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Cameras
Analog cameras are a key component of a traditional video surveillance solution. They capture
images in the environment and convert them to analog video. Each surveillance environment has
unique camera and positioning requirements. Installing a camera in the proper environment (with
proper lighting, field of view and power) can be one of the most challenging tasks of implementing
the solution.
Selecting the proper camera for the system also is important. A wide variety of cameras are
available to meet specific deployment requirements. These devices include cameras with PTZ
functionality, day/night capabilities, vandal-resistance, weather-proofing, and many other features.
Serial PTZ data can be transmitted either in a point-to-point fashion or by using a multidrop bus.
With a multidrop bus, cameras can be configured with unique system dome IDs and can be daisy-
chained by using the same set of electrical wires.
Transmission Media
To transmit video signals from analog cameras, different media can be used. Coaxial cable is one
of the most common cable types, but twisted pair and fiber optic cable have also become popular.
Coaxial Cable
A coaxial cable consists of a center conductor that is protected by an insulating spacer and a
shield, which in most cases consists of a metallic web of conductors. The entire assembly is
wrapped with a plastic insulating layer. Proper cable selection and installation is important because
cable-related issues are the most common cause of video problems in a CCTV installation.
All coaxial cables have characteristic impedance. CCTV equipment typically uses coaxial cable
with impedance of 75 Ohms. Cables are available in different Radio Guide (RG) types. RG
specifies how radio frequency signals travel through a 75 Ohm coaxial cable. Table 1 lists the
typical RG cables that are used in CCTV environments.
Table 1.
Coaxial Cable Types
Type
RG-6/U
RG-11B/U
RG-59B/U
RG-59 is one of the most commonly used cables because it is small in diameter and easy to work
with. RG-11 is the largest in diameter and harder to work with, but it supports longer distances.
Fiber Optic Cable
Fiber optic cable is relatively new in CCTV installations, but it has quickly become popular because
it can span longer distances and accommodate more bandwidth than coaxial cable. Advantages of
fiber optic cable include:
●
Wider signal frequency bandwidth than coaxial cable.
●
Ability to carry light-modulated signals for longer distances than coaxial cable.
●
Immune to nearby signals and electromagnetic interference (EMI), so it provides a lower bit
error rate.
●
Multiple signals can travel on a single fiber with distances beyond 2,000 feet.
Impedance (Ohms)
Diameter (mm)
75
6
75
10
75
6.15
Design Guide
Distance (feet)
1,000–1,500
2,000–2,500
750–1,000
1-2
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