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This feature is triggered by movement within an image on one or more cameras. Some recorders also have the facility to set up certain areas of the screen to pick up movement only. If, in an office, for example, you wanted to record movement around a particular desk only, you can select this area and eliminate all others.

This is useful in cases where only a limited amount of storage is available: the recorder will only start recording when there is movement – and stop when the movement stops. It is also useful if you only want to record actual 'events'. You may, for example, have a CCTV system recording 24 hours a day, seven days a week, but how much of the recording will be relevant? With VMD enabled, the cameras will only activate upon movement, so when you review the recorded images, you won't be wasting time looking through hours of footage of blank walls.

Obviously, this is no good in an environment where there is constant movement, such as shopping arcades, playgrounds etc, but is very useful in areas of high sensitivity where any movement needs to be monitored.

Another way of using VMD is to have two different record settings for day and night.

In a shop, for example, you may want to record everything during the day but, out of hours, there is the option to set the recorder to record on VMD only so that you are not wasting storage space.

If there is a break-in during the night, VMD will be triggered and the images recorded.

Switch appeal
Q: What is a day/night switch?
A: This device allows users to switch between day and night settings. If not already built-in, it can be retrofitted to a recorder. For example, if you wanted alarms connected to your recorder to become active at night only, you can set the switch so that the recorder activates upon an alarm being triggered. Even better, if this is linked to your alarm panel, your recorder will switch automatically to night mode when the alarm panel is armed. This is useful for recording alarms as you can programme your recorder to increase the record rate upon an alarm being received.

Shaking all over
Q: Why do images I have recorded on one of my cameras shake when playing back?
A: This is usually down to the camera rather than the recorder. If this only happens on one camera, swap it with another camera. If the problem still occurs, try looking at the connections and the camera mounting.

Black and blue
Q: I have an image on screen but there are also thick black and blue bars. Is it my camera?
A: This could be an issue with the video signal being received. For example, if the signal is over 1 Volt pk-pk, you can try decreasing this level (normally done by turning the gain pot slightly down in the equaliser). Also check that the cable run has not been wired into Balanced Input.

n.b. This is only applicable if you are using coax to twisted pair converters.

Terminator too
Q: I can just about see the image on my cameras – some of them are very bright, others very dark. Why is this?
A: This sounds like it could be an issue with termination. CCTV products have to be terminated to 75 Ohms. If the terminations are set incorrectly, picture quality will deteriorate dramatically. The start of the video signal (the camera) is terminated to 75 Ohms, therefore the last device on the end of the cable also has to be terminated to 75 Ohms (usually a monitor or a CCTV multiplexer).

Normally there are two positions on the rear of the equipment (for example a monitor) – Hi Z means high impedance, and this setting is used if the monitor is looping out to another monitor in the chain. If, however this is the only monitor or the last monitor in the chain, the equipment needs to be set to 75 Ohms.

There be ghosts
Q: I want to lengthen my coaxial run. Can I use choccy-block or do I need a special connection?
A: I would never advise using choccy block! Every joint in a cable produces a change in impedance and, more often than not, a loss in signal. If the joints are also poorly made, the picture will produce a 'ghosting' effect as a result. A better way is to use the correct BNC connections to maintain the integrity of the cable.