Using Fiber Optic Cable For CCTV Applications

Introduction

When using Fiber Optic cable for CCTV systems, there are a several variables to consider that will determine how the system can be designed. In general the surrounding network equipment is what will dictate your overall design topology. Using Fiber Optic cable as a transmission medium will allow for longer distance runs without signal degradation. The following factors need to be taken into consideration when designing a system of this type: camera type (IP or Analog) fixed and IP, terminal equipment, available space, and required power. The following will go into detail about the possible solutions and the requirements for each case.

Camera Type and Network Equipment

When designing a CCTV system using multiple cameras run over a Fiber Optic cable there will be a difference in equipment between using Analog or IP based cameras. When converting the cameras signal from an electrical signal to a pulse of light different equipment is used to make that conversion.

Analog Solution

In the figure on the next page you will see that a transmitter and receiver are used to convert the electrical signal to light and back to electrical again. The converting equipment (VOS-8000FT and VOS-8000FR) must be used as a pair, in order to distinguish between the different camera signals being sent across the fiber line. The fiber cable can be a multimode or single mode, single strand cable. Multimode fiber maxes out at 2 km in distance. The number of analog cameras one can use would be limited by the converting transceiver pair. In the figure below 8 analog signals are being converted and transmitted over a single fiber line. Based on this equipment one could use 8 analog cameras per strand of fiber. However, if you were to convert your analog signal to digital before reaching the fiber cable one could use a switch to network multiple analog cameras before sending the data across the fiber line. Your next limitation becomes the amount of space you have for the network equipment and cable. This applies for standard as well as PTZ cameras. For PTZ cameras your converting equipment must support any additional features such as a control and audio signals.

IP Solution

In an IP or digital solution there are multiple topologies that can be used in networking the peripheral equipment. The general methodology will remain the same. Convert the electrical signal to an optical signal in the fiber cable and back to an electric signal at your control room. The difference is that you will use a media converter that converts from network cable such as CAT6 to fiber instead of converting from coaxial to fiber as in the analog solution. You may also use a single fiber switch in place of the media converters depicted below. This is possible because you are using Ethernet protocol and the switch will automatically convert the signal from the network cable to the Fiber cable (the signal remains digital). The limit to the number of cameras you could use again becomes the amount of space you have for terminal/network equipment.

Power

For analog cameras, local DC or AC power will be required for the cameras adapter to be plugged into. PTZ cameras usually require more power than fixed cameras for the motor functions to operate. Standard fixed cameras often run on 12V DC, while PTZ cameras operate on 24V DC.

For IP cameras the above remains true, however you have the option to use Power over Ethernet (PoE). When providing power directly over the network cable it can be generated at the switch or in midspan with a PoE injector. PoE uses two protocols for supplying power, Mode A and Mode B. Either case uses 2/4 pairs of the UTP cable with Mode A using different pairs than Mode B for the power.

About The Author:

Nick Quinlan is a graduate of UCF in engineering and a content creator for Supreme Electric & Solar out of Dallas, Texas.