Good video transmission design is a very important part of video monitoring system. If the construction of a set of good system chosen is able to produce or image processing high quality of the camera, camera, monitor, video recorders, but without good transmission system, finally on the monitors will not be able to see the image is satisfactory. According to "bucket law," the final image quality will depend on the whole a worst part of the system; And the worst of the ring is usually transmission system. The system design and installation personnel must according to the actual need to choose the right means of transmission, high quality transmission lines and equipment, and installation in accordance with professional standards, to achieve the ideal effect of transmission.
Direct modulation technology, commonly used video signal transmission in baseband frequency (about 8 MHZ bandwidth), in the form of coaxial cable is the most common transmission medium. Coaxial cable is designed to transfer the video signal, the frequency of losses, image distortion and image attenuation of the amplitude is small, can be a very good to complete the task of video signal. Generally adopts special SYV75 ohm coaxial cable series, commonly used models for SYV75-5 (it WuZhongJi of video signal transmission distance is usually 300-500 - m); When far away, need to adopt SYV75-7, SYV75-9 even SYV75-12 of coaxial cable (in actual engineering, hawser WuZhongJi transmission distance can be more than 1 km); Also have by adding video amplifier in order to enhance brightness, chroma and synchronization of the video signal, but line interference signals can be amplified, too much so loop can't concatenated video amplifier, otherwise there will be a saturated now like, leads to the distortion of the image; Farther way of using optical fiber transmission, optical fiber transmission with attenuation is small, width, are not affected by electromagnetic interference, light weight, good secrecy and a series of advantages, it is mainly used for national and provincial trunk communication network, cable network and high-speed broadband computer network. And in a closed circuit television monitoring system, optical fiber transmission has also become a long audio and preferred way of control signal transmission.
Can also use twisted pair video signal transmission, which will use twisted-pair transmission equipment. In some special applications, twisted pair transmission equipment is necessary. By integrated wiring standard such as, when the building is equipped with a large number of twisted pair (standard according to the three kinds of lines or five line) and in all the information related to the room with the corresponding interface (RJ45 and RJ11), the new CCTV surveillance equipment when it does not need wiring, audio signals and control signals can be fixed by twisted-pair cable to transmit, the video signal transmission will use twisted-pair transmission equipment. In addition to already equipped with a twisted pair (or two core sheathed wire) and the image of the front camera is controlled to the equipment applications, also need to the twisted pair transmission equipment. The function of the twisted pair video transmission equipment is on the front end will be suitable for non-equilibrium transport (75 Ω coaxial cable transmission) or to the video signal is converted into a suitable balance of transmission (i.e., suitable for twisted pair transmission) of video signal; At the receiving end is contrary to the front-end processing, video signals coming through twisted-pair to convert video signal of non equilibrium. Twisted-pair transmission equipment itself has the video amplification effect, and therefore suitable for long distance transmission of signals. Used by different means of transport to above, the transmission components and transmission lines are quite different.
Communication cables in the configuration is commonly used in electric yuntai, electric lens camera device, when use should be installed at the scene of remote control decoder. The decoder and control center of video matrix switching host communication between the transmission cable, generally USES the core block communication cable (RVVP) 2 or 3 kind of twisted pair UTP, each core cross-sectional area was 0.3 ~ 0.5 was. Choose the communication cable is the basic principle of the longer the distance, the larger the wire diameter. RS - 485 communication rules, for example, the basic communication distance is 1200 m, but in the practical engineering chooses RVV2 1.5 sheathed wire communication can be extended to more than 2000 m length. When the communication distance is too long, need to use the RS - 485 communication repeater.
Control cable is usually refers to the variable lens is used to control the haeundae and power of multi-core cable, it is connected to one from the controller or haeundae decoders, electric lens control terminal, the other end is directly to the yuntai, electric lens to the corresponding terminal. Due to dc or ac voltage control cable is provided, and the average distance is very short (and sometimes less than 1 m), basically there is no interference, so there is no need to use the shielded wire. Most of the commonly used control cable using 6 or 10 core cable, as, RVV10 RVV6-0.2-0.12, etc. Six core cable joint respectively in yuntai of up, down, left, right, automatic, six public terminal, 10 core cable, in addition to answer the yuntai six terminal include electric lens changing times, focus, aperture, public four terminals. In a closed circuit television monitoring system, from the decoder to yuntai and lens control cable due to the distance between the short generally do not make special requirements; And is controlled by the controller to the yuntai and electric lens distance is less dozens of meters, more than a few hundred meters, the control cables will need to have certain requirements, namely the wire diameter to coarse, if choose RVV10 0.5, RVV10 0.75, etc.
Four commonly used audio monitor cable core block communication cable (RVVP) or 3 kind of twisted pair UTP, each core cross-sectional area was 0.5. In the absence of interference environment, can also be selected as the unshielded twisted pair, such as the five types of commonly used in integrated wiring twisted-pair (4 to 8); Due to monitor and control system in the central control room to monitor head of audio signal is used in a point-to-point wiring way, with a high voltage low current transmission, so the use of block 2 core cable, such as RVV2-0.5.