Cable for closed circuit television monitoring system (CCTV)
Video signal transmission is generally used in the form of direct modulation technology to baseband frequency (about 8MH bandwidth), the most commonly used transmission medium is coaxial cable. Coaxial cable is specially designed to transmit video signal, its frequency loss, image distortion, image attenuation amplitude are relatively small, can be very good to complete the task of transmitting video signals. General domestic use of solid core PVC insulated coaxial cable series SYV-75 common type SYV-75-5 (the video signal transmission distance is 500 meters), distance, coaxial cable SYV-75-7, SYV-75-9 or SYV-75-12 (in actual engineering, the thick cable transmission distance can reach more than 1000 meters); also by adding a video amplifier to enhance video brightness, chroma and synchronous signal, but the circuit interference signal will be amplified, so the loop cannot connect a video amplifier too much, otherwise it will lead to the distortion of the image saturation image; farther by using optical fiber transmission, optical fiber transmission with small attenuation, wide frequency band, without a series of advantages of electromagnetic wave interference, light weight, good secrecy, mainly for national and provincial trunk Communication network, cable television network and high speed broadband computer network. In the closed circuit television monitoring system, optical fiber transmission has become the preferred mode of long distance video and audio and control signal transmission.
The video signal can also be transmitted by the data cable (twisted pair), which is used for the transmission equipment of the twisted pair. In some special applications, twisted pair transmission equipment is essential. Such as when building has according to the integrated wiring standard equipped with a large number of twisted pair (standard category 5 cables or 5E line) and in the room left with corresponding information interface (or RJ45 RJ11), the new CCTV surveillance equipment need not re wiring, depending on the audio signal and the control signal can be transmitted through the twisted pair, the video signal transmission will use a twisted pair transmission equipment. In addition, the image of the front end video camera is required to be transmitted to the control room equipment in the application situation of the front end video camera, and the transmission equipment of the twisted pair cable is needed. Twisted pair video transmission equipment is at the front end will be suitable for unbalanced transmission (i.e. suitable 75Ohm coaxial cable to transmit) the video signal is converted to a video signal for balanced transmission (i.e. for twisted pair transmission); in contrast with the front-end processing at the receiver through twisted pair video signal back into a non balance of video signals. Twisted pair transmission equipment itself has the function of video amplification, so it is suitable for long distance video transmission. For the above different transmission mode, the use of transmission components and transmission lines are different. Communication cable is generally used in the configuration has an electric pan, electric lens imaging device, when in use to remote control decoder installed in the field. Field decoder and the control center of the video matrix switch between the host communication transmission cable, the general use of 2 core shielded cable (RVVP, each core cross-sectional area of 0.3~0.5mm2) or 3 twisted pair (UTP). The basic principle of choosing the communication cable is the longer the distance, the greater the area. For example: RS-485 communication provides the basic communication distance is 1200m, but in the actual project in the use of 2X1.5 RVV of the sheath line communication length can be extended to more than 2000 meters. When the communication distance is too long, it is necessary to use the RS-485 communication repeater.