Larger CCTV systems have multiple cameras, which can be viewed and controlled from a number of monitoring positions.

These systems are usually implemented by connecting all the cameras and monitors to a central video switching matrix unit. This is a large-capacity video switcher, which allows any camera input signal to be routed to any number of monitor outputs. This is often referred to as an ‘active cross-point matrix’. A typical matrix has a minimum of 32 video inputs and 8 monitor outputs.

Monitor outputs will have the option of time, date and camera identification information superimposed on the CCTV picture using ‘On-Screen Display’ (OSD).

Multiple operator positions will be supported with a priority system to define what happens in the incident of two operators requesting control of the same camera simultaneously. Normally there is no limit to how many operators can view a picture from the same camera. However, it is possible to define which system cameras an operator can see and control.

The matrix can also be equipped with a number of auxiliary control ports, which multiplexers and video recorders, for example can be connected.

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When designing or working with CCTV systems always remember the video signal coming from the camera is only 1 volt peak-to-peak. As a result it is easily interfered with by external signals, easily lost or attenuated resulting in poor picture quality and noisy pictures.

In order to obtain good quality pictures there are a number of standard rules to follow:

Don’t exceed the following distances when installing the coaxial cable. Acceptable distances for common types of coaxial cable:

Always ensure each video signal is terminated only once and the terminator resistor is at the end of the cable. This will maintain the signal amplitude at 1V and minimise ghosting as a result of reflections.

Most of the time, signals are terminated automatically. However, take care when a signal is leading to more than one piece of equipment for instance a telemetry transmitter and video multiplexer. When ‘looping through’, always ensure the termination resistors (often denoted as ‘Hi-Z’) are switched off.

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