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Coaxial cable cannot be ignored

2021-05-28

Coaxial cable cannot be ignored

 

For copper cable testing, we discussed a lot about balanced twisted-pair copper cabling related content, such as Category 6 (CAT 6), Category 6 (CAT 6A) and Category 8 (CAT 8). Although this type of cabling is widely used to support Ethernet transmission of voice, data, and video, it does not mean that it is the only type of copper cabling you may encounter.

Coaxial Cable ("coax" in short) has long been used to transmit data and video signals. It is one of the first media to support 10BASE2 and 10BASE5 Ethernet, which can achieve 10 Mb up to 185 meters or 500 meters, respectively. /s transfer. 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. The cable 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.

Although we usually think that coaxial cable is only used in broadband video and cable television (CATV) home applications, but in the commercial enterprise environment, from closed circuit television (CCTV), audio and video to radio frequency antennas, and even some network connections, you can find Its figure. Therefore, it is very necessary to understand this cable medium and how to test it.

Main type

There are many different 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 applications such as CCTV and CATV 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 indoor 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 should be noted that all components in the coaxial cable system should have the same impedance to avoid 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 up to 69 meters, while the 734 type cable has a coverage distance of up to 137 meters. RG6 cable can also be used to transmit DS3 signals, but the coverage distance is shorter.

For any coaxial cable, successful installation depends on the use of high-quality components and correct installation techniques, especially the installation of connectors. Insertion loss is affected by the total length of the installed link and is the main parameter to ensure that the coaxial cable supports the intended application.