The transmission of video and data over 'conventional' copper cables can no longer keep pace with today's ever growing needs for higher quality signals at faster rates over longer distances. The problem is that coax and twisted pair cables exhibit a build up of resistance and impedance which limits the distance that signals can flow. David Archer, technical manager, Fiber Options, comments on how fibre-optics are an elegant and cost-effective solution to the high bandwidth requirements of CCTV.
Running conductors over long distances causes any system to act like a giant aerial, picking up interference from a variety of sources, including crosstalk from adjacent conductors, induced currents from stray magnetic fields, and other extraneous sources of electrical noise.
Fibre-optics offers an elegant and cost effective solution to all these problems. Fibre has a wider bandwidth and lower transmission loss characteristic than coax, permitting high definition pictures to be transmitted over very long distances without the use of in-line amplifiers or repeaters. And because the signal is transmitted as a beam of light rather than an electric current, the system is totally immune to any form of electrical interference, including that from adjacent conductors or even high voltage power lines.
On the downside, handling a glass fibre approximately the same size as a human hair will never be as easy as joining two wires with a screw terminal block, and of course cleanliness is vital. Furthermore, additional electronic interfaces are required at each end of the link to provide the conversion from electrical signals to light and vice versa.
Why is it then that, despite these reservations, there is an ever growing interest in the use of fibre-optics for CCTV and related security applications?
Benefits of fibre-optics transmission
Fibre-optic transmission offers a wide range of benefits to many types of user. However, not all of these are of equal significance to all users and the most important ones for CCTV applications are summarised below:
* Low transmission loss. Low loss fibre-optic cables permit the transmission of CCTV signals over large distances without in-line amplifiers or repeaters. This is particularly useful for long haul transportation schemes such as motorway and railway surveillance systems, where unrepeatered links in excess of 20 km are not uncommon.
* High bandwidth transmission capability. The high bandwidth of optical fibres permits large numbers of high quality video, audio and data signals to be transmitted simultaneously over each optical fibre.
* Immunity to interference and crosstalk. Their total immunity to external electrical interference or crosstalk results in trouble free installations, even where the installer has failed to pay sufficient attention to the location of adjacent power cables, etc.
* Electrical isolation. The non-conductive properties of fibre cables means that problems caused by variations in earth potentials, such as are found in power stations and electrified railways schemes, are avoided. This same feature also prevents equipment damage caused by current surges from lightning strikes, etc.
* Lightweight small size cables. The very small size of optical fibres and cables will often give overcrowded ducts a further lease of life. For example, the space occupied by one coaxial cable may be replaced by a fibre-optic cable containing, say, 24 fibres, each of which could conceivably carry as many as 64 simultaneous video and 128 audio or video signals.
Future-proof medium
Fibre-optic networks may be upgraded to carry a greater volume of traffic simply by changing the terminal transmission equipment, not the fibre. Alternatively, part or all of the network may be used for a completely different application, allowing, for example, a mixture of computer LAN and CCTV traffic in the same cable.
For more information contact Elvey Security Technologies, 011 401 6700, [email protected], www.elvey.co.za
Elvey Security Technologies is the sole recognised distributor of Fiber Options equipment in South Africa, Fiber Options being one of the leading brands of fibre-optic transmission equipment. This equipment has been installed in high profile sites such as Johannesburg International Airport, mines, CBDs and nuclear power stations to name but a few.
| Tel: | +27 11 401 6700 |
| Email: | [email protected] |
| www: | www.elvey.co.za |
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