Bulking Up Surveillance

Fiber plays key role in securing cabling distances

• By Mark S. Wilson
• Sep 01, 2010

With the transition from analog to digital video surveillance marching forward, there remains a crucial requirement for reliable transmission of the video signal -- especially during today’s period of coexistence. With many legacy installations, coaxial cable is used to transmit images from a camera for monitoring or recording, or both.

Coax has its limitations, including restricted transmission distance, signal degradation over long cable runs and interference.

Networking and digital and IP technology have ushered in Cat-5/unshielded twisted pair cables and high-speed Ethernet, employing IP to carry the digitized video images. In some installations, wireless transmission -- such as radio frequency, microwave, Wi-Fi and mesh networks -- plays a role. Most enterprise security video designs are not totally wireless.

Instead, the technology is applied to meet certain geographic or operational challenges.

Finally, there is fiber-optic cabling, with its interference immunity, better inherent security, robust cabling distances and huge bandwidth capability.

With all these choices, security end users, designers, integrators and installers must consider and balance the methods with the needed functionality of cameras in regard to maximum cable run distances, power requirements, installation issues, installation time, quality of video, integration with other systems and cost.

Coax Can’t Go the Distance
Coaxial cabling has, for years, been the traditional transmission method of video surveillance traffic. The presence of a coax BNC connector on nearly every security camera underlines this traditional method for signal transmission. The most common coax cable is RG-59U. It provides what many believe is an acceptable quality video path from a camera to the head-end out to 750 feet.

When it comes to powering the camera, many installations employ a “Siamese” cable -- a single RG- 59U wedded to an attached 18/2 cable for both power and video. Still, some distances will increase voltage drop, and it is necessary to select a power supply and cabling that match necessary voltage to distances. Today, when it comes to new and upgraded installations with scores of cameras, a minority uses coaxial while a majority boast Cat-5/UTP and fiber optics.

In some ways, the security shift has been spurred by the popularity of local area networks in most enterprises.

Information technology’s means of transmission gravitated to Cat-5/UTP wiring, as well as fiber optics, often as an overall communications backbone.

Cameras can be more easily installed using existing UTP cabling or fiber previously laid for enterprise network use. Corporate and government IP-based platforms have accelerated the transition.

That naturally has swung security to such designs, especially when it involves video surveillance. UTP cabling is lighter and easier to install, which lowers end-user installation costs, and the material itself is less expensive than comparable lengths of RG-59U. However, there still remain challenges and costs when pushing analog video signals through UTP cable. It requires conversion of the camera’s unbalanced BNC output into a balanced signal that can be carried on one pair of the UTP. When reaching a head-end or recorder, the signal must be reconverted to handle a standard BNCtype connector.

This requires the use of a balun, which is a device that connects a balanced line to an unbalanced line.

It allows one impedance value to be transmitted over a cable that uses a different impedance value. A video balun lets users send video signals over a cable not meant for video. A common situation involving video baluns is use with Cat-5 cable. Coax cable, which transmits video, has an impedance of 75 ohm, while Cat-5 has an impedance of 100 ohm.

Thus, baluns convert the original impedance to the impedance of the cable and back. They are used in pairs; one on each end of the cable. Transmitting video over Cat-5 without the use of video baluns produces ghosting images due to delays in the signal.

Both passive and active baluns are available. Passive baluns convert the signal while active baluns impart an amplification method to increase transmission distance. UTP/balun uses a single pair of a typical four-pair cable to handle the video so three pairs can potentially provide power and pan/tilt/ zoom from a head end to a camera. Such combinations of baluns are called hubs.

How Fiber Optics Help
Fiber-optic technology, a method of sending and receiving information over great distances using light as the carrier, boasts significant advantages.

The advantages of fiber-optic technology include better quality transmission; no interference from lightning strikes, short circuits, “cross talk,” EMI or RFI; high voltages in fluorescent lights, card access door strikes and outdoor lighting systems; a light weight; stability within a wide temperature range; long service life; more security (they are not easily tapped into or interfered with); high bandwidth; and tech growth -- ongoing developments will increase the amount of data transmitted.

Considering Transmission Loss
Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam -- or signal -- with respect to the distance traveled through a transmission medium. It is far less than the equivalent loss in copper cables, leading to long-haul fiber connections with repeater distances of 43 to 93 miles.

There is no doubt that fiber optics can handle massive amounts of digital information across vast distances, securely and with immunity to interference.

Such functionality is built into fiber. A cross section of fiber cable shows a Kevlar inner wrap. Because of this strong nonmetallic component, the cable cannot carry lightning pulses or transient voltages from an outdoor camera into a facility. Plus, within the fiber core, which is composed of glass strands, a blinking LED or laser light is unaffected by electrical and radio frequency anomalies.

With fiber, physical security can have its own strands in the shared fiber bundle, thus achieving a stand-alone posture while also being part of the overall enterprise infrastructure.

Fiber-optic cabling comes in two basic types: multimode and single mode. Multimode fiber has a core size of either 50 or 62.5 microns and commonly provides connections between telecommunications systems within a building or campus. Preferred for most physical security applications, multimode uses lowcost LEDs or inexpensive lasers for transmission. It is easier to terminate and test. However, multimode has a distance limitation -- usually out to three miles -- as compared to single-mode. The latter fiber, with a core size of 7 to 10 microns, typically handles longer distances of more than 50 miles in highbandwidth applications.

Fiber is superior to copper cabling in all performance measures. Available bandwidth of standard multimode fiber is estimated at 45 times that of Cat-5 UTP, while the maximum bandwidth capacity of single-mode fiber has yet to be reached, according to fiber-optic experts.

This is especially important when scores of cameras can transmit their signals over only one or two fiber strands.

Whatever the mode, fiber knocks out Cat-5/UTP. But even though IP-based video is gaining users, there remains a serious distance limitation with UTP cabling infrastructure, hindering placement of cameras.

For example, if a camera is located 1,000 feet from the head end, without any active signal conditioning at some cost, about 37 percent of the information will be lost in transmission, not counting the need and cost for signal amplification, ground fault correction and surge protection.

Opening the Application Doorway
Almost unlimited capabilities exist for security video transmission and PTZ controls. In addition, since a single-fiber strand offers bidirectional signaling, one fiber between two points can carry multiple streams of security video in one direction, while PTZ control can go in the opposite direction, all simultaneously.

Fiber within most buildings is multimode. Some infrastructures have a combination of multimode and single mode.

No matter the mode, there needs to be a way to convert the video signal over to an optical format and back again. Therefore, devices that are part of a fiber-optics transmission system, including receivers and transmitters, can be combined into transceivers, video-to-fiber converters, connectors and adapters.

Fiber connectors come in several common styles, such as ST (round), SC (square) and LC (square). Devices for interfacing physical security equipment to fiber-optic links usually can be ordered with either the ST or SC connector.

Various adapters convert connections, such as connecting an ST video fiber encoder to an SC connector on a network fiber patch panel.

When implementing a coexistence system of analog and digital IP, consider the cost of analog to fiber. However, the increasing speed of an organization’s migration to IP will continue to change that equation.

For example, in addition to providing a means for transparently connecting one type of media to another, media conversion provides a cost-effective method for integrating a hybrid video security system into one seamless and manageable whole. Cost savings can be realized thanks to an existing, analogbased security video infrastructure, while coexisting with the latest technology of IP-based cameras for video capture, storage or analysis and for expanded application of megapixel and HD cameras at added locations.

In coexisting analog/IP security video applications and when all-digital and IP environments ultimately take over, fiber optics lights the way.

This article originally appeared in the September 2010 issue of Security Today.