The most widely used cables in surveillance and security projects include coaxial cables, twisted pairs, and optical fibers. The following are the main points of knowledge about the usage methods and functions of these commonly used cables, as well as the differences between them.
Coaxial cable is a cable with a central copper conductor wrapped in layers of insulated wires. It is characterized by good anti-interference ability, stable data transmission, and low price. It is also widely used, such as closed-circuit television lines. Coaxial thin cables are generally sold at a few yuan per meter in the market, which is not too expensive. Coaxial cables are used to connect with BNC connectors. The coaxial cables sold on the market are generally finished products that have been connected with BNC connectors.
In engineering practice, in order to extend the transmission distance, a coaxial amplifier is used. The coaxial amplifier can amplify the video signal to a certain extent, and can also compensate different frequency components in different sizes through equalization adjustment, so as to minimize the distortion of the video signal output by the receiving end. However, coaxial amplifiers cannot be cascaded indefinitely. Generally, only 2 to 3 coaxial amplifiers can be cascaded in a point-to-point system. Otherwise, the video transmission quality cannot be guaranteed and adjustment is difficult. Therefore, when using coaxial cables in a monitoring system, in order to ensure a better image quality, the transmission distance range is generally limited to about 400-500 meters.
In addition, coaxial cables still have some shortcomings in the transmission of image signals in the monitoring system:
1) The coaxial cable itself is greatly affected by climate change, and the image quality is affected to a certain extent;
2) The coaxial cable is relatively thick, which is not convenient for wiring in dense monitoring applications;
3) Coaxial cables generally can only transmit video signals. If the system needs to transmit control data, audio and other signals at the same time, additional wiring is required;
4) Coaxial cable has limited anti-interference ability and cannot be used in strong interference environment;
5) The coaxial amplifier also has the disadvantage of difficulty in adjustment.
2. Ethernet Cable Twisted cable
5) CAT5 cable: This type of cable has increased winding density, a high-quality insulation material, and a transmission rate of 100MHz. It is used for voice transmission and data transmission with a maximum transmission rate of 100Mbps. It is mainly used for 100BASE-T and 10BASE-T network. This is the most commonly used Ethernet cables.
6) CAT5 cable: CAT5 has low attenuation, less crosstalk, higher attenuation to crosstalk ratio (ACR), signal-to-noise ratio (Structural Return Loss), smaller delay error, and performance Greatly improved. The maximum transmission rate of CAT5E cable is 250Mbps.
7) CAT6 cable: The transmission frequency of this type of cable is 1MHz～250MHz, and the comprehensive attenuation crosstalk ratio (PS-ACR) of Category 6 wiring system should have a larger margin at 200MHz. It provides two times the power of CAT5 bandwidth. The transmission performance of Category 6 cabling is much higher than that of the Super Category 5 standard, and is most suitable for applications with a transmission rate higher than 1Gbps.
An important difference between CAT6 and CAT5 is: improved crosstalk and return loss performance. For a new generation of full-duplex high-speed network applications, excellent return loss performance is extremely important. The basic link model is canceled in the six types of standards, and the wiring standard adopts a star-shaped topology. The required wiring distance is: the length of the permanent link cannot exceed 90m, and the channel length cannot exceed 100m.
8)CAT6A Cable: CAT6A Cable is an improved version of Category 6, which is also an unshielded twisted pair cable specified in ANSI/EIA/TIA-568B.2 and ISO Category 6/Class E standards. Mainly used in gigabit networks. In terms of transmission frequency, it is also 200-250 MHz like Category 6 lines, and the maximum transmission speed can also reach 1 000 Mbps, but it is greatly improved in terms of crosstalk, attenuation and signal-to-noise ratio.
9) CAT7 Cable: This line is the latest twisted pair in the ISO 7/F standard. It is mainly used to adapt to the application and development of 10 Gigabit Ethernet technology. But it is no longer an unshielded twisted pair, but a shielded twisted pair, so its transmission frequency can reach at least 500 MHz, which is more than twice that of CAT 6 and CAT6A cables. Up to 10 Gbps.
3. Optical fiber
Optical fiber (Fiber Optic Cable) transmits signals in the form of light pulses, so the material is mainly glass or plexiglass. It consists of a fiber core, a cladding and a protective cover.
The structure of the optical fiber is very similar to that of a coaxial cable, and the center is an optical fiber made of glass or transparent plastic, surrounded by a protective material, and multiple optical fibers can be combined in one optical cable as needed. According to different optical signal generation methods, optical fibers can be divided into single-mode fibers and multi-mode fibers. To
Multimode fiber is generally used for network connections in the same office building or in a relatively close area. The single-mode optical fiber transmits data with higher quality and longer transmission distance, and is usually used to connect office buildings or geographically dispersed networks. If optical fiber and cable are used as the network transmission medium, it is necessary to add equipment such as optical transceivers, so the cost investment is greater and it is less used in general applications.
The biggest feature of optical fiber is that it conducts optical signals, so it is not interfered by external electromagnetic signals, and the signal attenuation speed is very slow, so the signal transmission distance is much longer than the above various network cables that transmit electrical signals, and it is especially suitable for Places with harsh electromagnetic environment.
Due to the optical reflection characteristics of optical fiber, multiple signals can be transmitted at the same time inside an optical fiber, so the transmission speed of the optical fiber can be very high. At present, the 1Gbps 1000Mbps optical fiber network has become the mainstream high-speed network. Theoretically, the optical fiber network can reach up to 50000Gbps 50Tbps. speed.