like its coaxial counterpart, UTP provides real-time viewing of video between camera and monitor. However, that’s where the similarities end.
“Unlike coax, UTP is a balanced line system that consists of an impedance of 100 Ohms,” adds Szekeres. “The 100-Ohm impedance UTP cable is impervious to noise. The outermost insulation creates a housing to protect the multipair cable. Each of the copper pairs is color-coded, making it possible to splice and terminate quickly and easily without changing polarity.”
UTP is exceptionally good at rejecting stray EMI and RFI because of the way it is constructed. “With UTP, video signals can also reside in the same wire bundle with ringing telephones, Ethernet, 24VAC, RS-422, RS-485 and other video signals,” says Apple.
Another factor that makes UTP a good choice compared to coax is the relative size difference. For example, Cat-5e cable can carry up to four video signals in a single cable compared to one in coax.
3 UTP CCTV Arrangements Installers Can Put to Good Use
There are three basic flavors of UTP in use today. In their pure form, they are passive and active, with a third that employs a combination of the other two.
A passive system does not require external power, other than the video signal itself. In an active system, an external source of power is used to operate the transceiver units. A third type, according to NVT’s Apple, involves a hybrid mix where a passive transceiver is used to transmit to an active unit.
“Totally passive systems are for short distances. They are low in cost and support ‘up-the-coax’ p/t/z control. The signal loss through the wire is similar to RG59/U, so UTP can be used for normal resolution cameras and analog recording/multiplexing up to 1,000 feet,” Apple says.
Distances attainable using the different types of UTP:
Passive to passive = 1,000 feet
Passive to active = 3,000 feet
Active to active = 8,000 feet
Some camera manufacturers now include a UTP transmitter inside their cameras. If a security contractor uses such cameras, it can provide a price advantage.
One of the drawbacks associated with active UTP systems, according to Apple, is that these transceivers do not usually support up-the-coax camera control.
Fiber Optics Handle Long-Haul Applications, Interference Issues
There are times when security dealers find it necessary to send a video signal for several thousand feet, or even miles. As mentioned, UTP can handle distances of up to 8,000 feet when using an active-to-active setup. Another alternative, however, is fiber-optic cable.
“For runs longer than 5,000 feet, single-mode fiber may be recommended, and the use of plastic fiber is typically discouraged. Using fiber-optic cable eliminates the problems encountered with coaxials at distances over 1,000 feet, which is the l
imitation of standard RG59/U,” says Frank Luft, networking systems specialist with Graybar of St. Louis.
One way to visualize how fiber-optic cable functions is to view it like the wave guide used in a microwave-based system. It is made up of an outer jacket; strength members for pulling; a buffer jacket; silicone coating; silica cladding; and a silica core, which is the glass fiber strand at the center of the cable. Where coaxial is good for a frequency range of 30Hz to 10MHz, fiber-optic cable is good up to 100MHz.
What Single-Mode and Multimode Fiber Can Do for You
There are two types of fiber-optic cable used for security purposes. One is referred to as single mode, the other as multimode. In a single-mode fiber-optic cable, the diameter of the core is 5ìm to 10ìm (micrometers), compared to a multimode fiber-optic cable, which is 50ìm to 1,000ìm.
Single-mode fiber-optic cable is essentially smaller in diameter than multimode, and it is designed to accommodate only one primary mode. It is also generally less expensive than multimode cable and is used for long-haul applications, such as telephone service.
Multimode fiber is designed to handle more than one light mode at the same time. Like the prism effect, some modes will disperse at different angles in the multimode cable, thus arriving at the end of the fiber-optic cable at different times.
However, this is not a problem for the majority of today’s graded-index multimode fiber-optic cable.
“Fiber optics can be utilized for any type of digital signal transmission. RF or any type of video requires an analog-to-digital converter to manipulate signals then convert them back to analog,” adds Luft. “Installers can consider using fiber-optic cable when: long-distance runs are required, electrical or electromagnetic interference is possible, power is not carried over the cable, or bandwidth is an issue.”
No matter what the video application, there is a cable that will fit the bill. However, knowing which one to use requires a combination of cable knowledge and experience. Novice installers may feel intimidated in this regard, but should always remember they can refer to their regular or local cable supplier(s). They can provide sound advice and engineering help.
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