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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.

The complete A to Z ...
... on getting pictures from A to B!

Copper Cable Transmission

Since the earliest days of communication when Mr Bell decided to give someone a ring (possibly Mrs. Bell?), copper cable has been the preferred option for making those all important calls. Nowadays, Closed Circuit Television systems the world over, rely on basic copper technology simply to get the pictures from A to B.

There are actually two main techniques in use, although one in particular is responsible for the vast majority of signal links. Unbalanced video transmission relies on the use of a 75 Ohm (impedence) co-axial cable to carry the signal between two different pieces of equipment.

Available in various grades, the central conductor thickness generally dictates how long the length of cable can be, before internal resistance and the effects of attenuation (degradation), puts paid to its effective use as a transmission medium. Engineers generally regard signal propogation as a very ‘Black and White’ situation; a particular cable will work up to ‘x’ distance and no further, and yet it's actually a lot more complex than they'd have you believe.

The most basic co-axial cable used is type URM 70 which is characterised by having a multi stranded central conductor. Whilst being less efficient than a solid conductor, it does however present a slight advantage for cameras mounted on moving platforms, such as minipan or pan and tilt heads (scanners), as the constant movement is less likely to result in the inner conductor ‘snapping’ under stress.

The next grade of cable is RG 59 B/U; effectively the industry standard. Using a solid central copper conductor, this durable cable is quite capable of transmitting colour signals over a couple of hundred metres. It’s perhaps worth mentioning that the resistance of the cable, and the attenuation (induced signal degradation) that results, will still allow an acceptable Black and White signal to travel many hundreds of metres (the visible effect being a pronounced ‘softening’ of the picture contrast), although the colour or ‘chroma' signal would have long since been wiped out.

There are various higher grades of cable which in general terms are characterised by a steady increase in the diameter of the central conductor (e.g. from 1mm for RG 59B/U, to 1.25mm or 1.67mm in diameter), which as well as providing a significant improvement in transmission capabilities, also represents a considerable increase in unit cost.

More information on Copper video cables >>

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