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Video signal can be transmitted in analog or digital form. Analog video signal takes the band spreading from 50 Hz to a few MHz. For its transmission in CCTV circuits, coaxial cables are mostly used, with 75 ohm impedance. Generally, all devices being components of a transmission line are prepared for connecting with this type of cable, using BNC connectors.
Basic parameter that characterizes the usefulness of a medium for analog transmission is its bandwidth i.e. the difference between the upper and lower frequencies for which the irregularity of the amplitude of the transmitted signal is not higher than 3 dB.
Besides that, the important parameters that characterize cables are:
- wave impedance - voltage to current ratio in any place of the cable, when there are no reflections, i.e. in condition of ideal matching. On account of minimal attenuation and popularity, 75 ohm cables are widely used with most CCTV equipment.
- reflection factor - it is ratio of amplitude of reflected wave to primary wave. Use in an installation of not-uniform cable or other elements with different impedance effects in appearing reflected waves that distort the original signal.
- wave attenuation - describes decrease of signal amplitude along the cable, which is caused by transformation of electromagnetic energy into heat and increases with frequency. High influence on attenuation has diameter of the central conductor (the bigger diameter the lower attenuation) and type of isolation (the best are made with polypropylene and polythene). For example, the cable CTF-167 has attenuation 1.6 dB/100m at 50 MHz (for other cables it may reach even 15 dB/100m).
- shielding effectiveness - resistance to induction of disruptive voltages in cable coming from external sources of electromagnetic radiation. The shield of a coaxial cable is made of good conductor, usually braided copper (sometimes tinned or silver-plated). The braided screen ensures good shielding effectiveness combined with good flexibility of the cable.
For digital transmissions the parameter deciding about transmission ability is bit rate - it informs how many bits can be transferred within one second. Usual coaxial cable ensures transmission with bit rate around 600 Mbps, modern twisted-pair 5CAT cable - to 100 Mbps; for fiber optics this speed reaches 10 Gbps.
Digital video transmission can be performed using computer twisted-pair cable and, however within some limited range, with the use of telephone cable. Generally conversion from analog to digital signal and compression is used. This kind of solution also allows to use telephone line as transmission medium, however it can't guarantee real time transmission (unless using xDSL service). Together with development of digital registration the meaning of signal transmission in computer networks increases, however we should remember that not every network ensures satisfying quality of transmission. Color camera generates around 160 Mbps data stream, it can be reduced a few dozen times after compression, anyway transmission of such a dense information stream may be hard in existing networks, it's worth to consult the idea of network video transmission with administrator of the network.
Generally coaxial cables fulfill requirements of CCTV transmission over distances up to 1km. Above this distance, we should consider the use of twisted-pair or fiber optic cable, which, even if much more expensive, ensures the best transmission quality and insensitiveness to interferences.
Caution: The best effects can be achieved with copper cables (having copper inner wire as well as shield made with copper braid). For longer distances one should choose cables with thicker inner conductor and good shielding effectiveness. For baseband video applications the cables with steel wire covered with copper are not suitable, even though they have good parameters for high RF bands.
Where to use PE, PVC, FRHF and gel-filled cables?
- cables with PE (polyethylene) sheath. Polythene is flammable and flame spreading material, therefore it shouldn't be used inside buildings. Addition of antioxidants, soot or pigments immunizes polythene to advert effects of atmospheric conditions (e.g. UV radiation), therefore the cables are used outdoors.
- cables with PVC sheath. Their advantage is quite high fire resistance and no flame spreading. However, they can emit large quantity of smoke and hydrogen chloride. Anyway, some types of them are characterized by low smoke and gas emission during burning process and they should especially be used in indoor solutions.Our offer here
- cables with FRHF covering. No-halogen materials, no flame spreading (FRHF - Flame Retardant Halogen Free), they don't exude aggressive smoke. Safety regulations increasingly require using these cables in indoor solutions.Our offer here
- gel-filled cables. To secure cable against humidity influence, metal tape is usually used - its permeability for humidity is much less than plastics. Much better parameters for these applications has copper tape rather than aluminum. However, it is also essential penetration along the cable. To reduce it, the cables are filled with special hot-pumped gel. These cables can be buried underground.Our offer here
The most popular cables used in CCTV systems
Coaxial cables.
Used for video transmission from a camera in the case when power is supplied separately. We achieved distance 600m using copper cable TRISET-113 E1015_500
Used for video transmission from a camera in the case when power is supplied separately. We achieved distance 600m using copper cable TRISET-113 E1015_500
The cable which can be led underground is WDXPEX 75-1.15/5.0 E1034_100 (gel-filled).
Structure of the cable CAMSET 100 75-0.59/3.7+2x1.0
Twisted-pair cables.
These cables consist of 4 pairs, which are wires or cords with 0.5 mm diameter. Apart from LAN networks, they are commonly used in CCTV installations, allowing to transfer video signal and power through one cable. We should note that, with a long cable, voltage drop can make it impossible for a camera to work. Therefore, it is important to perform calculations, defining maximal distance between the camera and power supply adapter. More information about twisted-pair cable parameters and calculation example can be found here.
These cables consist of 4 pairs, which are wires or cords with 0.5 mm diameter. Apart from LAN networks, they are commonly used in CCTV installations, allowing to transfer video signal and power through one cable. We should note that, with a long cable, voltage drop can make it impossible for a camera to work. Therefore, it is important to perform calculations, defining maximal distance between the camera and power supply adapter. More information about twisted-pair cable parameters and calculation example can be found here.
There are a few different twisted-pair transmission devices in our offer. They have different functions: video, audio transmission, data and video signal transmission. You may view our catalog pages, they describe functions of relevant devices in details:
- M1662 - audio/video transformer (transmitter/receiver) TR-2P+2AUM16661- video transformer TR-1M1667 - video transformer TR-4/4M1668 - TRN-1/400 video transformer - transmitterM1669 - TRO-1/400 video transformer - receiver
Available twisted-pair cables:
- UTP 5e (unshielded) - E15111_305
- FTP 5e (shielded by overall foil) - E1515_305
- FTP LSOH (non-flammable - not spreading fire). Used in places requiring highest security standards
- UTP PE - E15101_100 - outdoor UTP PE gel-filled cable. Special sheath allows to lead the cable underground.
Twisted-pair cable
Fiber optic transmission systems, due to very low attenuation, immense throughput, full resistance to outer electromagnetic field, no outwards emission of energy are ideal solutions for transmitting multiple signals / data over longer distances. However, their use in CCTV is limited by costly additional converters changing electric signal to optic signal and vice versa.
Optical fiber types:1. Multi-mode, MMF - Multi Mode Fiber
- gradient (graded)
- step
Multi-mode optical fiber
Single-mode optical fiber
Gradient optical fiber
Graded or gradient optical fiber, in opposite to step one, has fluently changing refraction factor. In practice, because of technological reasons, it has a few thousand layers, what imitates fluent change of refraction factor. Its use eliminates blurring of optical signal. Thanks to it, in comparison with step optical fiber, this kind of cable has increased bandwidth. Step optical fibers are practically not used nowadays. Single-mode optical fiber features almost no mode dispersion, as it practically propagates only one light ray inside.
