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  • On the choice of cable in the security video surveillance system


        Video transmission design is a very important part of the video surveillance system. If a construction is a good system selected are able to generate high-quality screen IP cameras, lenses, monitors, VCRs, but without a good transmission system, the final image on the monitor will not be able to satisfactorily . Under the "bucket rule", the final image quality will depend on the worst part of the whole system; but the worst part is often the transmission system. System designers and installers must select the appropriate transmission mode according to actual needs, the quality of the transmission cable and equipment, according to professional standards for installation, in order to achieve the desired transmission.
        Video signal transmission is generally by direct modulation technique in the form of base-band frequency (about 8MHz bandwidth), the most common transmission medium is a coaxial cable. The coaxial cable is specifically designed to be used to transmit video signals, the frequency of loss, image distortion, the image attenuation of the amplitude is relatively small, can complete the task of the transmitted video signal. Commonly used the dedicated SYV75 ohm series coaxial cable, commonly used models for no relay transmission distance SYV75-5 (its video signal is generally 300-500m); distance, the need to adopt SYV75-7 SYV75-9 even SYV75-12 coaxial cable (in the actual project, the Culan no relay transmission distance up to 1km); also to enhance the video brightness, chroma and synchronizing signals by increasing the video amplifier, but line interference signals will be amplified, so the loop can not be connected in series too many video amplifier, it will lead to the phenomenon of saturation, resulting in image distortion; longer distances using fiber optic transmission, fiber optic transmission with low attenuation, frequency bandwidth, from electromagnetic interference. light weight, and the confidentiality of a series of advantages, primarily for national and provincial and municipal backbone communication networks, cable networks and high-speed broadband computer network. CCTV surveillance camera system, the optical fiber transmission has become the preferred way of audio and control signal transmission over long distances.
        The video signal can also use the twisted pair transmission, which use the twisted pair transmission equipment. In some special applications, twisted pair transmission equipment is essential. For example, when the building has been laying the cabling standards a lot of twisted-pair (standard three types of lines or five lines) and left the room information interface (RJ45 or RJ11), the new increase the closed-circuit television monitoring equipment do not need to re-wiring, video and audio signals and control signals can be transmitted over twisted pair, in which the transmission of video signals is necessary to use the twisted pair transmission equipment. In addition to the already laid a twisted pair (or two core sheathed cable) and the need to spread the image of the front-end network camera equipment in the control room applications, also used as a twisted pair transmission equipment. Twisted pair video transmission capabilities of the device is in the front-end for non-equilibrium transport (ie, for a 75Ω coaxial cable), video signals are converted into video signals suitable for balanced transmission (ie, for twisted-pair transmission); at the receiving end. opposite to the front-end processing, the video signal coming through the twisted pair to convert unbalanced video signals. Twisted pair transmission equipment, video amplification, and thus suitable for long-distance signal transmission. The above transmission, used transmission parts and transmission lines are quite different.
        Communication cables for general use electric head, power lens of the camera device in the configuration required when using the remote control decoder installed in the field. The scene decoder and the control center video matrix switching of communication transmission cable between the host, generally 2-conductor shielded communication cable (RVVP) or Category 3 twisted-pair UTP, cross-sectional area of ​​each core is 0.3mm ² ~~ 0.5mm ². The basic principle is to select the communications cable the longer the distance, the greater the diameter. For example: RS-485 communication provisions of the basic communication distance is 1200m, but in the actual project selection RVV2-1.5 of the sheathed wire communication length extended to more than 2000m. When the communication distance is too long, use the RS-485 communication repeater.
        Control cable is often referred to as multi-core cable is used to control PTZ and electric variable lens, connect one end of the head of the controller or decoder, motorized lens control terminal, the other end directly to the head, the electric the corresponding terminals on the lens.
        The control cables provide DC or AC voltage, and generally very short distance (sometimes less than 1m), basically there is no interference problem, so there is no need to use shielded wire. The mostly commonly used control cable with 6-core or 10 core cable, such as RVV6-0.2 RVV10-0.12. 6-cell cable connected to the PTZ, down, left, right, automatic, six public terminals, 10-core cable in addition to the 6 terminal, then head also includes power lens zoom, focus, aperture public four terminals. CCTV surveillance camera system, from the decoder to the control cable between the PTZ IP camera lens due to the relatively short distance and generally do not make any special requirements; control to pan the Central Control Room and electric lens distances ranging from tens of m, more than a few hundred meters on the control cable will need to have certain requirements, namely the diameter to be rough, such as the selection RVV10-0.5, RVV10-0.75.
        Sound monitoring cables generally use 4 core shielded communication cable (RVVP) or Category 3 twisted pair of UTP per core cross-sectional area of ​​0.5mm ². Interference-free environment, an optional non-shielded twisted pair, such as commonly used in integrated wiring, Category 5 twisted-pair (4 to 8 cores); audio signals to the control room monitoring system to monitor head using point-to-point wiring, high voltage low current transmission using unshielded 2-core cable can, such as RVV2-0.5 and so on.

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