Brief introduction of coaxial cable by Hangzhou right angle Cable Technology Co., Ltd

Coaxial cable can be used for analog signal and digital signal transmission. It is suitable for a variety of applications, among which the most important are television transmission, long-distance telephone transmission, short-distance connection between computer systems and LAN. As a means of transmitting TV signals to thousands of households, coaxial cable has developed rapidly, which is cable TV. A cable TV system can load dozens or even hundreds of TV channels, and its transmission range can reach tens of kilometers. For a long time, coaxial cable is an important part of long-distance telephone network. Today, it faces increasingly fierce competition from optical fiber, ground microwave and satellite.

The development of coaxial cable is mainly divided into four generations: the first generation began to use polyethylene as solid core insulation medium in the mid-19th century; The second generation uses chemical foaming PE material as insulating medium; The third generation is the lotus root core longitudinal hole PE material as the insulating medium; The fourth generation uses physical foaming PE material as insulating medium. According to the structure, coaxial cable can be divided into leakage coaxial cable, multi-core coaxial cable, fine diameter coaxial cable and composite coaxial cable.

The development of coaxial cable industry has experienced a series of changes. As the global electronic industry entered its peak in 2000, as a part of the electronic industry, the coaxial cable market also reached a historical peak. In the following three years, as the global economic growth rate entered a trough, the coaxial cable industry also entered a downturn with the contraction of downstream demand, and there was no sign of recovery until the second half of 2003. Since 2004, the global coaxial cable industry has entered a new round of growth. With the continuous expansion of mobile communication signal coverage, the expansion of the number of base stations, and the continuous improvement of mobile signal requirements in transportation, energy, medical and other fields, the market development prospect of the global RF coaxial cable industry is still promising.

working principle:

The coaxial cable is divided into four layers from inside to outside: central copper wire (single strand solid wire or multi strand stranded wire), plastic insulator, mesh conductive layer and wire sheath. The central copper wire and the mesh conductive layer form a current loop. It is named because the central copper wire and the reticular conductive layer are coaxial.

Coaxial cables conduct alternating current rather than direct current, which means that the direction of current is reversed several times per second.

If ordinary wires are used to transmit high-frequency current, this wire will be equivalent to an antenna transmitting radio outward. This effect consumes the power of the signal and reduces the strength of the received signal.

Coaxial cable is designed to solve this problem. The radio emitted by the central wire is isolated by the mesh conductive layer, which can control the emitted radio by grounding.

There is also a problem with coaxial cable, that is, if a certain section of the cable is greatly squeezed or twisted, the distance between the central wire and the mesh conductive layer is not consistent, which will cause the internal radio waves to be reflected back to the signal transmission source. This effect reduces the acceptable signal power. To overcome this problem, a layer of plastic insulator is added between the central wire and the mesh conductive layer to ensure the consistent distance between them. This also leads to the characteristics that the cable is relatively rigid and not easy to bend.

In essence, the shielding material of coaxial cable is mainly to improve the external conductor. From the initial tubular external conductor, it has developed into single-layer braiding and double-layer metal. Although the shielding performance of the tubular outer conductor is very good, it is not easy to bend and inconvenient to use. The shielding efficiency of single-layer braiding is the worst. The transfer impedance of double-layer braiding is three times lower than that of one-layer braiding. It can be seen that the shielding effect of double-layer braiding is much better than that of single-layer braiding. Each Datong axis cable manufacturer is constantly improving the outer conductor structure of the cable to maintain its performance.

Main classification:

Coaxial cable can be divided into two basic types, baseband coaxial cable and broadband coaxial cable.

Baseband coaxial cable

The shielding layer of baseband coaxial cable is usually a mesh structure made of copper, and its characteristic impedance is 50 Ω. The cable is used to transmit digital signals. The commonly used models are rg-8 (thick cable) and rg-58 (thin cable). The most intuitive difference between thick cable and thin cable is that the cable diameter is different. Thick cable is suitable for relatively large local networks, with long standard distance and high reliability; However, the thick cable network must be installed with transceiver and transceiver cable, which is also difficult to install, so the overall cost is high. On the contrary, the thin cable is relatively simple and the cost is low; However, due to the need to cut off the cable during installation, it is easy to produce the hidden danger of poor contact when there are many joints.

Whether the network is connected by thick cable or thin cable, the fault point often affects all machines on the whole cable, and the fault diagnosis and repair are very troublesome. Therefore, baseband coaxial cable has been gradually replaced by unshielded twisted pair or optical cable.

Broadband coaxial cable

The shielding layer of broadband coaxial cable is usually stamped with aluminum, and its characteristic impedance is 75 Ω. This kind of cable is usually used to transmit analog signals. The common model is rg-59. It is a standard transmission cable used in cable TV network. It can transmit multiple TV signals in one cable at the same time. Broadband coaxial cable can also be used as the transmission medium of some computer networks.

Advantages and disadvantages:

The advantage of coaxial cable is that it can support high bandwidth communication on relatively long repeater free lines, and its disadvantages are also obvious: first, it is large, and the diameter of thin cable is 3 / 8 inch thick, which takes up a lot of space in cable duct; Second, it cannot withstand entanglement, pressure and serious bending, which will damage the cable structure and prevent signal transmission; Finally, the cost is high, and all these shortcomings can be overcome by twisted pair. Therefore, in the current LAN environment, it has been basically replaced by the Ethernet physical layer specification based on twisted pair.

Application:

In CATV transmission, coaxial cable is widely used in medium and small transmission systems because of its low cost and easy construction. Especially in the "last mile" transmission of HFC (hybrid fiber coaxial) network, it can not be replaced by other cables. Many passive components, active components and users need cable connection. Impedance matching must be achieved between all components connected with coaxial cable. If not matched, the signal will be reflected between components and cables, increasing the impact of noise and ghosting on the transmitted image.