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Guide to Closed Circuit TV (CCTV)

So would you like to play "Spot the CCTV Camera?". Eagle eyed visitors may recognise the profusion of street furniture, surrounding a single heritage dome camera keeping watch over part  of Londons' prestigious Oxford Street shopping area.

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Copper Cable Transmission - Balanced 'Twisted Pair'

The other main category of copper cable used, particularly iin larger commercial systems, is ‘balanced’ twisted pair transmission.

The signal propogation actually works in a slightly different way, with two parallel twisted conductors being used to carry the video signal.

Once again, the thickness of the conductors will dictate the cables ability to carry any given signal, but whereas ‘unbalanced’ co-ax can be used successfully for some distance without any additional equipment, ‘balanced’ twisted pair cables must have the appropriate launch or receiver (or both) units in order to recover a displayable signal. Nowadays, a very limited number of cameras are available with balanced output connections, rather than simply the conventional 'BNC' socket for co-axial cable.

Although far less susceptible to induced signal problems, Twisted pair cables are available in ‘shielded’ or ‘unshielded’ (UTP) versions, choice ultimately being according to their intended locations. They are generally used with passive (unpowered) 'baluns' for short cable runs, and 'active' (powered) devices for longer distances.

Multiple pair cables can be economically installed at much lower cost than the equivalent co-ax (and in a far smaller space), although the cost of launch and balancing equipment also needs to be carefully considered.

In practice, these technologies are generally only applied for cable runs over 200 metres, and perhaps up to 2000 metres or so. In addition to standard ‘twisted pair cables’ there are other varient transmission units which can also be supplied for use with very low cost unshielded multicore ‘telephone’ type, and category 5 (CAT 5 & 5E) cables.

These newer transmission systems, along with the emerging ‘Network’ options, are likely to become increasingly popular over the next few years, particularly within larger commercial premises, although not necessarily for all the right reasons.

Fibre optic transmission systems>

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