當(dāng)談到通纜測(cè)試的時(shí)候，我們大部分都是討論雙絞線的測(cè)試，例如：CAT6，CAT6A和CAT8。盡管這類布線類型已經(jīng)廣泛用于部署語(yǔ)音、數(shù)據(jù)和視頻網(wǎng)絡(luò)傳輸，但這并不意味著你只會(huì)面臨這類布線系統(tǒng)。

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.

同軸電纜布線很長(zhǎng)一段時(shí)間用來(lái)傳輸數(shù)據(jù)和視頻信號(hào)，它也是第一批支持10Base2和10Base5（10Base2 在185m可以數(shù)據(jù)達(dá)到10Gb/s ，10Base5在500m可以達(dá)到10Gb/s），“同軸”的意思是電纜的中心導(dǎo)體和屏蔽共用同一軸線或中心點(diǎn)。一些同軸電纜也許包含多層屏蔽，例如：四屏蔽同軸電纜，該同軸電纜包括2層，每一層由箔屏蔽上的編織屏蔽組成。正是這種屏蔽使得同軸電纜具有高度抗電磁干擾的能力，并能夠在長(zhǎng)距離上傳輸高頻信號(hào)。

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.

雖然我們通常認(rèn)為同軸電纜僅部署在寬帶視頻和有線電視(CATV)的住宅應(yīng)用中，但是它仍然可以在商業(yè)企業(yè)環(huán)境中找到，從閉路電視(CCTV)、音頻和視頻、到無(wú)線電天線甚至一些網(wǎng)絡(luò)連接。因此，理解這種同軸電纜和如何測(cè)試它是有意義的。

The Primary Types

主要類型

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).

有幾種不同類型的同軸電纜，以支持廣泛的專業(yè)應(yīng)用，如衛(wèi)星通信，工業(yè)，軍事和海洋應(yīng)用。最常見的三種非工業(yè)同軸電纜類型是RG6、RG11和RG59，其中RG6是您在企業(yè)中可能遇到的用于CCTV和有線電視等應(yīng)用的最常見類型。RG11具有比RG6大的中心導(dǎo)體，這意味著它具有更低的插入損耗，并且可以比RG6發(fā)送更多的信號(hào)。然而，較厚的RG11電纜成本更高，并且極其不靈活，使得它們不適合部署在房屋應(yīng)用中，并且更適合于在長(zhǎng)時(shí)間運(yùn)行的外部工廠安裝或用于直骨干鏈路。RG59比RG6更靈活，但是它具有更高的損耗，并且除了在低帶寬、低頻的模擬視頻應(yīng)用中（距離很短并且路徑空間有限）之外，很少再使用它（想想你車中的備用攝像機(jī)）。

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.

同軸電纜也有各種阻抗，通常為50, 75歐姆和93歐姆。50歐姆同軸提供更高的功率處理，主要用于無(wú)線電發(fā)射器，如無(wú)線電臺(tái)，廣播和對(duì)講機(jī)。75歐姆電纜在保持信號(hào)強(qiáng)度方面做得更好，主要用于連接任何類型的接收設(shè)備，如有線電視接收機(jī)、高清電視和數(shù)字記錄器。最初在20世紀(jì)70年代和80年代初的大型IBM網(wǎng)絡(luò)中使用，93歐姆同軸電纜是罕見的和昂貴的。雖然75歐姆同軸電纜可能是您在當(dāng)今大多數(shù)應(yīng)用中遇到的阻抗類型，但需要注意的是，同軸電纜系統(tǒng)中的所有組件都應(yīng)該具有相同的阻抗，以避免在連接點(diǎn)處出現(xiàn)內(nèi)部反射，從而可能導(dǎo)致信號(hào)丟失和視頻質(zhì)量下降。

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.

數(shù)字信號(hào)3(DS3)信號(hào)用于在中央辦公室承載業(yè)務(wù)(也稱為T3線路)也使用同軸電纜，包括75歐姆735型和734型。735型電纜可以用來(lái)覆蓋69米的距離，而734型電纜可以使用到137米。RG6電纜也可用于承載DS3信號(hào)，但在更短的距離。

Testing Made Easy

測(cè)試容易

對(duì)于任何同軸電纜，安裝的成功依賴于使用高品質(zhì)的元件和正確的安裝方法，尤其是連接器的安裝。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標(biāo)準(zhǔn)75歐姆同軸寬帶布線，支持有線電視、衛(wèi)星電視和其他寬帶應(yīng)用。對(duì)于布線子系統(tǒng)，長(zhǎng)度限制是46米和90米R(shí)G6 RG11為中心。fo布線子系統(tǒng)2點(diǎn)之間的長(zhǎng)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指定插入損耗范圍為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同軸適配器進(jìn)行測(cè)試很容易，該同軸適配器用于DSX電纜分析儀系列銅電纜認(rèn)證。在RG6和RG11同軸電纜的支持下，DSX-CHA003同軸適配器在全頻范圍內(nèi)測(cè)試TIA插入損耗極限。因?yàn)椴迦霌p耗強(qiáng)烈地受到所安裝的鏈路的長(zhǎng)度的影響，因此即使由于電纜損壞或連接器安裝不良而導(dǎo)致性能顯著下降，較短的鏈路也可能通過，所以DSX CableAnalyzer還提供了長(zhǎng)度縮放的測(cè)試限制，該測(cè)試限制自動(dòng)進(jìn)行廣告。基于電纜段實(shí)際測(cè)量長(zhǎng)度的插入損耗極限。

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.

DSX電纜分析儀還提供了用于中央辦公室應(yīng)用的734型、735型和RG6型同軸電纜的長(zhǎng)度縮放DS-3測(cè)試標(biāo)準(zhǔn)。雖然只在需要大于100米的距離的罕見的低速應(yīng)用中遇到，但是DSX電纜分析儀還可以測(cè)試用于支持傳統(tǒng)10BASE2或10BASE5以太網(wǎng)的50歐姆同軸電纜。

首先，對(duì)同軸電纜的測(cè)試是基于TDR技術(shù)，測(cè)試結(jié)果與性能與同軸電纜的特性阻抗密切相關(guān)；特性阻抗的測(cè)試一般是測(cè)試電纜近似的特性阻抗，并非真正意義上的實(shí)際真有效值，如果在標(biāo)準(zhǔn)規(guī)定的范圍之內(nèi)，即可認(rèn)可是合乎要…

首先，對(duì)同軸電纜的測(cè)試是基于TDR技術(shù)，測(cè)試結(jié)果與性能與同軸電纜的特性阻抗密切相關(guān)；
特性阻抗的測(cè)試一般是測(cè)試電纜近似的特性阻抗，并非真正意義上的實(shí)際真有效值，如果在標(biāo)準(zhǔn)規(guī)定的范圍之內(nèi)，即可認(rèn)可是合乎要求的，如果超過相關(guān)的標(biāo)準(zhǔn)，通過TDR技術(shù)大致可以定位出阻抗異常的點(diǎn)；
同軸電纜的測(cè)試還有一個(gè)重要指標(biāo)電阻。電阻的測(cè)量實(shí)際上測(cè)試的是電力和端接器的環(huán)路電阻，如果末端兵沒有接上端接器或者電纜本身就是開路狀態(tài)，那么電阻值會(huì)變?yōu)闊o(wú)窮大；反之電纜或端接器短路顯示的電阻值近似為0歐姆；當(dāng)測(cè)試的電阻值超過400歐姆，則報(bào)告錯(cuò)誤；
同軸電纜長(zhǎng)度的測(cè)試是應(yīng)該在開路狀態(tài)下進(jìn)行測(cè)試的，并且末端不允許接有端接器；因?yàn)槎私悠鲿?huì)吸收或者消除信號(hào)的反射，所以TDR技術(shù)是無(wú)法測(cè)試出長(zhǎng)度參數(shù) 的，所以只能在未接端機(jī)器的情況下準(zhǔn)確測(cè)試出同軸電纜的長(zhǎng)度。實(shí)際測(cè)試距離基于不同的特性阻抗和線纜半徑，標(biāo)準(zhǔn)中的長(zhǎng)度極限值也設(shè)置各異，下表中截取了部分標(biāo)準(zhǔn)中關(guān)于對(duì)長(zhǎng)度測(cè)量的定義：