A coaxial cable ("coax" in English) is a cable composed of two coaxial, mutually insulated cylindrical metal conductors to form a basic unit (coaxial pair), and then a single or multiple coaxial pairs. It has been used to transmit data and video signals for a long time.
It is one of the first media to support 10BASE2 and 10BASE5 Ethernet, which can achieve 10 Mb/s transmission up to 185 meters or 500 meters, respectively. The term "coaxial" means that the central conductor of the cable and its shield have the same axis or center point. Some coaxial cables may have multiple shielding layers, such as a four-shielded coaxial cable, which contains two layers of shielding, and each layer of shielding is composed of aluminum foil wrapped with wire mesh. The shielding characteristics of coaxial cable make it have strong anti-electromagnetic interference ability and can transmit high-frequency signals over long distances. There are many different types of main types of coaxial cables that support a wide range of professional applications, such as satellite communications, industrial, military and marine applications. The three most common types of non-industrial coaxial cables are RG6, RG11 and RG59, of which RG6 is most commonly used in CCTV and CATV applications in corporate environments. The center conductor of RG11 is thicker than RG6, which means that its insertion loss is lower and the signal transmission distance is longer.
However, thicker RG11 cables are more costly and very difficult to bend, which makes them unsuitable for deployment in internal applications, but more suitable for long-distance outdoor installations or straight backbone links. RG59 is more flexible than RG6, but its loss is higher. It is rarely used in other applications except for low-bandwidth, low-frequency analog video applications (rear-view cameras in automobiles) with short distances and limited wiring space. Coaxial cables also have different impedances-usually 50, 75, and 93 Ω. 50 Ω coaxial cables have high power handling capabilities and are mainly used in radio transmitters such as amateur radio equipment, civil band radio (CB) and walkie-talkies. 75 Ω cables can maintain signal strength well and are mainly used to connect various types of receiving equipment, such as cable television (CATV) receivers, high-definition televisions and digital video recorders. 93 Ω Coaxial cable was used in IBM mainframe networks in the 1970s and early 1980s, with very few applications and expensive. Although the 75 Ω coaxial cable impedance is most commonly encountered in most applications today, it is important to note that all components in the coaxial cable system should have the same impedance to avoid possible signal loss and signal loss at the connection point. Internal reflections that reduce video quality. The digital signal 3 (DS3) signal used in the central office (also known as T3 line) transmission service also uses coaxial cables, including 75 Ω 735 type and 734 type. The 735 type cable has a coverage distance of 69 meters, while the 734 type cable has a coverage distance of 137 meters. RG6 cable can also be used to transmit DS3 signals, but the coverage distance is shorter.