Welcome to the
"Technical Section"
Doktor Jons

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 - Unbalanced Co-ax

Co- axial cables can be used for distances well in excess of a thousand metres, although signal 'launch' and 'balancing' equipment will need to be employed to help maintain the overall picture quality.

With any co-axial cable there is always the possibility of ‘picking up’ another externally transmitted signal, or 'hum', (always try and avoid running co-ax alongside heavy weight mains cables!) which can be reduced to some degree using launch amplifiers and receivers, but can more simply be minimised by selecting a high quality ‘double screened’ cable.

This type has in addition to the normal stranded outer layer (copper braid), an additional highly efficient ‘screen’ layer which can be comprised of a tightly woven braid, or preferably an overall lapping of thin copper foil. Although standard 'BNC' connectors are readily available in both solder, crimp and twist on versions, double screened cable connectors are generally far more difficult to obtain (incidentally, given the choice Doktor Jon would recommend the solder connectors everytime; they may take longer to fit, and require a little bit more skill, but their longterm reliability simply cannot be matched).

It's perhaps worth quickly mentioning that only copper braid cables should be used for CCTV, and aluminium braid versions should really be avoided. Ideally depending on the cable run, a braiding which provides at least a 90% coverage should be selected.

For specialist applications, or where long cable lengths are to be pulled through complex ducting, steel wire armoured versions are available, or at a more basic level, heavy duty ‘plastic armoured’ cables, with a high density polyethelyne outer layer designed to protect the inner ‘workings’.

For cables needing to be taken overhead, best practice suggests that a proper 'catenary' support arrangement should be put in place, to prevent any strain to the coax. Wherever the cable is run, water or moisture must never be allowed to enter the cable, as this will adversely affect its transmission capabilities, and ultimately render it absolutely useless.

Although the vast majority of CCTV systems have historically used, and indeed continue to use unbalanced co-axial cable, as the cheapest and most practical for everyday applications, it is not without its limitations.

So for longer distance, or multiple signal distribution using copper cable transmission, balanced 'twisted pair cable may provide the answer>.

The unique "TRUSTED" National CCTV Improvement Campaign

IMPORTANT: No material may be reproduced, copied or redistributed from this site,
without the express written consent of doktorjon.co.uk

All the detailed information on this site is provided in good faith; and as such, Doktor Jon
does not accept responsibility for any consequential loss, injury or disadvantage
resulting from any individual or organisation acting on the details contained herein.

© doktorjon.co.uk 2004 - 2008

Homepage...:...Gateway...:...Technical Gateway....:....Quickfind Index....:....Equipment Directory
Site Index...:...About this site....:....CCTV Helpdesk....:.... The Forum ....:....Contact Doktor Jon