About RG-58 coaxial cable

Coaxial cable can be divided into baseband coaxial cable and broadband coaxial cable (i.e. network coaxial cable and video coaxial cable). Coaxial cables are divided into 50Ω baseband cables and 75Ω broadband cables. Baseband cables are divided into thin coaxial cables and thick coaxial cables. Baseband cables are only used for digital transmission, and the data rate can reach 10Mbps. Broadband cable is a standard used in CATV system, which can transmit analog signals and digital signals through frequency division multiplexing. Coaxial cable is more expensive than twisted pair, but its anti-interference performance is better than twisted pair. Need to connect more equipment, when the communication capacity is quite large, you can choose coaxial cable. Coaxial cable is a cable composed of coaxial core conductors insulated from each other inside and outside: the inner conductor is copper wire and the outer conductor is copper tube or mesh. The electromagnetic field is enclosed between the inner and outer conductors, so the radiation loss is small and it is less affected by external interference. It is usually used to transmit multiple telephones and televisions. The name of coaxial cable is related to its structure. Coaxial cable is also one of the most common transmission media in LAN. The conductor pair used to transmit information is selected according to the structure that the cylindrical outer conductor is sheathed outside the inner conductor (thin core) and the two conductors are isolated from each other by insulating materials. The center of the outer conductor and the core line of the central shaft are on the same axis, so it is called coaxial cable. The coaxial cable is designed in this way to prevent external electromagnetic waves from interfering with the transmission of abnormal signals. Coaxial cables can be divided into thick coaxial cables and thin coaxial cables according to their diameters. Thick cable is suitable for relatively large LAN, with long standard distance and high reliability. Because there is no need to cut off the cable during installation, the network access position of the computer can be flexibly adjusted as needed. However, the installation of the thick cable network is difficult, so the overall cost is high. On the contrary, the installation of thin cables is relatively simple and the cost is low. However, because the cable needs to be cut off during installation, both ends must be equipped with basic network connectors (BNC) and then connected to both ends of T-connector, so when there are too many connectors, it is easy to produce bad hidden dangers, which is one of the most common faults of Ethernet in operation at present. Both thick and thin cables are bus topologies, that is, one cable connects multiple machines. This topology is suitable for machine-intensive environment, but when one contact fails, it will affect all machines on the whole series cable. Fault diagnosis and maintenance are very troublesome, so it will be gradually replaced by unshielded twisted pair or optical cable. The advantage of coaxial cable is that it can support high-bandwidth communication on relatively long lines without repeaters, but the disadvantages are also obvious: first, the diameter of thin cable is 3/8 inch, which takes up a lot of cable duct space; Second, it cannot withstand winding, pressure and severe bending, which will damage the cable structure and hinder signal transmission; Finally, the cost is high, and these shortcomings can be overcome by twisted pair, so in the current LAN environment, it has basically been replaced by Ethernet physical layer specification based on twisted pair. Coaxial cables are divided into thin cables? RG-58 and thick cable? RG- 1 1。 The diameter of thin cable is 0.26 cm, the maximum transmission distance is 185 m, and the terminal resistance is 50 Ω? As shown in Figure 5, the T-connector (as shown in Figure 6) and BNC connector are connected to the network card, so the wire price and connector cost are relatively cheap, and there is no need to buy equipment such as hubs, which is very suitable for building a small Ethernet with centralized terminal equipment. The total cable length should not exceed185m, otherwise the signal will be seriously attenuated. The impedance of the thin cable is 50 Ω. The diameter of the thick cable (RG- 1 1) is 1.27 cm, and the maximum transmission distance reaches 500 meters. Because of its rather thick diameter and poor elasticity, it is not suitable for erection in narrow indoor environment. Moreover, the manufacturing method of RG- 1 1 connector is complicated, so it can't be directly connected to a computer. It needs to be converted into an AUI connector through an adapter and then connected to a computer. Because the strength of thick cable is stronger than that of thin cable and the maximum transmission distance is longer, the main purpose of thick cable is to play the role of network backbone and connect several networks composed of thin cable. The impedance of thick cable is 75 Ω. Video coaxial cable is abbreviated as SYV in English, and there are often 75-7, 75-5, 75-3, 75- 1 and other models, and its characteristic impedance is 75 ohms to adapt to different transmission distances. It is the main medium for transmitting video signals in asymmetric baseband mode. The main application fields are: equipment bracket connection, closed circuit television (CCTV), antenna system (MATV) for transmitting color or monochrome radio frequency monitors. These applications do not require the selection of precision video coaxial cables with particularly strict electrical tolerances. The characteristic resistance of video coaxial cable is 75 ohms, which is not randomly selected. Physics has proved that the best attenuation characteristic of video signal appears at 77 ohms. In low power applications, the material and design determine that the optimal impedance of the cable is 75 ohms. Standard video coaxial cable has solid conductor and multi-strand conductor. It is suggested to use multi-conductor design in some applications that need to bend cables, such as the internal connection between CCTV cameras and tray and bracket devices, or the transmission cable of remote cameras.