Written 5

Chapter 6 Analog Video, Voice, and Control Signal Transmission

CONTENTS

6.1 Overview 6.2 Base-band Signal Analysis

6.2.1 Video Picture Signal 6.2.2 Video Synchronization Signal 6.2.3 Voice Signal 6.2.4 Control Data Signals 6.2.5 Modulation and Demodulation 6.2.6 Signal Bandwidth

6.3 Wired Video Transmission 6.3.1 Coaxial Cable

6.3.1.1 Unbalanced Single-Conductor Cable

6.3.1.2 Connectors 6.3.1.3 Amplifiers

6.3.2 Balanced Two-Conductor Twin-axial Cable Transmission 6.3.2.1 Indoor Cable 6.3.2.2 Outdoor Cable 6.3.2.3 Electrical Interference 6.3.2.4 Grounding Problems 6.3.2.5 Aluminum Cable 6.3.2.6 Plenum Cable

6.3.3 Two-Wire Cable Unshielded Twisted Pair (UTP) Transmission 6.3.3.1 Balanced 2-Wire Attributes 6.3.3.2 The UTP Technology 6.3.3.3 UTP Implementation with Video,

Audio, and Control Signals 6.3.3.4 Slow-Scan Transmission

6.3.4 Fiber-Optic Transmission 6.3.4.1 Background 6.3.4.2 Simplified Theory 6.3.4.3 Cable Types

6.3.4.3.1 Multimode Step-Index Fiber

6.3.4.3.2 Multimode Graded-Index Fiber

6.3.4.3.3 Cable Construction and Sizes

6.3.4.3.4 Indoor and Outdoor Cables

6.3.4.4 Connectors and Fiber Termination 6.3.4.4.1 Coupling Efficiency 6.3.4.4.2 Cylindrical and Cone

Ferrule Connector 6.3.4.4.3 Fiber Termination Kits 6.3.4.4.4 Splicing Fibers

6.3.4.5 Fiber-Optic Transmitter 6.3.4.5.1 Generic Types 6.3.4.5.2 Modulation Techniques 6.3.4.5.3 Operational Wavelengths

6.3.4.6 Fiber-Optic Receiver 6.3.4.6.1 Demodulation

techniques 6.3.4.7 Multi-Signal, Single-Fiber

Transmission 6.3.4.8 Fiber Optic—Advantages/

Disadvantages 6.3.4.8.1 Pro 6.3.4.8.2 Con

6.3.4.9 Fiber-Optic Transmission: Checklist 6.4 Wired Control Signal Transmission

6.4.1 Camera/Lens Functions 6.4.2 Pan/Tilt Functions 6.4.3 Control Protocols

6.5 Wireless Video Transmission 6.5.1 Transmission Types 6.5.2 Frequency and Transmission Path

Considerations

145

146 CCTV Surveillance

6.5.3 Microwave Transmission 6.5.3.1 Terrestrial Equipment 6.5.3.2 Satellite Equipment 6.5.3.3 Interference Sources

6.5.4 Radio Frequency Transmission 6.5.4.1 Transmission Path Considerations 6.5.4.2 Radio Frequency Equipment

6.5.5 Infrared Atmospheric Transmission 6.5.5.1 Transmission Path Considerations 6.5.5.2 Infrared Equipment

6.6 Wireless Control Signal Transmission 6.7 Signal Multiplexing/De-multiplexing

6.7.1 Wideband Video Signal 6.7.2 Audio and Control Signal

6.8 Secure Video Transmission 6.8.1 Scrambling 6.8.2 Encryption

6.9 Cable Television 6.10 Analog Transmission Checklist

6.10.1 Wired Transmission 6.10.1.1 Coaxial Cable 6.10.1.2 Two-Wire UTP 6.10.1.3 Fiber-Optic Cable

6.10.2 Wireless Transmission 6.10.2.1 Radio Frequency (RF) 6.10.2.2 Microwave 6.10.2.3 Infrared

6.11 Summary

6.1 OVERVIEW

Closed circuit television (CCTV) and open circuit tele- vision (OCTV) video signals are transmitted from the camera to a variety of remote monitors via some form of wired or wireless transmission channel. Control, communications, and audio signals are also transmitted depending on the system. This chapter covers most of the analog techniques for transmitting these signals. Chapter 7 describes the techniques for transmission of digital signals. Analog transmission is still critically important because of the immense installed base of analog equipment in the security field. These video systems are in operation, and will remain so for many years to come.

In its most common form, the video signal is transmitted at base-band frequencies over a coaxial cable. This chapter identifies techniques and problems associated with trans- mitting video and other signals from the camera site to the remote monitoring location using wired copper-wire and fiber optics, and through-the-air wireless transmission.

Electrical-wire techniques include coaxial cable and two- wire unshielded twisted-pair (UTP). Coaxial cable is suit- able for all video frequencies with minimum distortion or attenuation. Two-wire UTP systems using standard con- ductors (intercom wire, etc.) use special transmitters and

receivers that preferentially boost the high video frequen- cies to compensate for their loss over the wire length.

Faithful video signal transmission is one of the most important aspects of a video system. Each color video channel requires approximately a 6 MHz bandwidth. Monochrome picture transmission needs only a 4.2 MHz bandwidth. Figure 6-1 shows the single-channel video bandwidth requirements for monochrome and color sys- tems.

Using information from other chapters, it is not diffi- cult to specify a good lens, camera, monitor, and video recorder to produce a high-quality picture. However, if means of transmission does not deliver an adequate signal from the camera to the monitor, recorder, or printer, an unsatisfactory picture will result. The final picture is only as good as the weakest link in the system and it is often the transmission means. Good signal transmission requires that the system designer and installer choose the best trans- mission type, and use high-quality materials, and practices professional installation techniques. A poor transmission system will degrade the specifications for camera, lens, monitoring, and recording equipment.

Fiber optics offers a technology for transmitting high- bandwidth, high-quality, multiplexed video pictures, and audio and control signals over a single fiber. Fiber-optic technology has been an important addition to video sig- nal transmission means. The use of fiber-optic cable has significantly improved the picture quality of the transmit- ted video signal and provided a more secure, reliable, and cost-effective transmission link. Some advantages of fiber optics over electrical coaxial-cable or two-wire UTP systems include:

• high bandwidth providing higher resolution or simulta- neous transmission of multiple video signals;

• no electrical interference to or from other electrical equipments or sources;

• strong resistance to tapping (eavesdropping), thereby providing a secure link; and

• no environmental degradation: unharmed by corrosion, moisture, and electrical storms.

Wireless transmission techniques use radio frequencies (RF) in the very high frequency (VHF) and ultra high frequency (UHF) bands, as well as microwave frequen- cies at 900 MHz, 1.2 GHz, and 2.4 GHz and 5.8 GHz in the S and X bands (2–50 GHz). Low-power microwave and RF systems can transmit up to several miles with excellent pic- ture quality, but the higher power systems require an FCC (Federal Communications Commission) license for oper- ation. Wireless systems permit independent placement of the CCTV camera in locations that might be inaccessible for coaxial or other cables.

Cable-less video transmission using IR atmospheric propagation is discussed. Infrared laser transmission requires no FCC approval but is limited in range depend- ing on visibility. Transmission ranges from a few hundred

Analog Video, Voice, and Control Signal Transmission 147

VIDEO INFORMATION (AMPLITUDE MODULATION)

SOUND CENTER

FREQUENCY

6.00

4.5

3.58 1.25

.25

RELATIVE POWER

FREQUENCY (MHz)

COLOR SUBCARRIER

PICTURE CARRIER

1.0

1 2 3 4 5 6 0

AUDIO INFORMATION (FREQUENCY MODULATION)

FIGURE 6-1 Single channel CCTV bandwidth requirements

feet in poor visibility to several thousand feet or even many miles in good visibility.

Infrared is capable of bidirectional communication; control signals are sent in the opposite direction to the video signal and audio is sent in both directions.

The wired and wireless transmission techniques outlined above account for the majority of transmission means from the remote camera site to the monitoring site. There are, however, many instances when the video picture must be transmitted over very long distances—tens, hundreds, or thousands of miles, or across continents. These are accom- plished using digital techniques (Chapter 7). Two-wire, coaxial, or fiber-optic cables for real-time transmission are often not practical in metropolitan areas where a video picture must be transmitted from one building to another building through congested city streets not in sight of each other.

A technique developed in the 1980s for transmitting a video picture anywhere in the world over telephone lines or any two-wire network is called “slow-scan video transmission.” This technique uses a non-real-time two- wire technology that permits the transmission of a video picture from one location to any other location in the world, providing that a two-wire or wireless voice-grade link (telephone line) is available. This system was the forerunner to the present Internet, intranet, and World Wide Web (WWW).

The slow-scan system took a real-time camera video signal and converted into a non-real-time signal and transmitted it at a slower frame rate over any audio com- munications channel (3000 Hz bandwidth). Unlike con- ventional video transmission, in which a real-time signal changed every 1/30th of a second, the slow-scan transmis- sion method sent a single snapshot of a scene over a time period of 1–72 seconds depending on the resolution spec- ified. This effect is similar to that of opening your eyes once every second or once every minute or somewhere in between. When used with an alarm intrusion or VMD the slow-scan equipment began sending pictures, once every few seconds at low resolution (200 TV lines), or every 32 seconds at high resolution (500 TV lines).

A quantum change and advancement has occurred in the video surveillance industry in the past five years. Computer based systems now use digital techniques and equipments from the camera, transmission means, switch- ing and multiplexing equipment, to the DVRs, solid-state LCD, and plasma monitors. The most dramatic change, however, has been in the use of digital transmission (Chapter 7). Now with the Internet and WWW, and digital signal compression a similar function but much improved transmission is accomplished over any wired or wireless network.

A basic understanding of the capabilities of the afore- mentioned techniques, as well as the advantages and

148 CCTV Surveillance

disadvantages of different transmission means, is essen- tial to optimize the final video picture and avoid costly retrofits. Understanding the transmission requirements when choosing the transmission means and hardware is important because it constitutes the most labor-intensive portion of the video installation. Specifying, installing, and testing the video signal and communication cables for intra-building and inter-building wiring represents the major labor cost in the video installation. If the incorrect cable is specified and installed, and must be removed and replaced with another type, serious cost increases result. In the worst situation, where cables are routed in under- ground outdoor conduits, it is imperative to use the cor- rect size and type of cable so as to avoid retrenching or replacing cables.

6.2 BASE-BAND SIGNAL ANALYSIS

The video signal generated by the analog camera is called the “base-band video signal.” It is called base-band because it contains low frequencies, from 30 Hz for NTSC (25 hertz for CCIR) to 6 MHz. To accomplish fiber-optic transmis- sion and wireless RF, microwave, and IR transmission the base-band signal is modulated with a carrier frequency.

The monochrome or color video signal is a complex analog waveform consisting of the picture information (intensity and color) and synchronizing timing pulses. The waveform was defined in specified by the SMPTE. The full specifications are contained in standards RS-170, RS-170A, and RS-170RGB.

6.2.1 Video Picture Signal

For a monochrome camera the picture information is contained in the single amplitude modulated (AM) intensity waveform. The video signal amplitude for full monochrome and color is 1 volt peak to peak. For a color camera the information is contained in three color wave- forms containing the red, green, and blue color contents of the scene. The three colors can faithfully reproduce the color picture. The color signal from the camera sen- sor can be modified in two different forms: (1) composite video, (2) Y (intensity), C (color), and (3) red (R), green (G), blue (B). The monochrome and color video signals are described in Chapter 5.

6.2.2 Video Synchronization Signal

The video synchronization signals consist of vertical field and frame timing pulses, and horizontal line timing pulses. The NTSC standard field and frame timing pulses occur at 1/60 second. and 1/30 second intervals respectively.

The horizontal line timing pulses occur at 63.5 microsec- ond intervals. The CCIR/PAL vertical standard timing is 1/50 second, 1/25 second, and 64 microseconds. The mag- nitude of these timing pulses is shown in Chapter 5.

6.2.3 Voice Signal

In the NTSC standard, the voice and sound information is contained in a sub-carrier centered at 4.5 MHz and at 4.5, 5.5, 6.0 and 6.5 MHz in the CCIR/PAL systems. The signal is frequency modulated (FM) for high fidelity reproduction.

6.2.4 Control Data Signals

While not generating part of the standard NTSC signal, command and control data can be added to the signal. The bits and bytes of digital information are handed dur- ing the vertical retrace times between frames and fields. Camera control (on/off, etc.), lens control (focus, zoom, iris control), and camera platform control (pan, tilt, pre- sets, etc.) signals are digitally controlled to perform these functions.

6.2.5 Modulation and Demodulation

To accomplish fiber-optic transmission, the base-band video signal is converted to an FM signal. For RF transmis- sion the base-band video signal is frequency modulated with the RF of the carrier and 928 MHz (also 435, 1200, 1700 MHz and others). For microwave transmission the base-band is modulated with a camera frequency of 2.4 and 5.8 GHz.

6.2.6 Signal Bandwidth

The base-band color video signal for NTSC is 30 Hz–6 MHz (4 MHz for monochrome), and 25 Hz–7MHz for CCIR/PAL.

6.3 WIRED VIDEO TRANSMISSION

6.3.1 Coaxial Cable

Coaxial cable is used widely for short to medium dis- tances (several hundred to several thousand feet) because its electrical characteristics best match those required to transmit the full-signal bandwidth from the camera to the monitor. The video signal is composed of slowly vary- ing (low-frequency) and rapidly varying (high-frequency) components. Most wires of any type can transmit the low

Analog Video, Voice, and Control Signal Transmission 149

frequencies (20 Hz to a few thousand Hz); practically any wire can carry a telephone conversation. It takes the special coaxial-cable configuration to transmit the full spectrum of frequencies from 20 Hz to 6 MHz without attenuation, as required for high-quality video pictures and audio.

There are basically two types of coaxial and two types of twin-axial cable for use in video transmission systems:

1. 75-ohm unbalanced indoor coaxial cable 2. 75-ohm unbalanced outdoor coaxial cable 3. 124-ohm balanced indoor twin-axial cable 4. 124-ohm balanced outdoor twin-axial cable.

The cable construction for the coaxial and twin-axial types are shown in Figure 6-2. The choice of a particular coax- ial cable depends on the environment in which it will be used and the electrical characteristics required. By far the most common coaxial cables are the RG59/U and the RG11/U, having a 75-ohm impedance. For short camera- to-monitor distances (a few hundred feet), preassembled or field-terminated lengths of RG59/U coaxial cable with BNC connectors at each end are used. The BNC con- nector is a rugged video and RF connector in common use for many decades and the connector of choice for all base-band video connections. Short preassembled lengths of 5, 10, 25, 50, and 100 feet, with BNC-type connectors attached, are available. Long cable runs (several hundred

feet and longer) are assembled in the field, made up of a single length of coaxial cable with a connector at each end. For most interior video installations, RG59/U (0.25 inch diameter), or RG11/U (0.5 inch diameter), 75-ohm unbalanced coaxial cable is used. When using the larger diameter RG11/U cable, a larger UHF-type connector is used. When a long cable run of several thousand feet or more is required, particularly between several buildings, or if electrical interference is present, the balanced 124 - ohm coaxial cable or fiber-optic cable is used. When the camera and monitoring equipments are in two different buildings, and likely at different ground potentials, an unwanted sig- nal may be impressed on the video signal which shows up as an interference (wide bars on the video screen) and makes the picture unacceptable. A two-wire balanced or fiber-optic cable eliminates this condition.

Television camera manufacturers generally specify the maximum distance between camera and monitor over which their equipment will operate when interconnected with a specific type of cable. Table 6-1 summarizes the transmission properties of coaxial and twin-axial cables when used to transmit the video signal.

In applications with cameras and monitors sepa- rated by several thousand feet, video amplifiers are required. Located at the camera output and/or some- where along the coaxial-cable run, they permit increasing

CABLE IMPEDANCE: 75 ohms

INTERCONNECTING SCHEMATIC

CAMERA

MONITOR

JACKET OUTER

FLEXIBLE

POLYPROPYLENE

CONDUCTOR CENTER

DIELECTRIC FOAM

GROUND LEAD COPPER SHIELDING

COAXIAL (UNBALANCED)

TYPES: RG59/U, RG11/U, RG8/U

COPPER

TWINAXIAL (BALANCED)

FIGURE 6-2 Coaxial-twin-axial cable construction

150 CCTV Surveillance

CABLE ONLY COAXIAL

TYPE

MAXIMUM RECOMMENDED CABLE LENGTH (D )

RG59/U

RG6/U

RG11/U

750

1,500

1,800

230

455

550

CABLE WITH AMPLIFIER

FEETS

3,400 1,035

4,800

6,500 1,980

NOTE: IMPEDANCE FOR ALL CABLES = 75 ohms

D

RG59 MINI

CONDUCTOR (GAUGE)

NOMINAL DC RESISTANCE (ohms/1000 ft)

22 SOLID COPPER

20 SOLID COPPER

10.5

14 SOLID COPPER 1.24

41.0

18 SOLID COPPER 6.5

200 800 250

CAMERA MONITOR

METER FEETS METER

61

1,465

Table 6-1 Coaxial Cable Run Capabilities

the camera-to-monitor distance to 3400 feet for RG59/U cable and to 6500 feet for RG11/U cable.

The increased use of color television in security appli- cations requires the accurate transmission of the video signal with minimum distortion by the transmitting cable. High-quality coaxial-cable, UTP, and fiber-optic installa- tions satisfy these requirements.

While a coaxial cable is the most suitable hard-wire cable to transmit the video signal, video information transmitted through coaxial cable over long distances is attenuated differently depending on its signal frequencies. Figure 6-3 illustrates the attenuation as a function of distance and frequency as exhibited by standard coaxial cables.

The attenuation of a 10 MHz signal is approximately three times greater than that of a 1 MHz signal when using a high-quality RG11/U cable. In video transmission, a 3000-foot cable run would attenuate the 5 MHz part of the video signal (representing the high-resolution part of the picture) to approximately one-fourth of its original level at the camera; a 1 MHz signal would be attenuated to only half of its original level. At frequencies below 500 kHz, the attenuation is generally negligible for these distances. This variation in attenuation as a function of frequency has an adverse effect on picture resolution and color quality. The signal deterioration appears on monitors in the form of less definition and contrast and poor color rendition. For example, severe high-frequency attenuation of a signal depicting a white picket fence against a dark background

would cause the pickets to merge into a solid, smearing mass, resulting in less intelligence in the picture.

The most commonly used standard coaxial is RG59/U, which also has the highest signal attenuation. For a 6 MHz bandwidth, the attenuation is approximately 1 dB per 100 feet, representing a signal loss of 11%. A 1000-foot run would have a 10 dB loss—that is, only 31.6% of the video signal would reach the monitor end.

In a process called “vidi-plexing,” special CCTV cameras transmit both the camera power and the video signal over a single coaxial cable (RG59/U or RG11/U). This single- cable camera reduces installation costs, eliminates power wiring, and is ideal for hard-to-reach locations, temporary installations, or camera sites where power is unavailable.

6.3.1.1 Unbalanced Single-Conductor Cable

The most widely used coaxial cable for video security trans- mission and distribution systems is the unbalanced coaxial cable, represented by the RG59/U or RG11/U configura- tions. This cable has a single conductor with a characteris- tic impedance of 75 ohms, and the video signal is applied between the center conductor and a coaxial braided or foil shield (Figure 6-2).

Single-conductor coaxial cables are manufactured with different impedances, but video transmission uses only the 75-ohm impedance, as specified in EIA standards. Other cables that may look like the 75-ohm cable have a different electrical impedance and will not produce an acceptable

Analog Video, Voice, and Control Signal Transmission 151

ATTENUATION (dB/100 ft)

100 20 30 40 50 FREQUENCY (MHz)

RG11/URG6/U

FIBER OPTIC CABLE

0

RG59/U 1.50

1.25

1.00

0.75

0.50

0.25

SOLID POLYETHYLENE OUTDOORS

FOAM RG11/U *

BALANCED VIDEO PAIR

* PREFERRED DIELECTRIC: CELLULAR (FOAM) POLYETHYLENE INDOORS,

16 GAUGE

FIGURE 6-3 Coaxial cable signal attenuation vs. frequency

television picture when used at a distance of 25 or 50 feet or more.

The RG59/U and RG11/U cables are available from many manufacturers in a variety of configurations. The primary difference in construction is the amount and type of shielding and the insulator (dielectric) used to isolate the center conductor from the outer shield. The most common shields are standard single copper braid, double braid, or aluminum foil. Aluminum foil–type should not be used for any CCTV application. It is used only for cable television. Common dielectrics are foam, solid plastic, and air, the latter having a spiral insulator to keep the center conductor from touching the outer braid. The cable is called unbalanced, because the signal current path travels in the forward direction from the camera to the monitor on the center conductor and from the monitor back to the camera again on the shield, which produces a voltage difference (potential) across the outer shield. This current (and voltage) has the effect of unbalancing the electrical circuit.

For short cable runs (a few hundred feet), the delete- rious effects of the coaxial cable—such as signal attenu- ation, hum bars on the picture, deterioration of image resolution, and contrast—are not observed. However, as the distance between the camera and monitor increases to 1000–3000 feet, all these effects come into play. In particular, high-frequency attenuation sometimes requires

equalizing equipment in order to restore resolution and contrast.

Video coaxial cables are designed to transmit maxi- mum signal power from the camera output impedance (75 ohms) with a minimum signal loss. If the cable char- acteristic impedance is not 75 ohms, excessive signal loss and signal reflection from the receiving end will occur and cause a deteriorated picture.

The cable impedance is determined by the conductor and shield resistance of the core dielectric material, shield construction, conductor diameter, and distance between the conductor and the shield. As a guide, resistance of the center conductor for an RG59/U cable should be approximately 15 ohms per 1000 feet, and for an RG11/U cable, approximately 2.6 ohms per 1000 feet. Table 6-2 summarizes some of the characteristics of the RG59/U and RG11/U coaxial cables.

6.3.1.2 Connectors

Coaxial cables are terminated with several types of con- nectors: the PL-259, used with the RG11/U cable, and the BNC, used with the RG59/U cable. The F-type is an RF connector used in cable television systems. Figure 6-4 illustrates these connectors.

The BNC has become the connector of choice in the video industry because it provides a reliable connection

152 CCTV Surveillance

CABLE TYPE

ATTENUATION

RG59/U

RG6/U

RG11/U

2546 *

100 ft 200 ft 300 ft 400 ft 1500 ft500 ft 2000 ft

RG179B/U

3.0

2.4

1.53

4.0

3.2

2.04

8.0

5.1 10.2

dB LOSS

% SIGNAL REMAINING

1 2 3 4.5 6 8 10.5 14 20

90 80 60 50 30 20

(dB) @ 5–10 MHZ

2422/UL1384 * 11.9

5.5

6.0

18.8

7.3

8.0

39.6

18.2

20.0

79.2

36.4

40.0

10.0 20.0

5.2 13.0 26.0

16.0

3.9RG59 MINI

* MOGAMI NOTE: IMPEDANCE FOR ALL CABLES = 75 ohms

SIAMESE: RG59 (2) #22AWG

20.010.0

5.0

4.0

2.55

19.8

9.1

10.0

6.5

5.04.03.0

2.0

1.6

1.02

7.9

3.6

4.0

2.6

2.0

1.0

.51

1.82

.8

3.96

2.0

1.3

1.0

1000 ft

59.4

27.3

30.0

15.0

12.0

19.5

15.0

7.66

70 40 10

Table 6-2 Coaxial Cable Attenuation vs. Length

RCA BNC UHF

SMA F SIAMESE POWER/BNC

FIGURE 6-4 RCA, BNC, F, SMA, UHF and siamese cable connectors

with minimum signal loss, has a fast and positive twist-on action, and has a small size, so that many connectors can be installed on a chassis when required. There are essen- tially three types of BNC connectors available: (1) solder, (2) crimp-on, and (3) screw-on.

The most durable and reliable connectors are the sol- der and crimp-on. They are used when the connector is installed at the point of manufacture or in a suitably equipped electrical shop. The crimp-on and screw-on types are the most commonly used in the field, during installa- tion and repair of a system. Either type can be successfully assembled with few tools in most locations. The crimp-on type uses a sleeve, which is attached to the cable end after the braid and insulation have been properly cut back; it is crimped onto the outer braid and the center conductor with a special crimping plier. When properly installed, this cable termination provides a reliable connection.

To assemble the screw-on type, the braid and insulation are cut back and the connector slid over the end of the cable and then screwed on. This too is a fairly reliable type of connection, but it is not as durable as the crimp-on type, since it can be inadvertently unscrewed from the end of the cable. The screw-on termination is less reliable if the cable must be taken on or off many times.

6.3.1.3 Amplifiers

When the distance between the camera and the monitor exceeds the recommended length for the RG59/U and RG11/U cables, it is necessary to insert a video amplifier to boost the video signal level. The video amplifier is inserted at the camera location or somewhere along the coaxial

Analog Video, Voice, and Control Signal Transmission 153

cable run between the camera and the monitor location (Figure 6-5).

The disadvantage of locating the video amplifier some- where along the coaxial cable is that since the amplifier requires a source of AC (or DC) power, the power source must be available at its location. Table 6-1 compares the cable-length runs with and without a video amplifier. Note that the distance transmitted can be increased more than fourfold with one of these amplifiers.

When the output from the camera must be distributed to various monitors or separate buildings and locations, a distribution amplifier is used (see Figure 6-5). This amplifier transmits and distributes monochrome and color video signals to multiple locations. In a quad unit, a single video input to the amplifier results in four identi- cal, isolated video outputs capable of driving four 75-ohm RG59/U or RG11/U cables. The distribution amplifier is in effect a power amplifier, boosting the power from the single camera output so that multiple 75-ohm loads can be driven. A potential problem with an unbalanced coaxial cable is that the video signal is applied across the single inner conductor and the outer shield, thereby impressing a small voltage (hum voltage) on the signal. This hum

voltage can be eliminated by using an isolation amplifier, a balanced coaxial cable, or fiber optics.

6.3.2 Balanced Two-Conductor Twin-axial Cable Transmission

Balanced twin-axial cables are less familiar to the CCTV industry than the unbalanced cables. They have a pair of inner conductors surrounded by insulation, a coaxial-type shield, and an outer insulating protective sheath has a characteristic impedance of 124 ohms. They have been used for many years by telephone industry for transmitting video information and other high-frequency data. These cables have an outside diameter (typically 0.5 inch) and their cost, weight, and volume are higher than those of an unbalanced cable. Since the polarity on balanced cables must be maintained, the connector types are usually polar- ized (keyed). Figure 6-6 shows the construction and con- figuration of a balanced twin-axial cable system.

The primary purposes for using balanced cable are to increase transmission range and to eliminate the pic- ture degradation found in some unbalanced applications. Unwanted hum bars (dark bars on the television picture)

CAMERA AMPLIFIER MONITOR

PRINTER

EXTENDED RANGE

DISTRIBUTION TO MULTIPLE RECEIVING EQUIPMENT

* EQUIPMENT IN THE SAME OR MULTIPLE LOCATIONS

MONITOR

SWITCHER

SCENE

SCENE

MONITOR

MONITOR

MONITOR

MONITOR

MONITOR

DISTRIBUTION AMPLIFIER

*

*

*

*

COAX COAX

COAX CAMERA

VIDEO

COAX

DVR / VCR

DVR / VCR

DVR / VCR

DVR / VCR

DVR / VCR

FIGURE 6-5 Video amplifier to extend range and/or distribute signal

154 CCTV Surveillance

OUTER INSULATED

JACKET

FOAM INSULATION

METALLIC BRAID

IMPEDANCE: 124 ohms

INTERCONNECTING SCHEMATIC

BALANCED TRANSMITTING TRANSFORMER

124 ohm BALANCED

CABLE

BALANCED RECEIVING

TRANSFORMER

SCENE

CAMERA

DUAL COPPER

CONDUCTORS

MONITOR

FIGURE 6-6 Balanced twin-axial cable construction and interconnection

are introduced in unbalanced coaxial transmission systems when there is a difference in voltage between the two ends of the coaxial cable (see Section 6.3.1.1). This can often occur when two ends of a long cable run are terminated in different buildings, or when electrical power is derived from different power sources—in different buildings or even within the same building.

Since the signal path and the hum current path through the shield of an unbalanced cable are common and result in the hum problem, a logical solution is to provide a separate path for each. This is accomplished by applying the signal between each center conductor of two paral- lel unbalanced cables (Figure 6-6). The shields of the two cables carry the ground currents while the two con- ductors carry the transmitted signal. This technique has been used for many years in the communications indus- try to reduce or eliminate hum. Since the transmitted video signal travels on the inner conductors, any noise or induced AC hum is applied equally to each conductor. At the termination of the run the disturbances are cancelled while the signal is directed to the load unattenuated. This technique in effect removes the unwanted hum and noise signals.

While the balanced transmission line offers many advan- tages over the unbalanced line, it has not been in widespread use in the video security industry. The pri- mary reason is the need for transformers at the camera- sending and monitor-receiving ends, as well as the need for two-conductor twin-axial cable. All three hardware items require additional cost as compared with the unbal-

anced single-conductor coaxial cable. The use of UTP transmission has become a popular replacement for the coaxial cable (Section 6.3.3), or fiber optics, described in Section 6.3.4.

6.3.2.1 Indoor Cable

Indoor coaxial cable is small in diameter (0.25 inch), uses a braided shield, and is much more flexible than out- door cable. To maintain the correct electrical impedance this smaller outside diameter cable requires proportion- ally smaller inner conductors. This decrease in diameter of the cable conductor causes a corresponding increase in the cable signal attenuation and therefore the RG59/U indoor cable cannot be used over long distances. The impedance of any coaxial cable is directly related to the spacing between the inner conductor and the shield; any change in this spacing caused by tight bends, kink- ing, indentations, or other factors will change the cable impedance resulting in picture degradation. Since indoor cabling and connectors need no protection from water, solder, crimp-on, or screw-on connectors can be used.

6.3.2.2 Outdoor Cable

Outdoor video transmission applications put additional physical requirements on the coaxial cable. Environmental factors such as precipitation, temperature changes, humid- ity, and corrosion are present for both above-ground

Analog Video, Voice, and Control Signal Transmission 155

and buried installations. Other above-ground considera- tions include: wind loading, rodent damage, and electrical storm interference. For direct burial applications, ground shifts, damage due to water, and rodent damage are poten- tial problems. Outdoor coaxial cabling is 1/2 inch in diam- eter or larger, since the insulation qualities in outside protective sheathing must be superior to those of indoor cables and their electrical qualities are better than indoor RG59/U cables. Outdoor cables have approximately 16 gauge inner-conductor diameters resulting in much less signal loss than the smaller, approximately 18 gauge cen- ter conductor indoor RG59/U cables. Outdoor cables are designed and constructed to take much more physical abuse than the indoor RG59/U cable. Outdoor cables are not very flexible and care must be taken with extremely sharp bends. As a rule of thumb, outdoor cabling should always be used for cable runs of more than 1000 feet, regardless of the environment.

Outdoor video cable may be buried, run along the ground, or suspended on utility poles. The exact method should be determined by the length of the cable run, the economics of the installation, and the particular environ- ment. Environment is an important consideration.

In locations with severe weather, electrical storms or high winds, it is prudent to locate the coaxial cable under- ground, either direct-buried or enclosed in a conduit. This method isolates the cable from the severe environment, improving the life of the cable and reducing signal loss. In locations having rodent or ground-shift problems, enclos- ing the cable in a separate conduit will protect it. For short cable runs between buildings (less than 600–700 feet) and where the conduit is waterproof, indoor RG59/U cable is suitable.

There are about 25 different types of RG59/U and about 10 different types of RG11/U cable but only a few are suit- able for video systems. For optimum performance, choose a cable that has 95% copper shield or more and a copper or copper-clad center conductor. The copper-clad center conductor has a core of steel and copper cladding, has higher tensile strength, and is more suitable for pulling through conduit over long cable runs. While cable with 65% copper shield is available, 95% shielding or more should be used to reduce and prevent outside electro- magnetic interference (EMI) signals from penetrating the shield, causing spurious noise on the video signal. A coax- ial cable with 95% shield and a copper center conductor will have a loop resistance of approximately 16–57 ohms per 1000 feet.

6.3.2.3 Electrical Interference

For indoor applications, interference and noise can result from the following problems: (1) different ground poten- tials at the ends of the coaxial cable at different video equipment locations in a building, and (2) coaxial cable

near other electrical power distribution equipment or machinery producing high electromagnetic fields.

In outdoor applications, in addition to the above the adverse environmental conditions caused by lightning storms or other high-voltage noise generators, such as transformers on power lines, electrical substations, auto- mobile/truck electrical noise, or other EMI must be considered.

In the case of EMI, a facility site survey should be made of the electromagnetic radiation present in any electrically noisy power distribution equipment. The cables should then be routed away from such equipment so that there is no interference with the television signal.

When a site survey indicates that the coaxial cable must run through an area containing large electrical inter- fering signals (EMI) caused by large machinery, high- voltage power lines, refrigeration units, microwaves, truck ignition, radio or television stations, fluorescent lamps, two-way radios, motor-generator sets, or other sources, a better shielded cable, such as a twin-axial, tri-axial, UTP, or fiber optic cable may be the answer. The tri-axial cable has a center conductor, an insulator, a shield, a second insulator, a second shield, and the normal outer polyethylene or other covering to protect it from the envi- ronment. The double shielding significantly reduces the amount of outside EMI radiation that gets to the center conductor.

The number of horizontal bars on the monitor can indicate where the source of the problem is. If the monitor has six dark bars, multiplying 6 by 60 equals 360, which is close to a 400-cycle frequency. This interference could be caused by an auxiliary motor-generator set often found in large factory machines operating at this frequency. To correct the problem, the cable could be rerouted away from the noise source, replaced with a balanced twin-axial or tri-axial cable, UTP, or for 100% elimination of the problem, upgraded to fiber-optic cable.

If lighting and electrical storms are anticipated and sig- nal loss is unacceptable, outdoor cables must be buried underground and proper high voltage–suppression cir- cuitry must be installed at each end of the cable run and on the input power to the television equipment.

In new installations with long cable runs (several thou- sand feet to several miles) or where different ground volt- ages exist, a fiber-optic link is the better solution, although balanced systems and isolation amplifiers can often solve the problem.

6.3.2.4 Grounding Problems

Ground loops are by far the most troublesome and notice- able video cabling problem (Figure 6-7). Ground loops are most easily detected before connecting the cables, by measuring the electrical voltage between the coaxial-cable shield and the chassis to which it is being connected. If the voltage difference is a few volts or more, there is a

156 CCTV Surveillance

HUM BAR

HUM BAR

HUM BAR

PICTURE TEARING

HUM BAR

FIGURE 6-7 Hum bars caused by ground loops

potential for a hum problem. As a precaution, it is good practice to measure the voltage difference before connect- ing the cable and chassis for systems with a long run or between any two electrical supplies to prevent any damage to the equipment.

Many large multiple-camera systems have some distor- tion in the video picture caused by random or periodic noise or if more severe, by hum bars. The hum bar appears as a horizontal distortion across the monitor at two loca- tions: one-third and two-thirds of the way down the pic- ture. If the camera is synchronized or power-line-locked, the bar will be stationary on the screen. If the camera is not line-locked, the distortion or bar will continuously roll slowly through the picture. Sometimes the hum bars are accompanied by sharp tearing regions across the moni- tor or erratic horizontal pulling at the edge of the screen (Figure 6-7). This is caused by the effect of the high volt- ages on the horizontal synchronization signal. Other symp- toms include uncontrolled vertical rolling of the scene on the screen when there are very high voltages present in the ground loop.

Interference caused by external sources or voltage dif- ferences can often be predicted prior to installation. The hum bar and potential difference between two electri- cal systems usually cannot be determined until the actual installation. The system designer should try to anticipate the problem and, along with the user, be prepared to devote additional equipment and time to solve it. The problem is not related to equipment at the camera or

monitor end or to the cable installed; it is strictly an effect of the particular environment encountered, be it EMI interference or difference in potential between the main power sources at each location. The grounding problem can occur at any remote location, and it can be eliminated inexpensively with the installation of an isolation ampli- fier. Another solution, described in Section 6.3.4, is the use of fiber-optic transmission means, which eliminates electrical connections entirely.

One totally unacceptable solution is the removal of the third wire on a three-pronged electrical plug, which is used to ground the equipment chassis to earth ground. Not only is such removal a violation of local electrical codes and Underwriters Laboratory (UL) recommendations, it is a hazardous procedure. If the earth ground is removed from the chassis, a voltage can appear on the camera, monitor, or other equipment chassis, producing a “hot” chassis that, if touched, can shock any person with 60–70 volts.

When video cables bridge two power distribution systems, ground loops occur. Consider the situation (Figure 6-8) in which the CCTV camera receives AC power from power source A, while some distance away or in a different building the CCTV monitor receives power from distribution system B.

The camera chassis is at 0 volts (connected to electri- cal ground) with reference to its AC power input A. The monitor chassis is also at 0 volts with respect to its AC distribution system B. However, the level of the electri- cal ground in one distribution system may be higher (or lower) than that of the ground in the other system; hence a voltage potential can exist between the two chassis. When a video cable is connected between the two distribution system grounds, the cable shield connects the two chas- sis and an alternating current flows in the shield between the units. This extraneous voltage (causing a ground-loop current to flow) produces the unwanted hum bars in the video image on the monitor.

The second way in which hum bars can be produced on a television monitor is when two equipment chassis are mechanically connected, such as when a camera is mounted on a pan/tilt unit. If the camera receives power from one distribution system and the chassis of the pan/tilt unit is grounded to another system with a different level, a ground loop and hum bars may result. The size and extent of the horizontal bars depends on the severity of the ground potential difference.

6.3.2.5 Aluminum Cable

Although coaxial cable with aluminum shielding provides 100% shielding, it should only be used for RF cable tele- vision (CATV) and master television (MATV) signals used for home video cable reception. This aluminum-shield type should never be used for CCTV for two reasons: (1) it

Analog Video, Voice, and Control Signal Transmission 157

LOCATION A LOCATION B

CAMERA (PAN/ TILT, ETC.)

COAXIAL CABLE

CONTROL WIRE

GROUND

COAXIAL SHIELD

GROUND

117 VAC POWER FROM SYSTEM A

0 VOLTS

LOCATION A GROUND

MONITOR (OR SWITCHER, VCR, PRINTER, ETC.)

VOLTAGE DIFFERENCE

POWER SOURCE A POWER SOURCE B

GROUND SHIELD

COAXIAL 117 VAC POWER FROM SYSTEM B

LOCATION B GROUND

*

*

NOTE: THE VOLTAGE DIFFERENCE BETWEEN GROUND A AND B CAN BE 5–30 VOLTS, CAUSING CURRENT TO FLOW IN THE CABLE SHIELD, HUM BARS AND FAULTY OPERATION

FIGURE 6-8 Two source AC power distribution system

has higher resistance, and (2) it distorts horizontal syn- chronization pulses.

The added resistance—approximately seven times more than that of a 95% copper or copper-clad shield— increases the video cable loop resistance, causing a reduc- tion in the video signal transmitted along the cable. The higher loop resistance means a smaller video signal reaches the monitoring site, producing less contrast and an inferior picture. Always use a good-grade 95% copper braid RG59/U cable to transmit the video signal up to 1000 feet and an RG11/U to transmit up to 2000 feet. Distortion of the horizontal synchronization pulse causes picture tearing on the monitor, depicting straight-edged objects with ragged edges.

6.3.2.6 Plenum Cable

Another category of coaxial cable is designed to be used in the plenum space in large buildings. This plenum cable has a flame-resistant exterior covering and very low smoke emission. The cable can be used in air-duct air-conditioning returns and does not require a metal conduit for added

protection. The cable, designated as “plenum rated,” is approved by the National Electrical Code and UL.

6.3.3 Two-Wire Cable Unshielded Twisted Pair (UTP) Transmission

It is convenient, inexpensive, and simple to transmit the video signal over an existing two-wire system. A stan- dard, twisted pair, two-wire telephone, intercom, or other electrical system with an appropriate UTP transmitter and receiver has the capability to transmit all of the high- frequency information required for an excellent resolu- tion monochrome or color picture. The UTP is a CAT-5, CAT-5e, or CAT-3 cable. The higher the level of CAT (5e) cable the greater the distance. Either a passive (no power required) or an active (12VDC, longer distanced) transmitter/receiver pair can be used. The passive system uses a small transmitter and receiver-one at each end of the pair of wires—and transmits the picture at distances of a few hundred feet to 3000 feet. The active powered system (12VDC) can transmit the video image 8000 feet for monochrome and 5000 feet for color. Picture resolu- tion can be equivalent to that obtained with a coaxial cable

158 CCTV Surveillance

system. The two-wire pair must have a continuous conduc- tive path from the camera to the monitor location. High- frequency emphasis in the transmitter and receiver com- pensate for any attenuation of the high frequencies. The balanced UTP configuration makes the cable immune to most external electrical interference and in many environ- ments the UTP cable can be located in the same conduit with other data cables.

The UTP system must have a conductive (resistive cop- per) path for the two wires. The signal path cannot have electrical switching circuits between the camera and the monitor location; however, mechanical splices and con- nectors are permissible.

The components for the two-wire system can cost more than equivalent coaxial cable since an additional transmit- ter and receiver are required. However, this cost may be small compared with the cost of installing a new coaxial cable from the camera to the monitor location. Figure 6-9 illustrates the block diagram and connections for the UTP, and active transmitter and receiver pair.

6.3.3.1 Balanced 2-Wire Attributes

The UTP provides a technology that can significantly reduce external electrical radiation from causing noise in

the video signal. It also eliminates ground loops present in unbalanced coaxial transmission since isolation designed into the UTP transmitters and receivers.

6.3.3.2 UTP Technology

The UTP technology is based on the concept that any external electrical interference affects each of the two conductors identically so that the external disturbance is canceled and has no effect on the video signal. The trans- mitter unit converts the camera signal 75 ohm impedance to match the UTP 100 ohm CAT-5e impedance and pro- vides the frequency compensation required. The receiver unit amplifies and reconstructs the signal and transmits it over a short distance to the television monitor via 75 ohm coaxial cable. Most active transmitters and receivers have 3 to 5 position dip switches which are set depending on the cable length to optimize the video signal wave- form. Both the transmitter and the receiver are powered by either 12VDC or self-powered from the camera or monitor.

The UTP system can be operated with CAT-3, 5, 5e, and 6 as defined in the TIA/EIA 568b.2 standard. CAT-5e is now used for most new video installations and supercedes the extensively installed CAT-5 cable.

(A) ACTIVE TRANSMITTER (B) ACTIVE RECEIVER

COAX COAX RECEIVERTRANSMITTER

UNSHIELDED TWISTED PAIR

(UTP) CAT-3, 5, 5e

VIDEO VIDEO

CAMERA

MONITOR

75 ohm

100 ohm

75 ohm

FIGURE 6-9 Two wire UTP video transmission system

Analog Video, Voice, and Control Signal Transmission 159

6.3.3.3 UTP Implementation with Video, Audio, and Control Signals

The UTP transmitter is located between the camera and the CAT-5e UTP cable input to transmit video, audio, alarms, and control signals. The receiver is located between the monitor end of the CAT-5e UTP cable and the monitor, recorder, or control console. UTP transmit- ters are small enough to be part of the camera electronics or can be powered by the camera, audio, and/or control electronics (Figure 6-10).

6.3.3.4 Slow-Scan Transmission

The wireless transmission systems described in the pre- vious sections all result in real-time video transmission. A scheme for transmitting the television picture over large distances, even anywhere in the world, uses slow-scan tele- vision transmission (Figure 6-11).

This non-real-time technique involves storing one televi- sion picture frame (snapshot) and sending it slowly over a telephone or other audio-grade network anywhere within a country or to another country. The received picture is reconstructed at the remote receiver to produce a contin- uously displayed television snapshot. Each snapshot takes anywhere from several to 72 seconds to transmit, with a resulting picture having from low to high resolution, depending on the speed of transmission. A TL effect is achieved, and every scene frame is transmitted spaced from several to 72 seconds apart.

Through this operation, specific frames are serially cap- tured, sent down the telephone line, and reconstructed by

the slow-scan system. Once the receiver has stored the dig- ital picture information, if the transmitter is turned off or the video scene image does not change, the receiver con- tinues to display the last video frame continuously (30 fps) as a still image. The image stored in the receiver or trans- mitter changes when the system is commanded, manually or automatically, to take a new snapshot. Figure 6-12 illus- trates the salient difference between real-time and non- real-time television transmission.

Implementation. Figure 6-12 shows the relationship of non-real-time or slow-scan television transmission. At the camera site the first frame starts at time zero (Figure 6-12a), the second frame at 1/30th of a second, and the third frame at 2/30th of a second (the same as for real-time). Before these frames are transmitted over the audio-grade transmission link, the signal is processed at the camera site in a transmitter processor. The processor captures Frame 1 from the camera, that is, it memorizes (digitizes) the CCTV picture. The processor then slowly (at 2 seconds per frame, as shown in Figure 6-12b) trans- mits the video frame, element by element, line by line, until the receiver processor located at the monitor site has accepted all 525 lines in that frame.

The significant difference between real-time and slow- scan transmission is the time it takes to transmit the picture. In the real-time case, it is 1/30th of a second, the real-time of the frame. In the case of the slow-scan (Figure 6-12b), it may take 2, 4, 8, 32, up to 72 seconds to transmit that single frame to the monitor site. Figure 6-13 is a block diagram of a simplex (one-way) slow-scan system.

CAMERA

MICROPHONE

SPEAKER

COMMAND FUNCTIONS

ALARM INPUTS

MICROPHONE

SPEAKER

ALARM OUTPUT DEVICES

COAX COAX VIDEO

TRANSMITTER: • VIDEO • AUDIO • ALARM

RECEIVER: • AUDIO • CONTROL

TRANSMITTER: • AUDIO • CONTROL

• VIDEO • AUDIO • ALARM

• TELEPHONE • TWISTED PAIR (UTP) • SHIELDED 2 WIRE

DEDICATED TWO WIRE SYSTEM

RECEIVER:

FIGURE 6-10 Real-time transmission system with video, audio, and controls

160 CCTV Surveillance

SLOW-SCAN TRANSCEIVER

SLOW-SCAN TRANSCEIVER

MONITOR

DUPLEX (TWO-WAY) NETWORK

CAMERACAMERA

LOCATION 1 LOCATION 2

(A) PICTURE RESOLUTION: 128 × 64 (H × V) FULL PICTURE TRANSMIT TIME: 2.6 SEC

(B) PICTURE RESOLUTION: 256 × 128 (H × V) FULL PICTURE TRANSMIT TIME: 8.0 SEC

(C) PICTURE RESOLUTION: 512 × 256 (H × V) FULL PICTURE TRANSMIT TIME: 31 SEC

NOTE: PICTURE TRANSMIT UPDATE TIME DEPENDS ON MOTION IN PICTURE. MONOCHROME PICTURE.

3000 Hz BANDWIDTH

MONITOR

FIGURE 6-11 Slow-scan video transmission and transmitted pictures over telephone lines

FRAME 1 T = 0

FRAME 2 T = 1/30 SEC

FRAME 3 T = 2/30 SEC

FRAME 1 T = 0

FRAME 2 T = 2 SEC

FRAME 3 T = 4 SEC

CONTINUOUS VIEWING OF MOVING VEHICLE

SNAP SHOTS OF PERSON WALKING

(A) REAL-TIME (30 FPS) (B) SLOW-SCAN

G

G

FIGURE 6-12 Real-time video transmission vs. non-real-time (slow-scan)

Analog Video, Voice, and Control Signal Transmission 161

CAMERA ANALOG/ DIGITAL

CONVERTER

VIDEO FRAME

GRABBER

DIGITAL TELEPHONE

DIALER

ANY DUPLEX AUDIO BANDWITH COMMUNICATIONS LINK

DIGITAL VIDEO

COMPRESSION

DIGITAL TO ANALOG CONVERTER

ALARM INPUT

AUDIO FREQUENCY

DEMODULATOR

ANALOG TO DIGITAL

CONVERTER

DIGITAL VIDEO

DECOMPRESSION

TEMPORARY MEMORY

DIGITAL TO ANALOG CONVERTER

MONITOR

AUDIO DRIVE

AMPLIFIER

NUMBER OF GRAY SCALE

LEVELS

SCAN RATE

LENS

FIGURE 6-13 Slow-scan system block diagram—simplex (one-way)

To increase transmission speed, complex compression and modulation algorithms are used so that only the changing parts of a scene (i.e. the movements) are trans- mitted. Another technique first transmits areas of high scene activity with high resolution and then areas of lower priority with lower resolution. These techniques increase the transmission of the intelligence in the scene. By increasing transmission time of the frame from 1/30th of a second to several seconds, the choice of cable or transmission path changes significantly. For slow-scan it is possible to send the full video image on a twisted-pair or telephone line or any communications channel hav- ing a bandwidth equivalent to audio frequencies, that is, up to only 3000 Hz (instead of a bandwidth up to 4.2 MHz, as needed in real-time transmission). So all exist- ing satellite links, mobile telephones, and other connec- tions can be used. A variation of this equipment for an alarm application can store multiple frames at the trans- mitting site, so if the information to be transmitted is an alarm, this alarm video image can be stored for a few sec- onds (every 1/30 second) and then slowly transmitted to the remote monitoring site frame by frame, thereby trans- mitting all of the alarm frames. Figure 6-14 shows the inter- connecting diagram and controls for a typical slow-scan system.

Resolution, Scene Activity vs. Transmit Time. Transmit time per frame is determined by video picture resolution and activity (motion) in the scene. The larger the number of gray-scale levels and number of colors transmitted, the longer the transmit time per frame of video. If only a few gray-scale levels are transmitted (photocopy quality), or a limited number of colors and a small amount of motion in the scene are present, then there is less picture information to transmit and short (1–8 seconds) transmit times result. High gray-scale levels (256 levels), full color, and motion require more information and longer trans- mission times. Slow-scan transmission is a compromise between resolution and scene activity and required scene update time.

6.3.4 Fiber-Optic Transmission

6.3.4.1 Background

One of the most significant advances in communications and signal transmission has been the innovation of fiber optics. However, the concept of transmitting video signals over fiber optics is not new. The transmission of optical signals in fibers was investigated in the 1920s and 1930s but it was not until the 1950s that Kapany invented the

162 CCTV Surveillance

CAMERA

AC OR DC POWER

• TRANSMIT TIME (1, 2, 4, 8, 16, 32, 64)

• SHADES OF GRAY (16, 32, 64, 128)

POWER AC OR DC

• QUAD OR FULL SCREEN

MONITORTRANSMISSION PATH:

ANY AUDIO GRADE

CHANNEL

MONITOR *

* DUPLEX SYSTEM (2 WAY) USE MONITOR AND CAMERA AT EACH END

• PIXEL RESOLUTION (32, 64, 128, 256, 512)

TALK / VIEW

AUTO ANSWER / TRANSMIT

KEYPAD CONTROLS:

• EXTERNAL DEVICES (VCR, HORN, LIGHTS, ETC.)

TRANSMIT ANSWER /

AUTO

VIEW TALK /

CAMERA

CAMERA

CAMERA 1

2

3

4

CAMERA

CAMERA

CAMERA

CAMERA 1

2

3

4

• CAMERA SELECTOR (4 CAMERAS)

FIGURE 6-14 Slow-scan interconnecting diagram and controls

practical glass-coated (clad) glass fiber and coined the term fiber optics.

Clad fiber was actively investigated in the 1960s by K.C. Kao and G.A. Hockham, researchers at Standard Telecommunications Laboratories in England, who pro- posed that this type of waveguide could form the basis of a new transmission system. In 1967 attenuations through the fiber was more than 1000 dB per kilometer (0.001% trans- mission/km) which were impractical for transmission pur- poses, and researchers focused on reducing these losses. Figure 6-16 shows a comparison of fiber-optic transmission vs. other electrical transmission means. In 1970, investiga- tors Kapron, Keck, and Maurer at Corning Glass Works announced a reduction of losses to less than 20 dB per kilometer in fibers hundreds of meters long. In 1972 Corn- ing announced a reduction of 4 dB per one kilometer of cable, and in 1973 Corning broke this record with a 2 dB per kilometer cable. This low-loss achievement made a rev- olution in transmission of wide-bandwidth, long-distance communications inevitable. In the early 1970s, manufac- turers began making glass fibers that were sufficiently low- loss to transmit light signals over practical distances of hundreds or a few thousand feet.

Broadband fiber-optic components are much more expensive than cable. They should be used when there is a definite need for them. Note also that video signals must be digitized to avoid nonlinear transmitter/receiver effects.

Why use fiber-optic transmission when coaxial cables can provide adequate video signal transmission? Today’s high-performance video systems require greater reliability and more “throughput,” that is, getting more signals from the camera end to the monitor end, over greater distances, and in harsher environments. The fiber-optic transmis- sion system preserves the quality of the video signal and provides a high level of security.

The information-carrying capacity of a transmission line, whether electrical or optical, increases as the carrier frequency increases. The carrier for fiber-optic signals is light, which has frequencies several orders of magni- tude (1000 times) greater than radio frequencies, and the higher the carrier frequency the larger the bandwidth that can be modulated onto the cable. Some transmitters and receivers permit multiplexing multiple television sig- nals, control signals, and duplex audio onto the same fiber optic because of its wide bandwidth.

The clarity of the picture transmitted using fiber optics is now limited only by the camera, environment, and

Analog Video, Voice, and Control Signal Transmission 163

LENS

CAMERA

POWER CONVERTER 117 VAC TO

12 VDC

ELECTRICAL TO OPTICAL SIGNAL

CONVERTER

FIBER OPTIC CABLE OPTICAL TO

ELECTRICAL SIGNAL

CONVERTER

POWER CONVERTER 117 VAC TO

12 VDC

FIBER OPTIC SYSTEM COMPONENTS:

• TRANSMITTER • RECEIVER • FIBER OPTIC CABLE • POWER CONVERTERS (2)

117 VAC POWER

117 VAC POWER

GND 12 VDCGND

OPTICAL CONNECTORS (SMA, SFR, LFR) TRANSMITTER

OPTICAL CONNECTORS (SMA, SFR, LFR)

RECEIVER

MONITOR

COAXIAL CABLE

COAXIAL CABLE

BNC BNCBNC

BNC

12 VDC

FIGURE 6-15 Fiber optic transmission system

monitoring equipment. Fiber-optic systems can transmit signals from a camera to a monitor over great distances— typically several miles—with virtually no distortion or loss in picture resolution or detail. Figure 6-15 shows the block diagram of the hardware required for a fiber-optic system.

The system uses an electrical-to-optical signal con- verter/transmitter, a fiber cable for sending the light signal from the camera to the monitor, and a light-to- electrical signal receiver/converter to transform the signal back to a base-band video signal required by the moni- tor. At both camera and monitor ends standard RG59/U coaxial cable or UTP wire is used to connect the camera and monitor to the system.

A glass fiber optic–based video link offers distinct advantages over copper-wire or coaxial-cable transmission means:

• The system transmits information with greater fidelity and clarity over longer distances.

• The fiber is totally immune to all types of electrical interference—EMI or lightning—and will not conduct electricity. It can touch high-voltage electrical equip- ment or power lines without a problem.

• The fiber being nonconductive does not create any ground loops.

• The fiber can be serviced while the transmitting or receiving equipment is still energized since no electrical power is involved.

• The fiber can be used where electrical codes and com- mon sense prohibit the use of copper wires.

• The cable will not corrode and the glass fiber is unaf- fected by salt and most chemicals. The direct-burial type of cable can be laid in most kinds of soil or exposed to most corrosive atmospheres inside chemical plants or outdoors.

• Since there is no electrical connection of any type, the fiber poses no fire hazard to any equipment or facility in even the most flammable atmosphere.

• The fiber is virtually unaffected by atmospheric condi- tions, so the cable can be mounted aboveground and on telephone poles. When properly applied, the cable is stronger than standard electrical wire or coaxial cable and will therefore withstand far more stress from wind and ice loading.

• Single or multiple fiber-optic cables are much smaller and lighter than a coaxial cable. It is easier to handle and install, and uses less conduit or duct space. A single optical cable weighs 8 pounds per 3300 feet and has an overall diameter of 0.156 inches. A single coaxial cable weighs 330 pounds per 3300 feet and is approximately 0.25 inches in diameter.

164 CCTV Surveillance

• It transmits the video signal more efficiently (i.e. with lower attenuation) and since over distances of less than 50 miles it needs no repeater (amplifier), it is more reliable and easier to maintain.

• It is a more secure transmission medium, since not only is it hard to tap but an attempted tap is easily detected.

The economics of using a fiber-optic system is com- plex. Users evaluating fiber optics should consider the costs beyond those for the components themselves. The small size, lightweight, and flexibility of fiber optics often present offsetting cost advantages. The prevention of unanticipated problems such as those just listed can easily offset any increased hardware costs of fiber-optic systems.

With such rapid advances, the security system designer should consider fiber optics the optimum means to trans- mit high-quality television signals from high-resolution monochrome or color cameras to a receiver (monitor, switcher, recorder, printer, and so on) without degrada- tion. This section reviews the attributes of fiber-optic sys- tems, their design requirements, and their applications.

6.3.4.2 Simplified Theory

The fiber-optic system uses a transmitter at the camera and a receiver at the monitor and the fiber cable in between (Figure 6-15). The following sections describe these three components. By far the most critical is the fiber-optic cable, since it must transmit the video light signal over a long distance without attenuation distortion (changing its shape or attenuation at high frequencies). As shown in Figure 6-15, the signal from the camera is sent to the transmitter via standard coaxial cable. At the receiver end, the output from the receiver is likewise sent via standard wire cable to the monitor or recording system.

The optical transmitter at the camera end converts (modulates) the electrical video analog signal into a corre- sponding optical signal. The output from the transmitter is an optical signal generated by either an LED or an ILD, emitting IR light. When more than one video signal is to be transmitted another option is to transmit multi- ple signals over one fiber using wavelength multiplexing (Section 6.3.4.7).

The multi-fiber-optic cable consists of multiple glass fibers, each acting as a waveguide or conduit for one video optical signal. The glass fibers are enclosed in a pro- tective outer jacket whose construction depends on the application.

The fiber-optic receiver collects the light from the end of the fiber-optic cable and converts (demodulates) the optical signal back into an electrical signal having the same waveform and characteristics as the original video signal at the camera and then sends it to the monitor or recorder.

The only variation in this block diagram for a single camera is the inclusion of a connection, splice, or repeater that may be required if the cable run is very long (many

miles). The connector physically joins the output end of one cable to the input end of another cable. The splice reconnects two fiber ends so as to make them continuous. The repeater amplifies the light signal to provide a good signal at the receiver end.

How does the fiber-optic transmission system differ from the electrical cable systems described in the previous sec- tions? From the block diagram (Figure 6-15) it is appar- ent that two new hardware components are required: a transmitter and a receiver. The transmitter provides an amplitude- or frequency-modulated representation of the video signal at near-IR wavelengths which the fiber optic transmits, and at a level sufficient to produce a high-quality picture at the receiver end. The receiver collects whatever light energy is available at the output of the fiber-optic cable and converts it efficiently, with all the information from the video signal retained, into an electrical signal that is identical in shape and amplitude to the camera output signal. As with any of the transmission means, the fiber- optic cable attenuates the video signal. Figure 6-16 shows the attenuation frequency for current fiber-optic cable as compared with telephone cable, special high-frequency cable, coaxial cable, and early fiber-optic cable.

The fiber-optic cable efficiently transmits the modulated light signal from the camera end over a long distance to the monitor, while maintaining the signal’s shape and amplitude. Characteristics of fiber-optic cable are totally different from those of coaxial cable or two-wire transmis- sion systems.

Before discussing the construction of the fiber-optic cable, we will briefly describe the transmitting light. In any optical material, light travels at a velocity (Vm) characteris- tic of the material, which is lower than the velocity of light (C ) in free space of air (Figure 6-17a).

The ratio (fraction) of the velocity in the material com- pared with that in free space defines the refractive index (n) of the material:

n = C Vm

When light traveling in a medium of a particular refractive index strikes another material of a lower refractive index, the light is bent toward the interface of the two materi- als (Figure 6-17b). If the angle of incidence is increased, a point is reached where the bent light will travel along the interface of the two materials. This is known as the “critical angle” (�C). Light at any angle greater than the critical angle is totally reflected from the interface and follows a zigzag transmission path (Figure 6-17b,c). This zigzag transmission path is exactly what occurs in a fiber- optic cable: the light entering one end of the cable zigzags through the medium and eventually exits at the far end at approximately the same angle. As shown in Figure 6-17c, some incoming light is reflected from the fiber-optic end and never enters the fiber.

Analog Video, Voice, and Control Signal Transmission 165

ATTENUATION (dB/km)

EARLY FIBER OPTIC CABLE: 20 dB/km (1970)

IMPROVED CABLE: 4 dB/km (1972)

CURRENT CABLE: 2– 4 dB/km

0

5

10

15

20

25

30

NOTE: 1 KILOMETER (km) = .67 mile

5 MHz MAX. VIDEO BANDWIDTH

TELEPHONE, UTP 3, 5e CABLE

SPECIAL HIGH FREQUENCY

CABLE

COAXIAL CABLE

(100 TO 1 LOSS)

0.1 1.0 10 100 1000 FREQUENCY (MHz)

FIGURE 6-16 Attenuation vs. frequency for copper and fiber optic cable

In practice, an optical fiber consists of a core, a cladding, and a protective coating. The core material has a higher index of refraction than the cladding material and there- fore the light, as just described, is confined to the core. This core material can be plastic or glass, but glass pro- vides a far superior performance (lower attenuation and greater bandwidth) and therefore is more widespread for long-distance applications.

One parameter often encountered in the literature is the numerical aperture (NA) of a fiber optic, a param- eter that indicates the angle of acceptance of light into a fiber—or simply the ease with which the fiber accepts light. The NA is an important fiber parameter that must be considered when determining the signal-loss budget of a fiber-optic system. To visualize the concept, picture a bottle with a funnel (Figure 6-18). The larger the funnel angle, the easier it is to pour liquid into the bottle. The same concept holds for the fiber. The wider the accep- tance angle, the higher the NA, the larger the amount of light that can be funneled into the fiber from the trans- mitter. The larger or higher an optical fiber NA, the easier it is to launch light into the fiber, which correlates to higher coupling efficiency. Since fiber-optic systems are often coupled to LEDs, which are the light generators at the transmitter, and since LEDs have a less-concentrated,

diffuse output beam than ILDs, fiber optics with high NAs allow more collection of the LED output power.

In order for the light from the transmitter to follow the zigzag path of internally reflected rays, the angles of reflection must exceed the critical angle. These reflection angles are associated with “waveguide modes.” Depending on the size (diameter) of the fiber-optic core, one or more modes are transmitted down the fiber. The characteristics and properties of these different cables carrying single- mode and multimode fibers are discussed in the next section.

Like radio waves, light is electromagnetic energy. The frequencies of light used in fiber-optic video, voice, and data transmission are approximately 3�6 × 1014, which is several orders of magnitude higher than the highest radio waves. Wavelength (the reciprocal of frequency) is a more common way of describing light waves. Visible light with wavelengths from about 400 nm for deep violet to 750 nm for deep red covers only a small portion of the elec- tromagnetic spectrum (see Chapter 3). Fiber-optic video transmission uses the near-IR region, extending from approximately 750 to 1500 nm, since glass fibers propagate light at these wavelengths most efficiently, and efficient detectors (silicon and germanium) are available to detect such light.

166 CCTV Surveillance

CLADDING CORE

LIGHT LOST TO CLADDING

θC = CRITICAL ANGLE

INCOMING LIGHT

SMALL AMOUNT REFLECTED

GLASS

FREE SPACE (AIR)

NA ACCEPTED

NA = SIN θ

REFRACTED LIGHT

θ1

θ1

θ1

θ1

θC

NA = NUMERICAL APERTURE

LIGHT TRANSMITTED THROUGH CABLE CORE

nCORE > nCLADDING

(C)

(B)

(A) REFRACTION OF LIGHT

VELOCITY = VM

VELOCITY = C

θ2

FIGURE 6-17 Light reflection/transmission in fiber optics

6.3.4.3 Cable Types

The most significant part of the fiber-optic signal trans- mission system is the glass fiber itself, a thin strand of very pure glass approximately the diameter of a human hair. The fiber transmits visible and near-IR frequencies with extremely high efficiency. Most fiber-optic system operate at IR wavelengths of 850, 1300, or 1550 nm. Figure 6-19 shows where these near-IR light frequencies are located with respect to the visible light spectrum.

Most short (several miles long) fiber-optic security sys- tems operate at a wavelength of 850 nm rather than 1300 or 1550 nm because 850 nm LED emitters are more read- ily available and less expensive than their 1300 nm or 1550 nm counterparts. Likewise, IR detectors are more sensitive at 850 nm. LED and ILD radiation at the 1300 and 1550 nm wavelengths is transmitted along the fiber- optic cables more efficiently than at the 850 nm frequency; they are used for much longer run cables (hundreds of miles).

Two types of fibers are used in security systems: (1) mul- timode step-index (rarely), and (2) graded-index. These two types are defined by the index of refraction (n) pro- file of the fiber and the cross section of the fiber core.

The two types have different properties and are used in different applications.

6.3.4.3.1 Multimode Step-Index Fiber Figure 6-20a illustrates the physical characteristics of the multimode step-index fiber.

The fiber consists of a center core of index n = 1�47 and outer cladding of index n = 2. Light rays enter the core and are reflected a multiple number of times down the core and exit at the far end. Since this fiber prop- agates many modes, it is called “multimode step-index.” The multimode step-index is usually 50, 100, or even 200 microns (0.002, 0.004, or 0.008 inches) in diameter. The fiber core itself is clad with a thin layer of glass having a sharply different index of refraction. Light travels down the fiber, constantly being reflected back and forth from the interface between the two layers of glass. Light that enters the fiber at a sharp angle is reflected at a sharp angle from the interface and is reflected back and forth many more times, thus traveling more slowly through the fiber than light that enters at a shallow angle. The differ- ence in the arrival time at the end of the fiber limits the bandwidth of the step-index fiber, so that most such fibers provide good signal transmission up to a 20 MHz signal for

Analog Video, Voice, and Control Signal Transmission 167

FIBER CLADDING

NEAR FIELD

FIBER CORE

FAR FIELD

A

C

LIGHT FROM FIBER 1

FIBER 1 FIBER 2

LIGHT FROM FIBER 2

LIGHT ENERGY MISSED BY FIBER

(CROSSHATCH)

NUMERICAL APERTURE: NA = SIN θ = A /C

5.00

SIGNAL LOSS (dB)

NUMERICAL APERTURE MISMATCH RATIO

1.0

0.1

.01

.80 .85 .90 .95 1.00 1.05 1.10

=

NA

TYPICAL NA VALUES IN GLASS

f/#

5.7 2.4511.5 1.5817.5 1.1423.4

0.1 0.2 0.3 0.4 0.5 0.8730.0

NAS NAR

NAR NAS

S = SENDING R = RECEIVING

θ (DEGREES)

θ

FIGURE 6-18 Fiber optic numerical aperture

0

1

2

3

4

5

6

7

8

9

10

400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

850 1300 1550

1600

WAVELENGTH (NANOMETERS)

VIDICON

CCD,CMOS

VISIBLE

NEAR-IR

HUMAN EYE

RELATIVE/ OUTPUT RESPONSE

RESPONSE (RFEFERENCE)

FIGURE 6-19 Fiber optic transmission wavelengths

168 CCTV Surveillance

MULTI-MODE STEP-INDEX FIBER

MULTI-MODE GRADED-INDEX FIBER

@ 850 nm

ATTENUATION: TYPICAL

TYPICAL ATTENUATION:

N1

N2

50 mm

50 mm

N2

(A)

(B)

125 mm DIA.

125 mm DIA.

VARIABLE N

NA = .20

7–15 dB/km @ 850 nm

NA = 0.30

2.5–5.0 dB/km

0.7–2.5 dB/km @ 1300 nm

FIGURE 6-20 Multimode fiber optic cable

about 1 kilometer. This limitation is more than adequate for many video applications.

6.3.4.3.2 Multimode Graded-Index Fiber The multimode graded-index fiber is the workhorse of the video security industry (Figure 6-20b). Its low power attenuation—less than 3 dB (50% loss) per kilometer at 850 nm—makes it well suited for short and long cable runs. Most fibers are available in 50-micron-diameter core with 125-micron total fiber diameter (exclusive of out- side protective sheathing). Graded-index fiber sizes are designated by their core/cladding diameter ratio, thus the 50/125 fiber has 50-micron-diameter core and a 125-micron cladding. The typical graded-index fiber has

a bandwidth of approximately 1000 MHz and is one of the least expensive fiber types available. The 50/125 fiber provides high efficiency when used with a high-quality LED transmitter or for very long distances or very wide bandwidths, with an ILD source. Table 6-3 lists some of the common cable sizes available.

For the graded-index fiber, the index of refraction (n) of the core is highest at the center and gradually decreases as the distance from the center increases (Figure 6-20b). Light in this type of core travels by refraction: the light rays are continually bent toward the center of the fiber-optic axis. In this manner the light rays traveling in the center of the core have a lower velocity due to the high index of refraction, and the rays at the outer limits travel much

FIBER TYPE

DIAMETER *

(MICRONS)

CORE

* FIBER DIAMETER (1 MICRON = .00004 inch)

50/125 50

100/140 100 140

BUFFERING

TYPICAL CABLE PARAMETERS

SINGLE FIBER 2 FIBER

WEIGHT (kg/km)

4 FIBER

250

250

1 mm = 1000 MICRONS

3.4 × 6

3.4

22

22

8

7.1

55

50

2.6

2.6

6.5

250 3.0 6.4

6.5

OD (mm)

OD **

(mm) WEIGHT (kg/km)

OD (mm)

1 kg/km = 0.671 lb/1000 ft

62.5/125 † 62.5 125

† MOST WIDELY USED IN SECURITY APPLICATIONS

** CABLE OUTSIDE DIAMETER OR CROSS SECTION

3.0 × 6.1 18 9.4 65.5

125

CLADDING WEIGHT (kg/km)

Table 6-3 Standard Fiber Optic Cable Sizes

Analog Video, Voice, and Control Signal Transmission 169

faster. This effect causes all the light to traverse the length of the fiber in nearly the same time and greatly reduces the difference in arrival time of light from different modes, thereby increasing the fiber bandwidth–carrying capability. The graded-index fiber satisfies long-haul, wide- bandwidth security system requirements that cannot be met by the multimode step-index fiber.

6.3.4.3.3 Cable Construction and Sizes A fiber-optic cable consists of a single optical fiber that is surrounded by a tube of plastic substantially larger than the fiber itself. Over this tube is a layer of Kevlar reinforcement material. The entire assembly is then cov- ered with an outer jacket, typically made of polyvinyl chlo- ride (PVC). This construction is generally accepted for use indoors or where the cable is easily pulled through a dry conduit. The two approaches to providing primary protection to a fiber is the tight buffer and loose tube (Figure 6-21).

The tight buffer uses a dielectric (insulator) material such as PVC or polyurethane applied tightly to the fiber. For medium- and high-loss fibers (step-index type), such cable-induced attenuation is small compared with over- all attenuation. The tight buffer offers the advantages of smaller bend radii and better crush resistances than loose-

tube cabling. These advantages make tightly buffered fibers useful in applications of short runs where sharp bends are encountered or where cables may be laid under carpeted walking surfaces.

The loose-tube method isolates the fiber from the rest of the cable, allowing the cabling to be twisted, pulled, and otherwise stressed with little effect on the fiber. Micro- bends caused by tight buffers are eliminated by placing the fiber within a hard plastic tube that has an inside diameter several times larger than the diameter of the fiber. Fibers for long-distance applications typically use a loose tube since decoupling of the fiber from the cable allows the cable to be pulled long lengths during installation. The tubes may be filled with jelly to protect against moisture that could condense and freeze and damage the fiber.

Multimode graded-index fiber is available in several pri- mary core sizes: 50/125, 62.5/125, and 100/140. Table 6-3 summarizes the properties of different fiber-cable types used in security systems, indicating the sizes and weights. The first number, in the fiber designation (50 in 50/125), refers to the core outside diameter size, the second (125) to the glass fiber outside diameter (the sizes exclude rein- forcement or sheathing). The fiber size is expressed in microns: 1 micron (�m) equals one one-thousandth of a

TIGHT BUFFER 50/125 FIBER

LOOSE TUBE BUFFER

OUTER PROTECTIVE

JACKET (3 mm DIA.)

TYPICAL OPTICAL CHARACTERISTICS

ATTENUATION: @ 850 nm = 4–6 dB/km @ 1300 nm = 3 dB/km

MINIMUM BANDWIDTH: 200 MHzNOTE: 1000 µm (MICRONS) = 1 mm (MILLIMETER) (125 µm = .125 mm, 50 µm = .05 mm)

STRENGTH MEMBER TIGHT BUFFER

JACKET (940 µm DIA.)

TRANSMITTING CORE (50 µm DIA.)

LOOSE JACKET BUFFER

(250 µm DIA.)

CLADDING (125 µm DIA.)

CORE (50 µm DIA.)

CLADDING (125 µm DIA.)

(3 mm DIA.) JACKET

PROTECTIVE OUTER

PVC OR POLYURETHANE INSULATOR

KEVLAR STRENGTH MEMBER

NUMERICAL APERTURE = NA = .25

FIGURE 6-21 Tight-buffer and loose-tube single fiber optic cable construction

170 CCTV Surveillance

CABLE LOSS TYPE COMMENTS TYPICAL LOSS

(%)

AXIAL-LATERAL DISPLACEMENT (10%)

ANGULAR MISALIGNMENT (2 DEGREES)

END SEPARATION (AIR GAP)

END FINISH:

0.55

0.30

0.32

0.50

0.25

0.17 0.83

1.66

6.7

5.6

31.6

MOST CRITICAL FACTOR

FUNCTION OF NUMERICAL APERTURE

ESSENTIALLY ELIMINATED USING

INDEX MATCHING FLUID

(A)ROUGHNESS (1 MICRON)

(B)NON PERPENDICULAR

CORE SIZE MISMATCH:

±5% DIAMETER TOLERANCE 1% DIAMETER TOLERANCE

NUMERICAL APERTURE (NA) DIFFERENCE OF ± 0.02 (2%) LARGER THAN NAR

CRITICAL FACTOR WHEN NAS IS

INCLUDES FRESNEL LOSS (.35 dB)

NOT COMMONLY FOUND

LOSS OCCURS ONLY WHEN LARGER

CORE COUPLES INTO SMALLER CORE

POWERR

POWERS NOTE: dB = DECIBELS = 10 LOG

S = SENDING FIBER R = RECEIVING FIBER

12.0

7.0

LOSS

(dB)

11.0

4.0 18.0

Table 6-4 Fiber Optic Connector Coupling Losses

millimeter (1/1000 mm). By comparison, the diameter of a human hair is about 0.002 inches or 50 microns.

Each size has advantages for particular applications, and all three are EIA standards. The most popular and least expensive multimode fiber is the 50/125, used exten- sively in video security. It has the lowest NA of any multi- mode fiber, which allows the highest bandwidth. Because 50/125 has been used for many years, established installers are experienced and comfortable working with it. Many connector types are available for terminating the 50/125 cable, an alternative to the 62.5/125 fiber.

The 50/125 and 62.5/125 were developed for tele- phone networks and are now used extensively for video. An 85/125 was developed specifically for computer or digital local networks where short distances are required. The slightly larger 85-micron size permits easier connector specifications and LED source requirements.

The 100/140 multimode fiber was developed in response to computer manufacturers, who wanted an LED- compatible, short-wavelength, optical-fiber data link that could handle higher data rates than coaxial cable. While this fiber was developed for the computer market it is excellent for short-haul CCTV security applications. It is least sensitive to fiber-optic geometry variations and connector tolerances which generally means lower losses at joint connections. This is particularly important in industrial environments

where the cable may be disconnected and connected many times. The only disadvantage of 140 � outside- diameter is that it is nonstandard, so available connectors are fewer and more expensive than those for the 125 � size.

6.3.4.3.4 Indoor and Outdoor Cables Indoor and outdoor fiber-optic cables differ in the jacket surrounding the fiber and the protective sheath that gives it sufficient tensile strength to be pulled through a con- duit or overhead duct or strung on poles. Single indoor cables (Figure 6-22) consist of the clad fiber-optic cable surrounded by a Kevlar reinforcement sheath, wrapped in a polyurethane jacket for protection from abrasion and the environment. The outdoor cable has additional pro- tective sheathing for additional environmental protection.

Plenum fiber-optic cables are available for indoor appli- cations that require specific smoke- and flame-retardant characteristics and do not require the use of a metal conduit. When higher tensile strength is needed, addi- tional strands of Kevlar are added outside the polyethylene jacket and another polyethylene jacket provided over these Kevlar reinforcement elements. Some indoor cables utilize a stranded-steel central-strength member or nonmetallic Kevlar. Kevlar is preferred in installations located in explo- sive areas or areas of high electromagnetic interference, where nonconducting strength members are desirable.

Analog Video, Voice, and Control Signal Transmission 171

(A) INDOOR CABLE

SINGLE

DUPLEX

LOOSE TUBE BUFFERED

OPTICAL FIBER

PVC OUTER JACKET

BRAIDED KEVLAR STRENGTH

MEMBER

(B) OUTDOOR CABLE

KEVLAR REINFORCEMENT

TIGHT BUFFER

OPTICAL FIBER

LOW SMOKE AND FLAME SPREAD FLUOROPOLYMER JACKET

FIGURE 6-22 Indoor and outdoor fiber optic cable construction

The mechanical properties of cables typically found on data sheets include crush resistance, impact resistance, bend radius, and strength.

An outdoor cable or one that will be subjected to heavy stress—in long-cable-run pulls in a conduit or aerial application—uses dual Kevlar/polyethylene layers as just described. The polyethylene coating also retards the dele- terious effects of sunlight and weather.

When two fibers are required, two single cable structures may be paired in siamese fashion (side by side) with a jacket surrounding around them.

If additional fiber-optic runs are required, multi-fiber cables (having four, six, eight, or ten fibers) with sim- ilar properties are used (Figure 6-23). The fibers are enclosed in a single or multiple buffer tube around a tensile-strength member composed of Kevlar and then sur- rounded with an outer jacket of Kevlar.

6.3.4.4 Connectors and Fiber Termination

This section describes fiber-optic connectors, techniques for finishing the fiber ends when terminated with con- nectors, and potential connector problems. For very long cable runs, joining and fusing the actual glass-fiber core and cladding is done by a technique called “splicing.” Splicing joins two lengths of cable by fusing the two fibers (locally melting the glass) and physically joining them in a permanent connection (Section 6.3.4.4.4).

Fiber-optic cables require connectors to couple the opti- cal signal from the transmitter at the camera into the fiber- optic cable, and at the monitoring end to couple the light

output from the fiber into the receiver. If the fiber-optic cable run is very long or must go through various barriers (e.g. walls), the total run is often fabricated from sections of fiber-optic cable and each end joined with connectors. This is equivalent to an inter-line coaxial connector.

A large variety of optical connectors is available for terminating fiber-optic cables. Most are based on butt cou- pling of cut and polished fibers to allow direct transmission of optical power from one fiber core to the other. Such a connection is made using two mating connectors, precisely centering the two fibers into the connector ferrules and fixing them in place with epoxy. The ferrule and fiber sur- faces at the ends of both cables are ground and polished to produce a clean optical surface. The two most common types are the cylindrical and cone ferrule connectors.

6.3.4.4.1 Coupling Efficiency The efficiency of light transfer from the end of one fiber- optic cable to the following cable or device is a function of six different parameters:

1. Fiber-core lateral or axial misalignment 2. Angular core misalignment 3. Fiber end separation 4. Fiber distortion 5. Fiber end finish 6. Fresnel reflections.

Of these loss mechanisms, distortion loss and the effects of fiber end finish can be minimized by using proper techniques when the fibers are prepared for termination.

172 CCTV Surveillance

(A) INDOOR MULTI-FIBER

(C) INDOOR

(B) OUTDOOR AERIAL-SELF SUPPORTING

OPTICAL FIBER

TIGHT BUFFER

CORE TAPE WRAP

LOW SMOKE AND FLAME SPREAD FLUOROPOLYMER JACKET KEVLAR REINFORCEMENT

KEVLAR REINFORCEMENT

CORE TAPE WRAP

TIGHT BUFFER

EPOXY GLASS CENTRAL STRENGTH MEMBER

OUTER POLYETHYLENE JACKET

OPTICAL FIBER

INNER JACKET

FILLING COMPOUND

(D) OUTDOOR (E) ARMORED

FIGURE 6-23 Multi-conductor fiber optic cable

A chipped or scratched fiber end will scatter much of the light signal power, but proper grinding and polishing minimize these effects in epoxy/polish-type connectors.

Lateral misalignment of fiber cores causes the largest amount of light loss, as shown in Figure 6-24a.

An evaluation of the overlap area of laterally misaligned step-index fibers indicates that a total misalignment of 10% of a core diameter yields a loss of greater than 0.5 dB. This means that a fiber core of 0.002 inches (50 microns) must be placed within 0.0001 inches of the center of its connector for a worst-case lateral misalignment loss of 0.5 dB. While this dimension is small, the connection is readily accomplished in the field.

Present connector designs maintain angular alignment well below one degree (Figure 6-24b), which adds only another 0.1 dB (2.3%) of loss for most fibers.

Fiber end–separation loss depends on the NA of the fiber. Since the optical light power emanating from a transmitting fiber is in the form of a cone, the amount of light coupled into the receiving fiber or device will decrease as the fibers are moved apart from each other (Figure 6-24c). A separation distance of 10% of the core diameter using a fiber with an NA of 0.2 can add another 0.1 dB of loss.

Fresnel losses usually add another 0.3 to 0.4 dB when the connection does not use an index-matching fluid (Figure 6-24d).

The summation of all of these different losses often adds up to 0.5–1.0 dB for ST-type (higher for SMA 1906) terminations and connections (Table 6-4).

6.3.4.4.2 Cylindrical and Cone Ferrule Connector In the cylindrical ferrule design, the two connectors are joined and the two ferrules are brought into contact inside precisely guiding cylindrical sleeves. Figure 6-25 shows the geometry of this type of connection.

Lateral offset in cylindrical ferrule connectors is usu- ally the largest loss contributor. In a 50-micron graded- index fiber, 0.5 dB (12%) loss results from a 5-micron offset. A loss of 0.5 dB can also result from a 35-micron gap between the ends of the fibers, or from a 2.5� tilted fiber surface. Commercial connectors of this type reach 0.5–1 dB (12–26%) optical loss for ST type and higher for SMA 1906. Optical-index-matching fluids in the gap further reduce the loss.

The cone ferrule termination technique centers the fiber in one connector and insures concentricity with the mating fiber in the other connector using a cone-shaped

Analog Video, Voice, and Control Signal Transmission 173

LOSS RANGE = 0.3 + 0.2 + 0.1 = 0.6 (GOOD) TO 0.7 + 0.5 + 0.2 + = 1.4 (POOR)

FRESNEL LOSS (FOR PERFECT END FINISH)

LATERAL MISALIGNMENT RATIO L / D END SEPARATION RATIO S/D

MISALIGNMENT ANGLE θ IN DEGREES FIBER FACE ROUGHNESS (µm)

TOTAL CONNECTOR LOSS = D + S + 0 + E (dB)

LATERAL MISALIGNMENT LOSS (dB)

ANGULAR TILT

LOSS

END SEPARATION LOSS (dB)

SURFACE ROUGHNESS LOSS (dB)(dB)

4

3

2

1

.1 .2 .3 .4 .5 .1 .2 .3 .4 .5

1

2

3 .5 NA

.2 NA

.15 NA

.15 NA

.2 NA

.5 NA

.5

1.0

0 1 8 15

D

D

S L

D

1.0

.5

1.5

1 2 3 4 5

(A) AXIAL (LATERAL) DISPLACEMENT (D ) (C) END SEPARATION (S )

(B) ANGULAR MISALIGNMENT θ (D) END FINISH

θ

FIGURE 6-24 Factors affecting fiber optic coupling efficiency

CYLINDRICAL CONICAL

SLEEVE PLUG PLUG

SLEEVE

FIBER FIBER

FIGURE 6-25 Cylindrical and conical butt-coupled fiber optic ferrule connectors

plug instead of a cylindrical ferrule. The key to the cone connector design is the placement of the fiber-centering hole (in the cone) in relationship to the true center, which exists when the connector is mated to its other half. A fiber (within acceptable tolerances) is inserted into the ferrule, adhesive is added, and the ferrule is compressed to fit the fiber size while the adhesive sets. The fiber faces and

ferrule are polished to an optical finish and the ferrule (with fiber) is placed into the final alignment housing. Most low-loss fiber-optic connections are made utilizing the cone-shaped plug technique. The two most popular cone-shaped designs are the small-fiber resilient (SFR) bonded connector and the SMA, a redesigned coaxial con- nector style (Figure 6-26).

174 CCTV Surveillance

TYPE: SMA THREADED—SCREW ON

TYPE: ST, SFR (SMALL FIBER RESILIENT) POLARIZED AND SPRING LOADED QUARTER

TURN BAYONET LOCK

FIGURE 6-26 SMA and SFR connectors

Both use the cone-shaped ferrule, which provides a reli- able, low-cost, easily assembled termination in the field. Both connectors can terminate fibers with diameters of 125-micron cladding.

The technique eliminates almost all fiber and connector error tolerance buildup that normally causes light losses. It makes use of a resilient material for the ferrule, metal for the construction of the retainer assembly, and a rugged metallic connector for termination. The fiber alignment is repeatable after many “connects” and “disconnects” due to the tight interference fit of the cone-shaped ferrule into the cone-shaped mating half. This cone design also forms a sealed interface for a fiber-to-fiber or fiber-to-active-device junction, such as fiber cable to transmitter or fiber cable to receiver. Tolerances in the fiber diameter are absorbed by the resiliency of the plastic ferrule. This connector offers a maximum signal loss of 1.0 dB (26%) and provides repeatable coupling and uncoupling with little increase in light loss.

The popular SMA-style connector is compatible with many other SMA-manufacturer-type connectors and termi- nates the 125-micron fibers. Internal ferrules insure axial fiber alignment to within 0.1�. The SMA connector has a corrosion-resistant metal body and is available in an envi- ronmentally sealed version.

6.3.4.4.3 Fiber Termination Kits An efficient fiber-optic-cable transmission system relies on a high-quality termination of the cable core and cladding. This step requires the use of perhaps unfa- miliar but easy techniques with which the installer must be acquainted. Fiber-terminating kits are available from most fiber-cable, connector, and accessory manufacturers. Figure 6-27 shows a complete kit, including all grind- ing and polishing compounds, alignment jigs, tools, and instructions.

Manufacturers can provide descriptions of the vari- ous techniques for terminating the ends of fiber-optic cables, including cable preparation, grinding, polishing, testing, etc.

6.3.4.4.4 Splicing Fibers Splicing of multimode fibers is sometimes necessary in systems having long fiber-optic-cable runs (longer than 2 km). In these applications it is advantageous to splice cable sections together rather than connect them by using connectors. A splice made between two fiber-optic cables can provide a connection with only one-tenth the optical loss of that obtained when a connector is inserted between fibers. Good fusion splices made with an electric arc pro- duce losses as low as 0.05–0.1 dB (1.2–2.3% loss). Making a splice via a fusing technique is more difficult and requires more equipment and skill than terminating the end of a fiber with a connector. It is worth the effort if it elimi- nates the use of an in-line amplifier. The splice can also be used to repair a damaged cable, eliminating the need to add connector terminations that would decrease the light signal level.

6.3.4.5 Fiber-Optic Transmitter

The fiber-optic transmitter is the electro-optic transducer between the camera video electrical signal output and the light signal input to the fiber-optic cable (Figure 6-15). The function of the transmitter is to efficiently and accu- rately convert the electrical video signal into an optical signal and couple it into the fiber optic. The transmitter electronics convert the amplitude-modulated video signal through LED or ILD into an AM or FM light signal, which faithfully represents the video signal. The transmitter con- sists of an LED for normal security applications or an ILD when a long range transmission is required. The former is used for most CCTV security applications. Figure 6-28 illustrates the block diagram for the transmitter unit.

6.3.4.5.1 Generic Types The LED light source is a semiconductor device made of gallium arsenide (GaAs) or a related semiconductor compound which converts an electrical video signal to an optical signal. The LED is a diode junction that sponta- neously emits nearly monochromatic (single wavelength or color) radiation into a narrow light beam when current is passed through it. While the ILD has a very narrow beam

Analog Video, Voice, and Control Signal Transmission 175

FIBER END GRINDING AND POLISHING CABLE TERMINATING KIT

WET WITH WATER

SMA POLISH TOOL

600 GRIT

3 MICRON

0.3 MICRON

GRIND AND POLISH IN FIGURE 8 PATTERN

FIGURE 6-27 Fiber optic termination kit

SCENE

CAMERA

COAX

IMPEDANCE MATCHING

INPUT ATTENUATOR

STAGE

LINEARIZING MODULATOR

STAGE

HIGH LINEARITY

DRIVER AMPLIFIER

LIGHT EMITTING DIODE (LED) WITH OPTICS

LOW LOSS CONNECTOR

FIBER OPTICS

FIBER OPTIC TRANSMITTER

CABLE

LENS

FIGURE 6-28 Block diagram of LED fiber optic transmitter

width and is more powerful, the LED is more reliable, less expensive, and easier to use. The ILD is used in very long distance, wide-bandwidth fiber-optic applications.

The LED’s main requirements as a light source are: (1) to have a fast operating speed to meet the bandwidth requirements of the video signal, (2) to provide enough optical power to provide the receiver with a signal-to-noise (S/N) ratio suitable for a good television picture, and (3) to produce a wavelength that takes advantage of the low-loss propagation characteristics of the fiber.

The parameters that constitute a good light source for injecting light into a fiber-optic cable are those that produce as intense a light output into as small a cone

diameter as possible. Another factor affecting the light- transmission efficiency is the cone angle of the LED out- put that can be accepted by and launched down the fiber-optic cable. Figure 6-29 illustrates the LED-coupling problem.

The entire output beam from the LED (illustrated by the cone of light) is not intercepted or collected by the fiber-optic core. This unintercepted illumination loss can be a problem when the light-emitting surface is separated from the end of the fiber core. Most LEDs have a lens at the surface of the LED package to collect the light from the emitting source and concentrate it onto the core of the fiber.

176 CCTV Surveillance

LIGHT EMITTING DIODE (LED) JUNCTION

LED OUTPUT BEAM

LENS AND

LED

WINDOW

FIBER OPTIC

CORE

CLADDING

LIGHT BEAM

LENS

FIGURE 6-29 LED light beam output cone angle

6.3.4.5.2 Modulation Techniques For video security applications, the electrical signal from the camera is AM or FM and converted to light output variations in the LED or ILD. The optical output power varies directly to the electrical input signal for AM and is constant for FM. LEDs with an 850 nm IR wavelength emission are best suited since they can be amplitude mod- ulated: the electrical video signal can be converted to a light output signal that is a near-linear function of the LED drive current. This produces a very faithful transformation of the electrical video information to the light information that is transmitted along the fiber-optic cable.

6.3.4.5.3 Operational Wavelengths An important characteristic of the transmitter output is the wavelength of the emitted light. This should be compatible with the fiber’s minimum-attenuation wavelength, which is 850 nm (in the IR region) for most CCTV fiber-optic cable. The wavelength of light emitted by an LED depends on the semiconductor material composition. Pure GaAs diodes emit maximum power at a wavelength of 940 nm (near- IR), which is undesirable because most glass fibers have a high attenuation at that wavelength. Adding aluminum to GaAs to produce a GaAlAs diode yields a maximum power output at a wavelength between 800 and 900 nm, with the exact wavelength determined by the percentage

of aluminum. In most transmitters today, the emitting wavelength is 850 nm, which matches the maximum trans- mission capability of the glass fiber.

Alternative transmitting wavelengths are 1060, 1300, and 1550 nm, which are regions where glass fibers exhibit a lower attenuation and dispersion than at 850 nm. These wavelengths are produced by combining the element indium with gallium arsenide (to get InGaAs) and are used in some long-distance transmission applications.

6.3.4.6 Fiber-Optic Receiver

The term receiver at the output end of the fiber-optic cable refers to a light-detecting transducer and its related electronics that provides any necessary signal condition- ing to restore the signal to its original shape at the input and additional signal amplification. The most common fiber-optic receiver uses a photodiode to convert the inci- dent light from the fiber into electrical energy. To inter- face the receiver with the optical fiber, the proper match between light source, fiber-optic cable, and light detector is required. In the AM transmission system, the optical power input at the fiber is modulated so the photodetector operating in the photocurrent mode must provide good linearity, speed, and stability. The photodiode produces

Analog Video, Voice, and Control Signal Transmission 177

FIBER OPTIC

RECEIVER OPTICS

OPTICAL DETECTOR (PIN DIODE)

HIGH GAIN

VIDEO AMPLIFIER

VARIABLE GAIN POST

AMPLIFIER

OUTPUT DRIVER

MONITOR

GAIN

FIBER OPTIC CONNECTOR

COAXIAL CABLE

VIDEO OUTPUT

FIBER OPTIC RECEIVER

SIGNAL

FIGURE 6-30 Fiber optic receiver block diagram

no electrical gain and is therefore followed by circuits that amplify electrical voltage and power to drive the coaxial cable. Figure 6-30 illustrates the block diagram for the receiver unit.

The light exiting from the receiver end of an optical fiber spreads out with a divergence approximately equal to the acceptance cone angle at the transmitter end of the fiber. Photodiodes are packaged with lenses on their housings so that the lens collects this output energy and focuses it down onto the photodiode-sensitive area.

After the light energy is converted into an electrical signal by the photodiode, it is linearly amplified and condi- tioned to be suitable for transmission over standard coaxial cable or two-wire UTP to a monitor or recorder.

6.3.4.6.1 Demodulation Techniques The receiver demodulates the video light signal to its original base-band video form. This takes the form of either AM or FM demodulation. Since FM modulation– demodulation is less sensitive to external electrical influ- ences it is the technique of choice in most systems.

6.3.4.7 Multi-Signal, Single-Fiber Transmission

The primary attribute of fiber-optic transmission is the cable’s wide signal bandwidth capability. Transmitting a single video signal on a single fiber easily fits within the bandwidth capability of all fiber-optic cables. Mod- ulators and demodulators in transmitters, receivers, and transceivers permit transmission of bidirectional video, audio, and control signals over a single optical-fiber cable. Using the full-duplex capabilities of the system, the transceiver at the camera transmits video and audio signals

from the camera location to the monitor location while simultaneously receiving audio, control, or camera gen- lock signals from the transceiver at the monitor location. All transmissions occur via the same single optical-fiber cable. The transmitter and receiver contain all circuitry for the bidirectional transmission of pan/tilt, zoom, focus, iris, contact-closure, and video in the opposite direction.

When more than one video signal is to be transmitted by optical fiber between two points, either multiple fibers may be used or the signals may be combined using wavelength division multiplexing (WDM MUX), thus saving the cost of additional fibers and expensive multi-fiber connectors. Using this technique the outputs from each optical trans- mitter operating at different wavelengths (1060, 1300, and 1550 �m) are modulated by separate video signals and combined on a single optical fiber and combined using WDM MUX. These video signals may then be separated at the other end of the fiber by a WDM de-multiplexer (WDM DE-MUX) (Figure 6-31).

Typically two or more wavelengths are provided by two LED transmitters operating at wavelengths between 850 and 1550 nm. The WDM MUX and DE-MUX may be fabri- cated using an optical coupler and splitter assembly, using lens and grating components. The lens focuses each of the channels onto the grating, which then separates the chan- nels according to wavelength and according to the grating spacing. Data sheets for a typical WDM MUX/DE-MUX devices include the following specifications:

1. Number of Channels: The number of video signals that can be multiplexed and de-multiplexed over the optical fiber to which the WDM MUX/DEMUX are connected.

178 CCTV Surveillance

FF631

WAVELENGTH DIVISION MULTIPLEXING (WDM)-TRANSMITTER

DWDM-RECEIVER

1060 nm

1300 nm

1550 nm

LASER/LED MODULATED

SINGLE FIBER OPTIC

LIGHT COUPLER

COLLIMATED

ELECTRICAL SIGNAL TO LIGHT PULSE

MODULATORS

GRATING **

BEAM

* UP TO 32 CHANNELS OF VIDEO, VOICE, DATA

VIDEO 2

INPUT: * VIDEO 1

VIDEO 3

LIGHT TO ELECTRICAL SIGNAL DEMODULATORS

LIGHT DETECTORS

** GRATING FUNCTION: DISPERSE MULTI-WAVELENGTH LIGHT INTO CONSTITUANT COMPONENTS (λ1 λ 2 λ 3 …) OUTPUT:

VIDEO 1

VIDEO 2

VIDEO 3

λ 1 λ 2 λ 3

FIGURE 6-31 Wavelength division multiplexing and de-multiplexing video signal

2. Center Wavelengths: Center wavelength of the channels over which the video signals are multiplexed.

3. Channel Spacing: The minimum distance (wave- length or frequency) between channels in a WDM MUX/DEMUX system. In the illustration the chan- nel spacing is approximately 0.8 nm, approximately 100 GHz.

4. Bandwidth (also referred to as Passband Width): The line- width of a specific wavelength channel. A manufacturer generally specifies the line-width at 1 dB, 3 dB and 20 dB insertion loss as shown in Figure 6-32.

5. Maximum Insertion Loss: Loss sustained by the video sig- nals when the WDM MUX/DE-MUX is applied in a system. Typical values range from 1.5 dB for a 4-channel device to 6 dB for a high number of channels, WDM MUX/DE-MUX.

6. Isolation: The loss or attenuation between video signal channels, usually more than 30 dB.

Figure 6-33 illustrates two typical channels over which the video signals 1540.56 �m and 1541�35 �m are multiplexed.

6.3.4.8 Fiber Optic—Advantages/Disadvantages

Why go through all the complexity and extra expense of converting the electrical video signal to a light signal and then back again? Fiber optics offers several very important features that no electrical cabling system offers, including:

• ultra-wide bandwidth supporting multiple video, audio, control, and communications signals on one fiber

• complete electrical isolation • complete noise immunity to RFI, EMI, and electromag-

netic pulse (EMP) • transmission security (fiber-optic cable is hard to tap) • no spark or fire hazard or short-circuit possibility • absence of crosstalk • no RFI/EMI radiation. Table 6-5 compares the features of coaxial and fiber-optic transmission.

6.3.4.8.1 Pro Widest Bandwidth. In general the bandwidth capacity is directly proportional to the carrier frequency. Light

Analog Video, Voice, and Control Signal Transmission 179

NOITRESNI )Bd( SSOL 0

–5

–10

–15

–20

–25

–30

)mn( HTGNELEVAW

1542.0 1542.5 1543.0 1543.5 1544.0 1544.5 1545.0 1545.5

–35

–40

LENNAHC GNICAPS

INSERTION LOSS

SSAP DNAB

PALREVO LANGIS KLATSSORC—NOIGER

FIGURE 6-32 Line-width vs. insertion loss of a specific wavelength channel

(and near IR) frequencies are approximately 1014 Hz. Typ- ical video microwave transmitters operate at 1010 GHz or 1010 Hz. Fiber optics has a 104 or 10,000 times higher bandwidth capability than microwave.

Electrical Isolation. The complete electrical isolation of the transmitting section (i.e. the camera, lens controller, pan/tilt, and related equipment) from the receiving section (i.e. the monitor, recorder, printer, switching net- work, and so on) is very important for inter-building and intra-building locations when a different electrical power source is used for each location. Using fiber-optic transmis- sion prevents all possibility of ground loops and ground voltage differences that could require the redesign of a coaxial cable–based system.

RFI, EMI, and EMP Immunity. When a transmission path runs through a building or outdoors past other electrical equipment, the site survey usually cannot uncover all pos- sible contingencies of existing RFI/EMI noise. This is also true of EMP and lightning strikes. Therefore, using fiber optics in the initial design prevents any problems caused by such noise sources.

Transmission Security. Since the fiber optic has no electrical noise to leak and no visible light, it exhibits excellent inherent transmission security and it is hard to intercept. Methods for compromising the fiber-optic cable

are difficult, and the intrusion is usually detected. To tap a fiber-optic cable, the bare fiber in the cable must be iso- lated from its sheath without breaking it. This will probably end the tapping attempt. If the bare fiber is successfully isolated, an optical tap must be made, the simplest of which is achieved by bending the fiber into a small radius and extracting some of the light. If a measurable amount of power is tapped (which is necessary for a useful tap), the tap can be detected by monitoring the power at the system receiver. In contrast, tapping a coaxial cable is easy to do and hard to detect.

No Fire Hazards. Since no electricity is involved in any part of the fiber-optic cable, there is no chance or oppor- tunity for sparks or electrical short circuits, and hence no fire hazards. Short circuits and other hazards encoun- tered in electrical wiring systems can start fires or cause explosions. When a light-carrying fiber is severed, there is no spark, and a fiber cannot short-circuit in the electrical meaning of the term.

Absence of Crosstalk. Because the transmission medium is light, there is no crosstalk between any of the fiber-optic cables. Therefore there is no degradation due to the close proximity of cables in the same bundle, as there can be when multiple channels are encased in the same electrical cable.

180 C

C T

V S

u rveillan

ce

PAN / TILT CONTROLLER

VIDEO

DOME

PAN/ TILT/ZOOM PLATFORM

TRANSMITTER

4 CHANNEL *

MUX /DMUX

4-CHANNEL *

MUX / DMUX

* MANY WDM/DMDM ARE BI-DIRECTIONAL

BI-DIRECTIONAL WAVELENGTH DIVISION MULTIPLEXING (WDM)

TRANSMITTER

RECEIVER

TRANSMITTER

CAMERA 1

CAMERA 2

CAMERA 3

VIDEO

VIDEO

PAN/ TILT CAMERA

LENS CONTROLS

SINGLE FIBER OPTIC IN 1550 nm BAND

SWITCHER

RECEIVER

TRANSMITTER

RECEIVER

RECEIVER

LENS CONTROLLER

DISPLAY

λ 1

λ 2

λ 3

λ 4 λ 1

λ 2

λ 3

λ4

FIGURE 6-33 Video signals and controls multiplexed over four channels

Analog Video, Voice, and Control Signal Transmission 181

dB/100 ft dB/1000 ft dB/km

RG59

RG6

RG11

DESIGNATION CABLE TYPE

COAXIAL

COAXIAL

COAXIAL

10/125 *

50/125

140/200

MINI–COAX

MINI–COAX

2546 †

RG179B/U

RG59 MINI

2422/UL1384

— — — —

—

1 KILOMETER (km) = 3280 FEET (ft) 1 MILE (Mi) = 1.609 KILOMETERS (km) 1 POUND (lb) = .454 KILOGRAMS (kg)

850 NM **

1300 NM FIBER OPTIC

OPTIC FIBER

1300 NM 850 NM

850 NM 1300 NM

FIBER OPTIC

3–6.0

2.5–6.0

.8–4.5

.50 –1.0 4–7.0

.4–.8

ATTENUATION @ 5–10 MHz DIAMETER OUTSIDE

(inches)

COAXIAL

MINI–COAX

.01–.02

.12–.21

.09–.18

.08–.18

.02–.14

.1–.2

1.2–2.1

.9–1.8

.8–1.8

.2–1.4

WEIGHT (lb) PER 100 ft

3.5–4.0

1.5

7.9

9 –11

0.9

1.4

1.0

* USED ONLY IN VERY LONG DISTANCE, WIDE BANDWIDTH APPLICATIONS

** TRANSMISSION WAVELENGTH

(NANOMETER–NM) † MOGAMI

2895 † MINI–COAX

1.0

1.3

.8

.51

1.82

2.0

3.96

2.1

10.0

13.0

8.0

5.1

18.2

20.0

39.6

21.0

32.8

42.6

26.2

16.7

59.7

65.6

129.9

69.0

.242

.135

.272

.405

.13

.079

.089

.12

.244

.036

.118 1.0

Table 6-5 Comparison of Fiber Optic and Coaxial Cable Transmission

No RFI or EMI Radiation. Fibers do not radiate energy. They generate no interference to other systems. There- fore, the fiber-optic cable will not emit any measurable EMI/RFI radiation, and other cabling in the vicinity will suffer no noise degradation. There are no FCC require- ments for fiber-optic transmission.

6.3.4.8.2 Con Higher Cost. Coaxial cable and connectors are inexpen- sive and no transmitter/receiver pairs are required. For short distances if new cable must be run, coaxial is the most cost-effective.

Connector Termination More Difficult. Fiber-optic cable and connectors cost more than coaxial. Terminating fiber cables takes longer than coaxial cables and requires more technical skill.

6.3.4.9 Fiber-Optic Transmission: Checklist

The following are some questions that should be asked when considering the use or design of a new fiber-optic transmission system.

1. What are the lengths of cable runs? If over 500 feet, then fiber optic should be considered. In screen rooms or tempest areas, runs as short as 10 feet sometimes require fiber-optic cable.

2. What size core/clad-diameter fiber should be used? The most common diameter is 50/125 microns.

3. What wavelength should be used—850, 1060, 1300, or 1550 nm? The most common wavelengths are 850 and 1300 nm.

4. How many fibers are necessary for transmitting video, audio, and controls? Should single- or multi-fiber cable be used?

5. Are the cable runs going to be indoors or outdoors? Separate the indoor and outdoor requirements and determine if outdoor fiber cables are required. What will the outdoor environment be (lighting, etc.)?

6. If outdoors, will the fiber be strung on poles, surface- mounted on the ground, undergo direct burial, or pass through a conduit? Choose cable according to manufacturers’ recommendations.

7. If indoors, will it be in a conduit, cable tray or trough, plenum, or ceiling? Choose cable according to manu- facturers’ recommendations.

8. What temperature range will the fiber-optic cable experience? Most cable types will be suitable for most indoor environments. For outdoor use, the cable cho- sen must operate over the full range of hot and cold temperatures expected and must withstand ice and wind loading if mounted above ground level.

9. Are there any special considerations such as water, ice, chemicals? See manufacturers’ specifications for extreme environmental hazards.

10. Are there special safety codes? Fiber-optic cable is avail- able with plenum-grade or special abrasion-resistant construction.

182 CCTV Surveillance

11. Should spare cables be included? Each design is dif- ferent, but it is prudent to include one or more spare fiber-optic cables to account for cable failure or future system growth. The number of spares also depends on how easy or difficult it is to replace a cable or add to existing cables.

6.4 WIRED CONTROL SIGNAL TRANSMISSION

Fixed cameras do not require any control functions. Mov- ing cameras require pan, tilt, focus and sometimes iris control signals for proper operation.

6.4.1 Camera/Lens Functions

Lenses can require zoom, focus, and iris-control signals.

6.4.2 Pan/Tilt Functions

Moving cameras require pan/tilt functions to scan the camera horizontally, tilt it vertically, and set preset point- ing directions to specific locations in the scene.

6.4.3 Control Protocols

The simplest controls can take the form of on/off or pro- portional voltage control wiring for each function. These direct controls require the largest number of wires. The most standard two- and four-wire control protocol for cameras, lens, and pan/tilt platforms are the RS422 and RS485.

6.5 WIRELESS VIDEO TRANSMISSION

Most video security systems transmit video, audio, and con- trol signals via coaxial cable, two-wire, or fiber-optic trans- mission means. These techniques are cost-effective and reliable, and provide an excellent solution for transmis- sion. However, there are applications and circumstances that require wireless transmission of video and other signals.

The video signal can be transmitted from the camera to the monitor through the atmosphere, without having to connect the two with hard wire or fiber. The most famil- iar technique is the transmission of commercial television signals from some distant transmitter tower to consumer television sets, broadcast through the atmosphere on VHF and UHF radio frequency channels.

Commercial broadcasting is of course rigidly controlled by the FCC, whose regulations dictate its precise usage.

Microwave transmission also is controlled by the FCC. Rules are set forth and licenses are required for cer- tain frequencies and applications, which limits usage to specific purposes. The US government currently exer- cises strict control over transmission of wireless video via RF and microwave. Up until recently, RF and microwave atmospheric video transmission links were limited to gov- ernmental agencies (federal, state, and local) that could obtain the necessary licenses. Now some low-power RF and microwave transmitters and receivers suitable for short links (less than a mile) are available for use without an FCC license. High power and RF microwave links are licensable by private users after a frequency check is made with the FCC.

6.5.1 Transmission Types

Some examples of wireless TV transmission described in the following sections include microwave (ground- to-ground station, satellite), RF over VHF or UHF, and light-wave transmission using IR beams. The hardware cost of RF, microwave, and lightwave systems is consid- erably higher than any of the copper-wire or fiber-optic systems, and such systems should be used only when abso- lutely necessary as when their use avoids expensive cable installations (such as across roadways), or in temporary or covert applications, wireless transmission becomes cost-effective.

The results obtainable with hard-wired copper-wire or fiber-optic video transmission are usually predictable, with the exception of interference that might occur due to the copper-wire cables running near electromagnetic radiating equipment or electrical storms. The results obtained with wireless transmission are generally not as predictable because of the variable nature of the atmo- spheric path and materials through which RF, microwave, or light signals must travel, as well as the specific trans- mitting and propagating characteristics of the particu- lar wavelength or frequency of transmission. Each of the three wireless transmitting regimes acts differently because of the wide diversity in frequencies at which they transmit.

6.5.2 Frequency and Transmission Path Considerations

The RF link constitutes the lowest carrier frequency (Figure 6-34). It penetrates many visually opaque materials, goes around corners, and does not require a line-of-sight path (i.e. a receiver in sight of the transmit- ter) when transmitting from one location to another. The radio frequencies are, however, susceptible to attenuation and reflection by metallic objects, ground terrain, or large

Analog Video, Voice, and Control Signal Transmission 183

POWER OUTPUT

100

0 100 MHz 500200 1000 MHz

1 GHz 2 GHz

FREQUENCY

10 GHz 20 GHz

MICROWAVE SPECTRUM

RF SPECTRUM

VHF UHF

150 980

920–930 MHz

2.4–2.5 GHz

8 13 GHz

10.525 GHz

21–24 GHz

5 GHz

5–5.8 GHz

FIGURE 6-34 Wireless video transmission frequencies

buildings or structures, and therefore they sometimes pro- duce unpredictable results.

The microwave link requires an unobstructed line of sight; any metallic or wet objects in the transmission path cause severe attenuation and reflection, often rendering a system useless. However, metallic poles or flat surfaces can sometimes be used to reflect the microwave energy, allow- ing the beam to turn a corner. Reflection of this type does reduce the energy reaching the receiver and the effective range of the system. Some microwave frequencies pene- trate dry nonmetallic structures such as wood or drywall walls and floors, so that non-line-of-sight transmission is possible.

The frequency range most severely attenuated by the atmosphere and blocked completely by any opaque object is a light-wave signal in the near-IR region. The IR beam can be strongly attenuated by heavy fog or precipita- tion, severely reducing its effective range as compared with clear-line-of-sight, clear-weather conditions. As would be expected, the IR-wavelength system requires a clear line of sight with no opaque obstructions whatsoever between the transmitter and the receiver. The IR beam can be reflected off one or more mirrors to go around corners. The advantages of the IR system over RF and microwave links are: (1) security (since it is hard to tap a narrow light beam), (2) high bandwidth (able to carry multiple channels of information), and (3) bidirectional operation.

6.5.3 Microwave Transmission

Microwave systems applicable in television transmission have been allocated frequencies in bands from 1 to 75 GHz (see Table 6-6).

Microwave frequencies, which approach light-wave fre- quencies, are usually transmitted and received by parabol- ically shaped reflector antennas or metallic horns. Even when a line of sight exists, there can be signal fading, caused primarily by changes in atmospheric conditions between the transmitter and the receiver, a problem that must be taken into account in the design. This fading can result at any frequency, but in general is more severe at the higher microwave frequencies.

6.5.3.1 Terrestrial Equipment

For terrestrial use, several manufacturers provide reliable microwave transmission equipment suitable for transmit- ting video, audio, and control signals over distances of from several hundred feet to 10–20 miles in line-of-sight conditions.

One system transmits a single NTSC video channel and two 20 kHz audio channels over a distance of 1 mile. A high-gain directional antenna is available to extend the system operating range to several miles. Figure 6-35a shows the transmitter and receiver units. This system operates at

184 CCTV Surveillance

BAND/USE * FREQUENCY BAND (GHz)

S

G

C

J

H

M

P

N

K

R

1.2–1.7

2.6–3.95

3.95–5.85

4.9–7.05

5.85–8.2

7.05–10.0

10.0–15.0

12.4–18.0

15.0–22.0

18.0–26.5

26.5–40.0

1 GIGAHERTZ (GHz) = 1000 MHz

2.45

8.4–8.6

10.4–10.6

10.525

10.35–10.8

21.2–23.2

24.125

X 8.2–12.4

VIDEO, AUDIO, INTRUSION

VIDEO UP TO 3 Mi RANGE

VIDEO, VOICE, INTRUSION

VIDEO TRANSMITTER

VIDEO TRANSMITTER

CONSUMER MICROWAVE OVEN

2.4–2.5

USAGE RESTRICTIONS

L GOVERNMENT SECURITY

LAW ENFORCEMENT ONLY

LOW POWER—NO RESTRICTIONS NO FCC LICENSE REQUIRED

5–5.8 VIDEO TRANSMITTER

VIDEO TRANSMITTER

LOW POWER—NO RESTRICTIONS NO FCC LICENSE REQUIRED

S

VIDEO TRANSMITTER

LOW POWER /HIGH POWER

FCC PART 15

* ALSO SEE TABLE 6-7 FCC PART 15.249 TRANSMITTER, ANY TYPE OF MODULATION

902–928 MHz–50 mV/M MAXIMUM AT 3 METERS 2.4–2.F835 GHz–50 mV/M MAXIMUM AT 3 METERS 5.735–5.875 GHz–250 mV/M MAXIMUM AT 3 METERS

FCC PART 15.247 TRANSMITTER USING SPREAD SPECTRUM 902–928 MHz–1 WATT MAXIMUM 2.4000–2.4835–1 WATT MAXIMUM 5.725–5.675 GHz–1 WATT MAXIMUM

C

V

HIGH POWER—LICENSE REQURIED

SECURITY FREQUENCY

RANGE (GHz)

HIGH POWER—LICENSE REQURIED

1.2–1.7

5–5.8 LOW POWER/HIGH POWER

FCC PART 15

2.4–2.5

—

—

—

—

—40–75

Table 6-6 Microwave Video Transmission Frequencies

a carrier frequency of 2450–2483.5 MHz with a power out- put of 1 watt. The transmitter and receiver operate from 11 to 16 volts DC derived from batteries, an AC-to-DC power supply, or 12 volts DC vehicle power. The microwave trans- mitter utilizes an omnidirectional antenna. A high-gain, low-noise receiver collects the microwave transmitter sig- nal with an omnidirectional or directional antenna. The system has a selectable video bandwidth from 4.2 MHz for enhanced sensitivity or 8 MHz for high resolution and has a single or dual audio sub-carrier channel for audio communications between the two sites. It transmits monochrome or color video with excellent quality.

The 2450–2483.5 MHz band is available for a variety of industrial applications and requires an FCC license for operation. The system operates indoors or outdoors, uses FM, and provides immunity from vehicles, power lines, and other AM-type noise sources. The microwave frequency utilized has the ability to penetrate dry walls and ceilings and reflect off metal surfaces.

Figures 6-35b, c show examples of small short-range microwave transmitters operating at 2.4 GHz and 5.8 GHz

designed for outdoor use. These systems use directional patch antennas pointed toward each other to provide the necessary signal at the receiver from the transmitter.

The systems are weatherproof, pedestal mounted, and designed for permanent installation. They transmit excellent full-color or monochrome pictures over an FM carrier in a frequency range of 2.4 GHz and 5.8 GHz with a video bandwidth of 10 MHz. In addition to the video channel, the system is capable of providing up to three voice or data (control) channels. The data channels may be used to control pan/tilt, zoom, focus, and iris at the camera location. Low power systems do not require FCC licensing. FCC licensing is required for high power systems and can be obtained for government and industrial users, providing an authorized interference survey is made to verify that no interference will result in other equipment.

Other variations and functions, the microwave transmit- ter/receiver systems can perform include:

1. Operation in any frequency band from 8.5 to 12.4 GHz with output powers up to 100 milliwatts.

Analog Video, Voice, and Control Signal Transmission 185

(A) 2.4 GHz TRANSMITTER/RECEIVER

(B) 2.4 GHz OUTDOOR (C) LONG RANGE 5.8 GHz

FIGURE 6-35 Monochrome/color microwave video transmission systems

2. Operation as a command-and-control unit providing a multi-channel system for transmitting control sig- nal information. The commands are encoded at the transmitter and decoded at the receiver to control power on/off, lens focus, zoom and iris, and camera motion (pan/tilt).

3. An audio channel to provide simplex (one-way) or duplex (two-way) communications (IR system).

4. The ability to sequence through and transmit the video outputs from multiple surveillance cameras. The receiver and control units are located at the monitor site and the transmitter and sequencer units are located with the CCTV cameras. The camera outputs are fed to the sequencer unit. The operator at the receiver end controls the sequencing of the eight cameras and has the option to: (1) manually advance through the

186 CCTV Surveillance

cameras, (2) have the cameras sequence automatically, or (3) change the camera dwell time.

6.5.3.2 Satellite Equipment

Microwave transmission of video signals can be accom- plished via satellite. Such systems are in extensive use for earth-to-satellite-to-earth communications, in which one ground-based antenna transmits to an orbiting syn- chronous satellite repeater, which relays the microwave signal at a shifted frequency to one or more receivers on earth (Figure 6-36).

While this type of communication and transmission for video security applications was not put into widespread use for analog video systems, it now is enjoying wide spe- cial use for digital video Internet (WWW) systems. The satellites used for transmission are in a synchronous orbit at an altitude of 22,300 miles and appear stationary with respect to the earth. Satellites are placed in a synchronous or stationary orbit to permit communications from any two points in the continental USA by a single “up” and a single “down” transmission link. Consequently, a characteristic of domestic satellite video communications is that the trans-

mission cost is independent of terrestrial distance. It takes 0.15 seconds for a microwave signal traveling at the speed of light to make a one-way journey to or from the satellite. Therefore, there is a 0.3 second delay between transmis- sion and reception of the video carrier, independent of ground distance. This delay is not usually a problem for transmission of video security signals; however, this must be kept in mind when synchronization of different incom- ing video signals is required. The signal level reaching the feed horn depends on the size and shape of the antenna (Figure 6-37).

The quality of an antenna is determined by how well it concentrates the radiation intercepted from a target satellite to a single point and by how well it ignores noise and unwanted signals coming from sources other than the target satellite. Three interrelated concepts— gain, beam width, and noise temperature—describe how well an antenna performs. Antenna gain is a measure of how many thousands of times a satellite signal is concen- trated by the time it reaches the focus of the antenna. For example, a typical well-built 10-foot-diameter prime- focused antenna dish can have a gain of 40 dB, which is a factor of 10,000 power gain, which means that the signal is

MICROWAVE TRANSMITTER

ORBITTING SATELLITE

RECEIVER

.15 sec TRANSIT TIME

TRANSIT TIME .15 sec

MICROWAVE

FIGURE 6-36 Satellite video transmission systems

Analog Video, Voice, and Control Signal Transmission 187

SATELLITE DISH

LOW NOISE

AMPLIFIER

EARTH ORBITING SATELLITE

RECEIVING DISH

LOW-NOISE AMPLIFIER

(LNA) LOW LOSS COAX CABLE AMPLIFIER

MONITORING ROOM

VIDEO MONITOR DISPLAY

DOWN CONVERTER

TUNER: UHF VHF

ANTENNA LNA FINE POINTING

MECHANISM

ANTENNA

ANTENNA

FEED HORN

FEED HORN

FIGURE 6-37 Satellite video receiver system

concentrated 10,000 times higher at the focal point than anywhere on the antenna. This gain is primarily depen- dent on the following three factors.

Dish Size. As the size of a dish increases, more radia- tion from space is intercepted. Thus if the diameter of an antenna is doubled, the gain is increased fourfold (four times the area).

Frequency. Gain increases with increasing frequency because higher-frequency microwaves, being closer to the frequency of light, behave a little more like light. Thus they do not spread out like waves in water but can be focused more easily into straight lines like beams of light. Since the gain of a microwave antenna is proportional to the square of the frequency, a signal with twice the fre- quency is concentrated by an antenna with four times the gain. As an example, if the gain is 10,000 when a signal of 5 GHz is received, then it will have a gain of 40,000 at 10 GHz.

Surface Accuracy. Gain is further determined by how accurately the surface of an antenna is machined or formed to exactly a parabolic or other selected shape, and how well the shape is maintained under wind loading,

temperature changes, or other environmental conditions. A good antenna will see only a narrow beam width and will be able to pick out a satellite. A poor-quality dish will see too much extraneous noise and will receive less signal energy from the satellite of interest and pick up unwanted energy.

Dish antennas focus on one earth-orbiting satellite at a time and concentrate the faint signals into a feed horn (waveguide) that directs the microwave signal into a low- noise amplifier (LNA). The LNA amplifies the weak signal by 10,000 times and eventually transmits it by cable to the monitoring location.

Figure 6-37 shows a block diagram of a satellite receiver system. The LNA is the first active electronic component in the receiving system that acts on the video signal. The LNA is analogous to the audio preamplifier in that it provides the first critical preamplification. Its noise characteristics generally determine the quality of the final video image seen on the monitor.

The microwave signal from the LNA is fed via coax- ial cable to a down converter which converts the satel- lite microwave signal to a lower frequency. Since the signal level is still very low, a special low-loss coaxial cable must be used and the signal run must be as short

188 CCTV Surveillance

as possible. Increasing cable run decreases signal level, thereby decreasing the final S/N. The down-converted microwave signal is eventually converted to VHF or UHF and displayed on a television receiver or converted to base- band and displayed on a monitor.

Today most satellite receivers generate a base-band sig- nal containing the base-band video and audio and synchro- nizing information that can be fed directly into a video monitor or recorder. The receiver also outputs a chan- nel 3 or 4 modulated signal for the input to a standard television tuner TV set.

6.5.3.3 Interference Sources

Transmission interference occurs when unwanted signals are received along with the desired satellite signal. Of the several types of interference, perhaps the most com- mon and irritating is caused by the reception of nearby microwave signals using the same or adjacent frequency band. Microwaves reflecting off buildings or even passing cars are responsible for the interference. Very often, mov- ing the microwave antenna several feet can significantly reduce the interfering signal levels.

Other interference includes stray signals from adjacent satellites, or uplink or downlink interference. Finally, a predictable form of interference is caused by the sun. Twice a year the sun lines up directly behind each satellite for periods of approximately ten minutes per day for two or three days. Since the sun is a source of massive amounts of radio noise, no transmissions can be received from satel- lites during these sun outage times. This unavoidable type of interference can be expected during the normal course of operation of an earth satellite station.

6.5.4 Radio Frequency Transmission

Radio frequency (RF) is a wireless video transmission means originally used primarily by government agencies and amateur radio operators. Government frequencies include the 1200 MHz (1.2 GHz) and 1700 MHz (1.7 GHz) bands.

Radio frequency wireless has now found widespread use in commercial security applications in temporary covert and permanent surveillance applications. Video transmit- ters and receivers transmit monochrome or color video signals over distances of several hundred feet to several miles using small, portable, battery-operated equipment. Operating frequencies cover the 150 to 980 MHz, 2.4 GHz, and 5.8 GHz bands.

While RF transmission provides significant advantages when a wired system is not possible, there are FCC restrictions limiting the use of many such transmitters to government applications. Only low-power transmitters are available for commercial applications. Any RF systems used outside the United States require the approval of the

foreign government. Tables 6-7 and 7-5 summarize the channel frequencies available.

6.5.4.1 Transmission Path Considerations

An RF video signal transmission means can follow either commercial broadcasting standards in which the visual signal are amplitude modulated (AM), or noncommer- cial standards that use an FM signal. In the commer- cial standard the audio signal is frequency modulated on the carrier. In both systems the video input signal ranges from a few hertz to 4.5 MHz. For the low-powered transmitter/receiver systems used in security applications, FM modulation has provided far superior performance (increased range and lack of interference) and is the pre- ferred method. The range obtained with an FM RF trans- mitter is from three to four times that of the AM type.

Transmitting at standard commercial broadcast video standards using AM signals and operating on one of the designated VHF or UHF channels is prohibited by the FCC since any consumer-type receiver could receive and display the video picture. This potential is obviously a dis- advantage for covert security surveillance. In the case of FM video transmission, many consumer receivers, though not designed to receive such signals, do display FM signals with some degree of picture quality because of nonlinear and sporadic operation of various receiver circuits. Like- wise, the FCC does not permit the commercial use of FM or other modulation techniques in the commercial VHF and UHF channels.

Low-power RF transmission in the 902–928 MHz, 2.4 GHz and 5.8 GHz ranges have been approved for gen- eral security applications without an FCC license. The 1.2 and 1.7 GHz bands have not been approved for commer- cial use.

6.5.4.2 Radio Frequency Equipment

Many manufacturers produce wireless video RF and microwave links operating in the 900 MHz, 2.4 GHz, and 5.8 GHz frequency bands. This equipment operates on FCC-assigned frequencies with specific maximum transmit- ter output power levels (a few hundred milliwatts). These general-purpose RF links operate at output field strengths 50–250 milliwatts per meter at 3 meters (Part 15 of the FCC specification).

Figure 6-38 illustrates typical RF and microwave video transmission equipments. Figure 6-38a shows two very small, four-channel, low power 1.2 GHz (government use only) and 2.4 GHz transmitters. Any one of four channels can be selected at a time. Figure 6-38b is a small four channel 2.4 GHz transmitter and receiver pair using high- gain Yaggi antennas for increased range and directionality. Figure 6-38c shows a long range 2.4 GHz receiver.

Analog Video, Voice, and Control Signal Transmission 189

BAND FREQUENCY

RANGE (MHz)

UHF

GOVERNMENT, LAW ENFORCEMENT ONLY

VHF—LOWBAND

VHF—HIGHBAND

FM RADIO

SECURITY

54–88

88–108

174–216

470–890

LOW-MEDIUM POWER SEVERAL MILES RANGE

NO RESTRICTIONS, NO FCC LICENSE REQUIRED

COMMERCIAL TELEVISION CHANNELS

2–6

7–13

14–83

SECURITY 350–950 SINGLE CHANNEL

TRANSMITTER/RECEIVER

RESTRICTIONS

902–928

SECURITY

SECURITY

SECURITY

1.2–1.7 GHz

2.4 GHz

5.8 GHz

LOW-MEDIUM POWER

LOW POWER, FCC PART 15 * LICENSE REQUIRED NO RESTRICTIONS, NO FCC

NO RESTRICTIONS, NO FCC LICENSE REQUIRED

LOW-MEDIUM POWER, RANGE UP TO SEVERAL MILES

LOW-MEDIUM POWER, RANGE UP TO SEVERAL MILES

LOW POWER, FCC PART 15

COMMERCIAL RADIO FCC REGULATED

GOVERNMENT, LAW ENFORCEMENT ONLY

GOVERNMENT, LAW ENFORCEMENT ONLY

GOVERNMENT, LAW ENFORCEMENT ONLY

GOVERNMENT, LAW ENFORCEMENT ONLY

ALL SECURITY FREQUENCY BANDS ARE OUTSIDE THE COMMERCIAL TELEVISION BANDS *

INDUSTRIAL, SECURITY, MEDICAL (ISM) **FCC PART 90, 5 WATT MAXIMUM

HIGH POWER, FCC PART 90 **

USAGE

ENFORCEMENT ONLY GOVERNMENT, LAW

2.4 GHzSECURITY

LOW POWER SEVERAL MILES RANGE

—

—

—

—

—

—

—

Table 6-7 RF and Microwave Video Transmission Frequencies

For indoor applications, most RF and microwave trans- mitter/receiver systems use omnidirectional dipole anten- nas for ease of operation. For outdoor operation, dipoles or whip antennas are used. High-gain Yaggi antennas are used to increase range and minimize interference from other radiation sources.

The RF and microwave transmitters and receivers have a standard 75-ohm input impedance; however, they require a 50-ohm coaxial cable at the transmitter output and the receiver input. Using a 75-ohm coaxial cable between the antenna and the transmitter output or the receiver input will seriously degrade the performance of the system even if it is short (1–2 ft). Miniature 50-ohm, RG58U, and RG8 coaxial cables terminated in a small SMA or BNC connec- tor are used.

Figure 6-39 shows the approximate distance between transmitter and receiver antennas (range) versus transmit- ted power, for video transmission. The range values are for smooth and obstacle-free terrain applications using a dipole antenna at the transmitter and receiver. The antennas should be located as high above the ground as possible.

The numbers obtained should be used as a guide only. Actual installation and experience with specific equipment on-site will determine the actual quality of the video image received.

6.5.5 Infrared Atmospheric Transmission

A technique for transmitting a video signal by wireless means uses propagation of an IR beam of light through the atmosphere (Figure 6-40).

The light beam is generated by either an LED or an ILD in the transmitter. The receiver in the optical commu- nication link uses a silicon-diode IR detector, amplifier, and output circuitry to drive the 75-ohm coaxial cable and monitor. The transmitter-to-receiver distance and security requirements of the link determine the type of diode used. Short-range transmissions of up to several hundred feet are accomplished using LED. To obtain good results for longer ranges, up to several miles under clear atmospheric conditions, ILD must be used.

The LED system costs less and has a wider beam, 10–20�

wide, making it relatively simple to align the transmitter and receiver. The beam width of a typical ILD transmitter is 0�1� or 0�2�, making it more difficult to align and requir- ing that the mounting structure for both transmitter and the receiver be very stable in order to maintain alignment. To insure a good, stable signal strength at the receiver, the ILD transmitter and receiver must be securely mounted on the building structure. Additionally, the building struc- ture must not sway, creep, vibrate, or produce appreciable twist due to uneven thermal heating (sun loading).

190 CCTV Surveillance

(B) SMALL TRANSMITTER AND RECEIVER WITH YAGGI ANTENNA

2.4 GHz

4 CHANNEL

POWER OUT: 0.5 W

(A) MINIATURE TRANSMITTER WITH DIPOLE ANTENNA

1.2 GHz, 2.4 GHz.

4 CHANNEL

POWER OUT: 100 mW

(C) RECEIVER WITH DIPOLE ANTENNA

2.4 GHz

FIGURE 6-38 RF and microwave video transmitters

POWER OUT

(WATTS)

RANGE

(Mi)0 1.0 10.0

0.1

1.0

10.0

TYPICAL

TRANSMISSION CONDITIONS: CLEAR AIR, OUTDOOR, NO OBSTRUCTIONS, DIPOLE ANTENNA

0.1

FIGURE 6-39 Transmitter RF power out vs. transmission range

Analog Video, Voice, and Control Signal Transmission 191

TRANSMITTER

LED BEAM DIVERGENCE

DETECTOR RECEIVER FIELD OF VIEW (FOV)

RECEIVER

BUILDING

BUILDING RECEIVER

FIELD OF VIEW (FOV) DETECTOR RECEIVER

BUILDING

TRANSMITTER

BUILDING

CAMERA MONITOR

ILD DIVERGENCE

(0.1−0.2°)

(10−20°)LED IR

IR

IR

ILD IR

FIGURE 6-40 IR atmospheric video transmission system

Both LED and ILD systems can transmit the IR beam through most transparent window glazing; however, glazing with high tin content severely decreases signal transmission, thereby producing poor video quality. The suitability of the window can be determined only by test- ing the system. Since many applications require the IR beam to pass through window panes across a city street or between two buildings, window IR transmission tests should be performed prior to designing and installing such a system.

The primary advantages of the ILD system are long- range (under clear atmospheric conditions) and secure video, audio, and control signal transmission. ILD atmo- spheric links are hard to tap because the tapping device—a laser receiver—must be positioned into the laser beam, which is hard to accomplish undetected.

6.5.5.1 Transmission Path Considerations

Several transmission parameters must be considered in any atmospheric transmission link. Both LED and ILD atmospheric transmission s ystems suffer video signal trans- mission losses caused by atmosphere path absorption.

Molecular absorption is always present when a light beam travels through a gas (air). At certain wavelengths of light, the absorption in the air is so great as to make that wave- length useless for communications purposes. Wavelength ranges in which the attenuation by absorption is tolera- ble are called atmospheric windows. These windows have been extensively tabulated in the literature. All LED and ILD systems operate in these atmospheric windows.

Another cause of light signal absorption is particles such as dust and aerosols, which are always present in the atmo- sphere to some degree. These particles may reach very high concentrations in a geographical area near a body of water. In these locations, improved performance can be achieved by locating the link as high above the ground as possible.

Fog is a third factor causing severe absorption of the IR signal. In fog-prone areas, local weather conditions must be considered when specifying an atmospheric link, since the presence of fog will greatly influence link downtime. Figure 6-41 shows the predicted communication range vs. visibility for a practical LED or ILD atmospheric commu- nications system.

192 CCTV Surveillance

dB

ATMOSPHERIC LOSS FACTORS

ABSORPTION SCATTERING

SCINTILLATION AEROSOLS

0

–10

–20

–30

–40

–50

–60

–70

DISTANCE (Mi)

.5 1 2 3 4 5

ATMOSPHERIC SIGNAL LOSS

FIGURE 6-41 Atmospheric absorption factors and visibility

In addition to signal loss, the atmosphere contributes signal noise, since it exhibits some degree of turbulence. Turbulence causes a refractive index variation in the sig- nal path (similar to the heat waves seen when there is solar heating in air—the mirage effect) and its subsequent wind-aided turbulent mixing. The net effect of this turbu- lence is to move or bend the IR beam in an unpredictable direction, so that the transmitter radiation does not reach the remote receiver. To compensate for this turbulence, the transmitter beam is made wide enough so that it is highly unlikely that the beam will miss the receiver. This wider beam, however, results in lower beam intensity, so the received signal on average will be less than from a narrower beam.

6.5.5.2 Infrared Equipment

The transmitter and receiver used in atmospheric IR transmission systems are very similar to those used in the fiber-optic-cable transmission system (Section 6.3.4). The primary differences are in the type of LED (or ILD) in the transmitter and the optics in both the transmitter and the receiver (Figure 6-42).

The optics in the transmitter must couple the maxi- mum amount of light from the emitter into the lens and atmosphere, that is, to produce the specified beam diver- gence depending on LED or ILD usage. The receiver optics are made as large as practically possible (several inches in diameter) to maximize transmitter beam col-

lection, thereby achieving the highest possible S/N. An example of an atmospheric IR link is shown in Figure 6-43.

The system has a range of approximately 3000 feet and operates at 12 volts DC. For outdoor applications, the transmitter is mounted in an environmental housing with a thermostatically controlled heater and fan, as well as a window washer and wiper.

6.6 WIRELESS CONTROL SIGNAL TRANSMISSION

Signal multiplexing has been used to combine audio and control functions in time-division or frequency-division multiplexing. One system uses the telephone Touch-Tone system, which is standard throughout the world. With this system, an encoder generates a number code correspond- ing to the given switch (digit) closure. Each switch clo- sure produces a dual Touch-Tone signal which is uniquely defined and recognized by the remote receiver station. All that is needed for transmitting the signal is a twisted-pair or telephone-grade line. With such a system, audio and all of the conceivable camera functions (pan, tilt, zoom focus, on/off, sequencing, and others) can be controlled with a single cable pair or single transmission channel. This concept offers a powerful means for controlling remote equipment with an existing transmission path.

It is sometimes advantageous to combine several video and/or audio and control signals onto one transmission

Analog Video, Voice, and Control Signal Transmission 193

ATMOSPHERIC PATH

SILICON DETECTOR LIGHT EMITTING DIODE

(LED)

VIDEO AMPLIFIER

LED DRIVER

LOW- NOISE

AMPLIFIER

VIDEO AMPLIFIER

AND DRIVER

LENS LENS

TRANSMITTER RECEIVER

LENS

LENS Si

DETECTOR

ILD

LENS LED

DIVERGING BEAM

COLLIMATED BEAM

FIGURE 6-42 Block diagram of IR video transmitter and receiver

MONOCHROME, COLOR

RANGE: 1 MILE +

LICENSE REQUIREMENT: NONE TYPE: SIMPLEX (ONE DIRECTION) SIGNAL BANDWIDTH: 5.5 MHz ±1dB, 7 MHz ±3 dB

TRANSMITTER: LIGHT EMITTING DIODE (860–900 nm) PEAK POWER OUTPUT: 30 MW BEAM DIVERGENCE: 3 MILLIRADIANS POWER: AC, 115/220 V, 50/60 Hz, 25 VA

DC, 12 VDC, 12 WATTS

SILICON AVALANCHE DETECTOR FIELD OF VIEW: 3.75 MILLIRADIANS POWER: AC, 115/220 V, 50/60 HZ, 25 VA

DC, 12 VDC, 12 WATTS

VIDEO STANDARD: NTSC, PAL, SECAM (525 TV LINES, 60 Hz OR 625 TV LINES, 50 Hz)

RECEIVER:

60

58

56

54

52

50

48

46

1000 2000 3000 4000 5000 6000 7000

TRANS/REC DISTANCE

(Ff)

VIDEO SIGNAL TO NOISE RATIO (dB)

FIGURE 6-43 IR video transmitter and receiver hardware

194 CCTV Surveillance

channel. This is true when a limited number of cables are available or when transmission is wireless. If cables are already in place or a wireless system is required, the hard- ware to multiplex the various functions onto one chan- nel is cost-effective. Multiplexing of video signals is used in many CATV installations whereby several VHF and/or UHF video channels are simultaneously transmitted over a single coaxial cable or microwave link. In CCTV systems, modulators and demodulators are available to transmit the video control signals on the same coaxial cable used to transmit the video signal.

6.7 SIGNAL MULTIPLEXING/DE-MULTIPLEXING

It is sometimes desirable or necessary to combine sev- eral video signals onto one communications channel and transmit them from the camera location to the moni- tor location. This technique is called multiplexing. Some systems allow multiplexing video, control, and audio sig- nals onto one channel.

6.7.1 Wideband Video Signal

The camera video signal is an analog base-band sig- nal with frequencies of up to 6 MHz. When more than one video signal must be transmitted over a single wire or wireless channel the signals are multiplexed. This is accomplished by modulating the base-band camera signal with an RF (VHF or HF) or microwave frequency car- rier and combining the multiple video signals onto the channel.

6.7.2 Audio and Control Signal

The analog and control signals can be multiplexed with the video signals as sub-carriers on each of the video signals. In the RF band no more than two channels at 928 MHz are practical. In the microwave band at 2.4 GHz up to four channels can be used. At 5.8 GHz up to eight channels can be used.

6.8 SECURE VIDEO TRANSMISSION

When it comes to protecting the integrity of the infor- mation on a signal, high-level security applications some- times require the scrambling of video signals. The video scrambler is a privacy device that alters a television camera output signal to reduce the ability to recog- nize the transmitted signal when displayed on a stan- dard monitor/receiver. The descrambler device restores the signal to permit retrieval of the original video information.

6.8.1 Scrambling

Video scrambling refers to an analog technique to hide, or make covert, the picture intelligence in the picture signal. Basic types include: (1) negative video, (2) moving the horizontal lines, (3) cutting and moving sections of the horizontal lines, and (4) altering or removing the synchronization pulses. All negative video requires that the signal modulator at the camera has some synchronization with the demodulator at the monitoring site.

The key to any analog video scrambling system is to modify one or more basic video signal parameters to pre- vent an ordinary television receiver or monitor from being able to receive a recognizable picture. The challenges in scrambling-system design are to make the signal secure without degrading the picture quality when it is recon- structed, to minimize the increase in bandwidth or storage requirements for the scrambled signal, and to make the system cost-effective.

There are basically two classes of scrambling techniques. The first modifies the signal with a fixed algorithm, that is, some periodic change in the signal. These systems are comparatively simple and inexpensive to build and are common in CATV pay television, as well as in some security applications. The signals can easily be descrambled once the scrambling code or technique has been discovered. It is relatively straightforward to devise and manufacture a descrambling unit to recover the video signal. One of the earliest techniques for modifying the standard video signal is called video inversion, in which the polarity of the video signal is inverted so that a black-on-white picture appears white-on-black (Figure 6-44).

While this technique destroys some of the intelligence in the picture, the content is still recognizable. Some scrambling systems employ a dynamic video-inversion tech- nique: a parameter such as the polarity is inverted every few lines or fields in a pseudo-random fashion to make the image even more unintelligible. Another early technique was to suppress the vertical and/or horizontal synchro- nization pulses to cause the picture to roll or tear on the television monitor. Likewise, this technique produced some intelligence loss, but some television receivers could still lock on to the picture, or a descrambler could be built to re-insert the missing pulses and synchronize the picture, making it intelligible again.

A second class of scrambling systems using much more sophisticated techniques modifies the signal with an algo- rithm that continually changes in some unpredictable or pseudo-random fashion. These more complex dynamic scrambler systems require some communication channel between the transmitter and the receiver in order to pro- vide the descrambling information to the receiver unit, which reconstructs the missing signal. This descrambling information is communicated either by some signal trans- mitted along with the television image or by some separate

Analog Video, Voice, and Control Signal Transmission 195

STANDARD VIDEO

INVERTED VIDEO

SYNC

NEGATIVE VIDEO

SYNC

SYNC

SYNC

VIDEO STANDARD

RANDOMLY CODED

TRANSPOSED SEGMENTS

REASSEMBLED VIDEO

t

SCRAMBLED SIGNAL

SIGNAL UNSCRAMBLED

SYNC

1 2 3 4

96 97

96 9714

97 96

43 21

SIGNAL INVERSION LINE DICING

SEGMENTS

VIDEO SIGNAL

FIGURE 6-44 Video scrambling techniques

means, such as a different channel in the link. The decod- ing signal can be sent by telephone or other means.

In a much more secure technique known as “line dic- ing,” each horizontal line of the video image is cut into seg- ments that are then transmitted in random order, thereby displacing the different segments horizontally into new locations (Figure 6-44). A picture so constructed on a stan- dard receiver has no intelligence whatsoever. Related to line dicing is a technique known as “line shuffling,” in which the scan lines of the video signal are sent not in the normal top-to-bottom image format but in a pseudo- random or unpredictable sequence.

It is often necessary to scramble the audio signal in addition to the video signal, using techniques such as fre- quency hopping adapted from military technology. Sim- ilar to line dicing, this technique breaks up the audio signal into many different bits coming from four or five different audio channels and by jumping from one to another in a pseudo-random fashion scrambles the audio signal. The descrambler is equipped to tune to the differ- ent audio channels in synchronism with the transmitting signal, thereby recovering the audio information.

In the most sophisticated dynamic scrambling systems, utilized for direct-broadcast satellites and multi-channel applications, the video and audio signals are scrambled in a way that cannot be decoded even by the equipment manufacturer without the information from the signal

operator. For example, the audio signal can be digitized and then transmitted in the vertical blanking interval, the horizontal blanking interval, or on a separate sub-carrier of the television signal.

6.8.2 Encryption

Video encryption refers to digitizing and coding the video signal at the camera using a computer and then decod- ing the digitized signal at the receiver location with the corresponding digital decoder. Digital encryption results in a much higher level of security than analog scram- bling. Section 7.7.4 analyzes digital encryption techniques in more detail.

6.9 CABLE TELEVISION

Cable television (CATV) systems distribute multiple chan- nels of video in the VHF or UHF bands using coax- ial cable, fiber-optic cable, and RF and microwave links. Consumer-based CATV employs this modulation– demodulation scheme using a coaxial or fiber-optic cable. The multiplexing technique is often used when video information from a large number of cameras must be

196 CCTV Surveillance

transmitted to a large number of receivers in a network. Table 6-8 summarizes the VHF and UHF television fre- quencies used in these CATV RF transmission systems.

In CATV distribution systems, the equipment accepts base-band (composite video) and audio channels and lin- early modulates them to any user-selected RF carrier in the UHF (470–770 MHz) spectrum. The modulated signal is then passed through an isolating combiner, where they are multiplexed with the other signals. The combined sig- nal is then transmitted over a communications channel and separated at the receiver end into individual video and audio information channels. At the receiver end the signal is demodulated and the multiple camera signals are separated and presented on multiple monitors or switched one at a time (Figure 6-45).

Cable costs are significantly reduced by modulating mul- tiple channels on a single cable. Since the transmission is done at radio frequencies, design and installation is far more critical as compared with base-band CCTV. High- quality CATV systems are now installed with fiber-optic cable for medium to long distances or distribution within a building.

6.10 ANALOG TRANSMISSION CHECKLIST

Transmitting the video, audio, and control signals faith- fully is all important in any security system. This section

itemizes some of the factors that should be considered in any design and analysis.

6.10.1 Wired Transmission

The following checklists for coaxial two-wire UTP, and fiber-optic cable transmission systems show some items that should be considered when designing and installing a video security project.

6.10.1.1 Coaxial Cable

1. When using coaxial cable, always terminate all unused inputs and unused outputs in their respective impedances.

2. When calculating coaxial-cable attenuation, always figure the attenuation at the highest frequency to be used; that is, when working with a 6 MHz bandwidth, refer to the cable losses at 6 MHz.

3. In long cable runs do not use an excessive number of connectors since each conductor causes additional attenuation. Avoid splicing coaxial cables without the use of proper connectors, since incorrect splices cause higher attenuation and can cause severe reflection of the signal and thus distortion.

BAND CHANNEL

DESIGNATION

CATV MID-BAND

CATV SUPER-BAND

CATV HYPER-BAND

J

AA

W 217.25

301.25

169.25

295.25

547.25

121.25

FREQUENCY RANGE PICTURE CARRIER

(MHz)

CH14

CH23 CH26

PPP CH37 CH78

A I

CATV LOW-BAND

CATV MID-BAND

55.25 67.25

91.25 115.25

CATV HIGH-BAND 175.25 211.25

A1A5

CH36CH23

CH99CH95

137

CH2

2 6

NOTE:

AIRWAVE VHF TV CHANNELS 2–6 OPERATE FROM 55.25–83.25 MHz

AIRWAVE UHF TV CHANNELS 7–13 OPERATE FROM 175.25–211.25 MHz

AIRWAVE FM STATIONS OPERATE FROM 88.1–107.9 MHz

CH6

CH22

Table 6-8 Allocated CATV RF Transmission Frequencies

Analog Video, Voice, and Control Signal Transmission 197

MULTIPLE VIDEO

CAMERAS

MULTIPLEXER

SIGNALS

ALL SIGNALS TRANSMITTED

OVER ONE WIDEBAND

MICROWAVE CATV (RF)

FIBER OPTIC

MULTIPLEXER DE-MULTIPLEXER

MULTIPLE MONITORS

DE-MULTIPLEXER

SEPARATES CAMERA

SIGNALS

OUTPUT DEVICES • SWITCHER • MONITOR • DVR / VCR • PRINTER

COMBINES CAMERA

SWITCHER

o

o o

VIDEO TRANSMISSION

LINK

AUDIO/ VIDEOAUDIO/ VIDEO

AUDIO/ VIDEO

M1

M2

MN

C1

C2

CN

• • •

FIGURE 6-45 Multiplexed video transmission system

4. For outdoor applications, be sure that all connectors are waterproof and weatherproof; many are not, so consult the manufacturer.

5. Try to anticipate ground loop problems if unbalanced- coaxial-cable video runs between two power sources are used. Use fiber optics to avoid the problem.

6. Using a balanced coaxial cable (or fiber-optic cable) is usually worth the increased cost in long transmission systems. When connecting long cable runs between sev- eral buildings or power sources, measure the voltage before attempting to mate the cable connectors. Be careful, since the voltage between the cable and the connected equipment may be of sufficient potential to harm you.

7. Do not run cable lines adjacent to high-power RF sources such as power lines, heavy electrical equipment, other RFI sources, or electromagnetic sources. Good earth ground is essential when working with long trans- mission lines. Be sure that there is adequate grounding, and that the ground wire is eventually connected to a water pipe ground.

6.10.1.2 Two-Wire UTP

1. Choose a two-wire twisted-pair having approximately 1 twist for 1–2 inches of wire.

2. Choose a wire gauge between 24 AWG (smallest) and 16 AWG.

3. Choose a reputable UTP transmitter/receiver manu- facture. Either have the manufacture supply technical specifications showing performance over the distance required or test the product first.

4. Will the UTP transmitter/receiver be powered from the camera or separate 12 VDC power supply?

6.10.1.3 Fiber-Optic Cable

1. Consider the use of fiber optics when the distance between camera and monitor is more than a few hun- dred feet (depending on the environment), if it is a color system, and if the camera and monitor are in different buildings or powered by different AC power sources.

2. If the cable is outdoors and above ground, use fiber optics to avoid atmospheric disturbance from lightning.

3. If the cable run is through a hazardous chemical or electrical area, use fiber optics.

4. Use fiber optics when a high-security link is required.

6.10.2 Wireless Transmission

The following checklists for RF, microwave, and IR trans- mission systems should be considered when designing and

198 CCTV Surveillance

installing a video security. The wireless video transmission techniques require more careful scrutiny because of the many variables that can influence the overall performance and success of the system.

6.10.2.1 Radio Frequency (RF)

1. How many channels does the system require? At 928 MHz the maximum number of channels is two to avoid crosstalk between channels.

2. Are all cameras approximately in the same location? If in different locations the crosstalk is minimized.

3. RF transmission is susceptible to external electri- cal interference. Are there probable interferences in the area?

4. Range is a function of the transmitter power and inter- vening atmosphere and objects (buildings, trees, etc.). Is there a line of sight between the transmitter and the receiver?

5. Is the transmission path indoors or outdoors? 6. For indoor transmission, reflection and absorption of

all objects must be taken into consideration. RF trans- mission does not penetrate metal objects and is partially absorbed by other materials.

7. For outdoor transmission, obstructions such as trees, buildings, etc. must be considered.

6.10.2.2 Microwave

1. How many channels does the system require? At 2.4 GHz the maximum number of channels is four and for 5.8 GHz is 8 if crosstalk between channels is to be avoided.

2. Are all cameras approximately in the same location? If they are in different locations the crosstalk is minimized.

3. Microwave transmission is susceptible to external inter- ference from other microwave or noise sources. Are there probable interferences in the transmission path?

4. Range is a function of the transmitter power and inter- vening atmosphere and objects (buildings trees, etc.). Is there a line of sight between the transmitter and receiver? If not metal panels can be used to redirect the microwave transmission.

5. Is the transmission path indoor or outdoor? 6. For indoor transmission, reflection and absorption of

metal objects must be taken into consideration, as well

as other building materials. Microwave energy does not transmit through metal objects and only partially through nonmetal.

7. For outdoor transmission, obstructions such as trees, buildings, etc. must be considered.

6.10.2.3 Infrared

1. Infrared transmission is very sensitive to the intervening atmosphere. Dust, fog, and humidity play an impor- tant role in the transmission and cause absorption and scattering of the IR signal.

2. Is there a line of sight between the IR transmitter and receiver; no obstructions?

3. Can a mirror be used to “see around a corner”? 4. Are the transmitter (most important) and receiver units

mounted on a sturdy nonvibrating mounting. Are the buildings stable and motionless under high wind, and over full sun loading conditions?

5. Is secure transmission needed?

6.11 SUMMARY

Video signal transmission is a key component in any CCTV installation. Success requires a good understanding of transmission systems.

Most systems use coaxial cable, but fiber-optic cable is gaining acceptance because of its better picture quality (particularly with color) and lower risk factor with respect to ground loops and electrical interference. In special situations where coaxial or fiber-optic cable is inappro- priate, other wired or wireless means are used, such as RF, microwave, or light-wave transmission. For very long range applications, non-real-time slow-scan systems are appropriate.

Many security system designers consider cabling to be less important than choosing the camera and lens and other monitoring equipment in a CCTV application. Often they attempt to cut costs on cabling equipment and installation time, since they often make up a large frac- tion of the total system cost. Such equipment is not visible and can seem like an unimportant accessory. However, such cost-cutting can drastically weaken the overall system performance and picture quality.