Talking about the Application of Cable Products in Security System

The video signal transmission generally adopts the direct modulation technology, transmits in the form of the base band frequency (about 8MHz bandwidth), the most common transmission medium is the coaxial cable. Coaxial cable is specially designed to transmit video signals. Its frequency loss, image distortion, and image attenuation are relatively small, which can well complete the task of transmitting video signals. The domestic use of solid-core PVC insulated RF coaxial cable SYV-75 series, the commonly used model is SYV-75-5 (its non-relay transmission distance for video signals is generally 500 meters), when the distance is far, the use of Coaxial cable of SYV-75-7, SYV-75-9 and even SYV-75-12 (In practical projects, the thick cable has an unrelayed transmission distance of more than 1000 meters); there are also video enhancement amplifiers to enhance the video The luminance, chrominance and synchronization signals, but the interference signal in the line will be amplified, so too many video amplifiers cannot be connected in series in the loop, otherwise saturated images will appear, leading to distortion of the image; the optical fiber transmission method will be used farther away. Optical fiber transmission has a series of advantages such as small attenuation, wide frequency band, no electromagnetic interference, light weight, and good confidentiality. It is mainly used in national and provincial-level backbone communication networks, cable television networks, and high-speed broadband computer networks. In the closed-circuit television monitoring system, optical fiber transmission has also become the preferred method for long-distance video, audio and control signal transmission.

Internationally used coaxial cable for video systems are RG series, JIS series, etc.

Video signals can also be transmitted using data cables (twisted pair), which requires twisted pair transmission equipment. In some special applications, twisted pair transmission equipment is essential. For example, when a large number of twisted pairs (Class 5 or Category 5e) in the building have been laid out in the building and the corresponding information interfaces (RJ45 or RJ11) are left in the relevant rooms, the new CCTV monitoring equipment does not require wiring, video and audio signals and control signals can be transmitted through the twisted pair, in which the transmission of video signals requires the use of twisted pair transmission equipment. In addition, twisted-pair transmission equipment is also required for applications where twisted-pair cables (or two-core sheathed cables) have been laid and front camera images need to be transmitted to central control room equipment. The function of the twisted pair video transmission equipment is to convert the video signal suitable for unbalanced transmission (that is, suitable for 75Ω coaxial transmission) to the video signal suitable for balanced transmission (that is, suitable for twisted pair transmission) at the front end; The reverse processing of the front end converts the video signal transmitted through the twisted pair into an unbalanced video signal. The twisted pair transmission device itself has a video amplification effect and is therefore also suitable for long distance video transmission.

For the above different transmission methods, the transmission components and the transmission lines used are quite different. The communication cable is generally used in an imaging device equipped with an electric pan/tilt head and an electric lens, and a remote control decoder needs to be installed at the site during use. The communication transmission cable between the on-site decoder and the video matrix switching host of the control center generally uses a 2-core shielded cable (RVVP, a cross-sectional area of ​​0.3~0.5 mm2 per core) or a Category 3 twisted pair (UTP). The basic principle for selecting a communication cable is that the longer the distance, the larger the cross-sectional area. For example: The basic communication distance that RS-485 communication stipulates is 1200m, but in actual project choose RVV 2X1.5 sheath wire to expand the communication length to more than 2000 meters. When the communication distance is too long, an RS-485 communication repeater is required.

The control signal cable usually refers to a multi-core cable used to control the pan/tilt and the electric variable lens. One end of the control signal cable is connected to a pan/tilt and an electric lens control terminal of a controller or a decoder, and the other end is directly connected to the pan/tilt, On the corresponding terminals of the electric lens. Since the control cable provides DC or AC voltage, and the distance is usually very short (sometimes less than 1 meter), there is basically no interference problem, so no shielded cable is needed. Commonly used control cables mostly use 6- or 10-core cables, such as AVVR 6X0.2 and AVVR 10X0.12. The 6-core cable is connected to the top, bottom, left, right, automatic, and public 6 terminals of the PTZ respectively. In addition to the 6 terminals of the PTZ, the 10-core cable includes the zoom, focus, and aperture of the motorized lens. , Public 4 terminals. In the CCTV system, the control cable from the decoder to the pan/tilt head and the lens does not require special requirements due to the relatively short distance; however, the distance from the controller of the central control room to the pan/tilt head and the electric lens is as small as several tens of meters. For a few hundred meters, there are certain requirements for the control cable, that is, the cross-sectional area should be large, such as RVV 10X0.5, RVV 10X0.75, etc.