When it comes to copper testing, we talk a lot about category balanced twisted-pair copper cabling like Category 6, Category 6A and Category 8. And although this cabling type is widely deployed to support everything Ethernet transmission of voice, data and video, that doesn’t mean it’s the only copper cabling you could encounter.
Coaxial cabling (sometimes just “coax” for short) has long been used for distribution of data and video signals, and it was one of the first media to support Ethernet with 10BASE2 and 10BASE5 that transmitted 10 Gb/s up to 185 meters or 500 meters, respectively. The term “coaxial” refers the fact that the cable’s center conductor and shield share the same axis, or center point. Some coaxial cable may include multiple shields, such as a quad shielded coax that includes two layers that each consist of a braided shield over a foil shield. It’s the shielding that makes coaxial cable highly resistant to electromagnetic interference and able to carry high frequency signals over long distances.
同轴电缆布线很长一段时间用来传输数据和视频信号，它也是第一批支持10Base2和10Base5（10Base2 在185m可以数据达到10Gb/s ，10Base5在500m可以达到10Gb/s），“同轴”的意思是电缆的中心导体和屏蔽共用同一轴线或中心点。一些同轴电缆也许包含多层屏蔽，例如：四屏蔽同轴电缆，该同轴电缆包括2层，每一层由箔屏蔽上的编织屏蔽组成。正是这种屏蔽使得同轴电缆具有高度抗电磁干扰的能力，并能够在长距离上传输高频信号。
While we often think of coax as being only deployed in residential applications for broadband video and cable TV (CATV), it can still be found in commercial enterprise environment for everything from closed circuit television (CCTV), audio and video, to radio antenna and even some network connections. It therefore makes sense to understand this cable media and how to test it.
The Primary Types
There are several different types of coax cables to support a wide range of specialty applications, such as satellite communications, industrial, military and marine applications. The three most common non-industrial coax types are RG6, RG11 and RG59, with RG6 being the most common type you will likely encounter in the enterprise for applications like CCTV and CATV. RG11 has a larger center conductor than RG6, which means it has lower insertion loss and can transmit signals further than RG6. However, thicker RG11 cables cost more and are extremely inflexible, making them impractical for deployment in premise applications and better suited for use in longer-run outside plant installations or for straight backbone links. RG59 is more flexible than RG6, but it features even higher loss and is rarely used anymore except in low-bandwidth, low-frequency analog video applications where distances are short and pathway space is limited (think back-up camera in your car).
Coaxial cables also come in various impedances—typically 50, 75 and 93 ohm. 50 ohm coaxial offers higher power handling and is primarily used for radio transmitters like Ham radios, CBs and walkie-talkies. 75 ohm cable does a better job of maintaining signal strength and is primarily used for connecting any type of receiving device such as CATV receivers, high-definition TVs and digital recorders. Originally used in mainframe IBM networks in the 1970s and early 1980s, 93 ohm coax is rare and expensive. While 75 ohm coax is likely the impedance you will encounter in most present-day applications, it’s important to note that all components in a coaxial cabling system should have the same impedance to avoid internal reflections at connection points that can cause signal loss and poor video quality.
Digital Signal 3 (DS3) signals used to carry traffic in central offices (also referred to as a T3 line) also use coaxial cable, including 75 ohm Type 735 and Type 734. Type 735 cable can be used to cover distances up to 69 meters, while Type 734 cable can be used up to 137 meters. RG6 cable may also be used to carry DS3 signals but over shorter distances.
Testing Made Easy
对于任何同轴电缆，安装的成功依赖于使用高品质的元件和正确的安装方法，尤其是连接器的安装。Insertion loss, which is affected by the overall length of the installed link, is the primary parameter that ensures coaxial cabling will support the intended application.
ANSI/TIA-568-4.D specifies requirements for 75 ohm broadband coaxial cabling, cords and connecting hardware to support CATV, satellite television and other broadband applications. For the Cabling Subsystem 1 between the outlet and the first distribution point, the length limit is 46 meters for RG6 and 90 meters for RG11. For a Cabling Subsystem 2 between distribution points, the length limit remains at 46 meters for RG6 and increases to 100 meters for RG11. For each of these deployments, TIA-568-4.D specifies insertion loss limits over the frequency range of 5 to 1002 MHz.
按照ANSI / TIA 568 – 4.D标准75欧姆同轴宽带布线，支持有线电视、卫星电视和其他宽带应用。对于布线子系统，长度限制是46米和90米RG6 RG11为中心。fo布线子系统2点之间的长度分布，限制仍然在46米for RG6 RG11和增加到100米。for each of these deployments，TIA 568 – 4.D指定插入损耗范围为5Mhz至1002Mhz。
Testing is made easy with Fluke Networks’ DSX-CHA003 Coax Adapter for use with DSX CableAnalyzer™ Series Copper Cable Certifiers. With support for RG6 and RG11 coaxial cabling, the DSX-CHA003 Coax Adapter tests to the TIA insertion loss limits over the full frequency range. Because insertion loss is strongly influenced by the length of the installed link whereby a shorter link may pass even when performance has been significantly degraded by cable damage or poorly installed connectors, the DSX CableAnalyzer also provides Length-Scaled test limits that automatically adjust insertion loss limit based on the actual measured length of the cabling segment.
使用Fluke Networks的DSX-CHA003同轴适配器进行测试很容易，该同轴适配器用于DSX电缆分析仪系列铜电缆认证。在RG6和RG11同轴电缆的支持下，DSX-CHA003同轴适配器在全频范围内测试TIA插入损耗极限。因为插入损耗强烈地受到所安装的链路的长度的影响，因此即使由于电缆损坏或连接器安装不良而导致性能显著下降，较短的链路也可能通过，所以DSX CableAnalyzer还提供了长度缩放的测试限制，该测试限制自动进行广告。基于电缆段实际测量长度的插入损耗极限。
The DSX CableAnalyzer also provides Length-Scaled DS-3 test limits for Type 734, Type 735 and RG6 coaxial cabling used in central office applications. And while only encountered in rare lower-speed applications where a distance greater than 100 meters is required, the DSX CableAnalyzer can also test 50 ohm coaxial cabling used to support legacy 10BASE2 or 10BASE5 Ethernet.