電線電纜網(wǎng) > 數(shù)據(jù) 高頻線纜 > 為什么數(shù)據(jù)纜的特性阻抗標(biāo)稱(chēng)值是100？（完整版）
為什么數(shù)據(jù)纜的特性阻抗標(biāo)稱(chēng)值是100？ - 無(wú)圖版
guodong --- 2008-01-22 10:37:46
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在IEC61156和YD1019都數(shù)據(jù)纜的特性阻抗的標(biāo)稱(chēng)值規(guī)定在100±5歐
有誰(shuí)知道為什么標(biāo)稱(chēng)值是100？如果過(guò)大對(duì)電纜性能有生命影響?如果過(guò)小對(duì)電纜性能有什么影響？
qinys --- 2008-01-22 11:16:50
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有點(diǎn)難度
ok509 --- 2008-01-22 11:32:32
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在這里給你提供一個(gè)想問(wèn)題的思路!
一次參數(shù)和二次參數(shù)都是相互關(guān)聯(lián)的,
不能孤立的去看,去想特性阻抗為什么是100歐姆.
特性阻抗為100歐姆的時(shí)候其他傳輸參數(shù)才能獲得最優(yōu)值,更有利于傳輸性能.
money --- 2008-01-22 11:53:33
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CABLE得阻抗有50 / 75 / 100 ohms
rudy2014 --- 2008-01-22 22:00:18
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風(fēng)雨123 --- 2008-01-23 08:48:00
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leopan --- 2008-01-23 09:18:58
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拙見(jiàn)，有不對(duì)的地方請(qǐng)多包涵！
特性阻抗是根據(jù)實(shí)際情況確定的一個(gè)額定數(shù)值，在確定特性阻抗的時(shí)候要考慮多方面的因數(shù)：
1.傳輸功率,距離與傳輸條件
比如網(wǎng)絡(luò)線,水晶頭的插孔就決定了線的絕緣外徑應(yīng)該在0.9-1.05之間(近似),太大太小都對(duì)裝配有影響.當(dāng)絕緣外徑確定了后,然后需要驗(yàn)證的是傳輸?shù)墓β?如果傳輸功率達(dá)不到,當(dāng)然就行把導(dǎo)體截面加大了,到時(shí)水晶頭都得改了.想一下,水晶頭要是有拳頭那么大那是什么效果,呵呵.再下一步就是考慮傳輸?shù)木嚯x了,要傳輸遠(yuǎn)點(diǎn)衰減就得小點(diǎn),截面就得大點(diǎn).導(dǎo)體電阻就得小點(diǎn).當(dāng)然,如果局域網(wǎng)100米就夠了,就不用那么大那么好的導(dǎo)體了.還有,這些沒(méi)有先后的,你當(dāng)然可以先確定功率再算外徑的了.
2.適配問(wèn)題
比如同軸電纜,接線端子是75OHM的,如果你用100OHM的同軸線,阻抗就不匹配了,翻翻那年代的物理都有了,傳輸有功功率是在阻抗匹配的情況下達(dá)到最大.
3.結(jié)構(gòu)尺寸,材料及經(jīng)濟(jì)性
假如根據(jù)傳輸功率,傳輸距離確定了導(dǎo)體的直徑是0.5mm的銅,然后就要確定絕緣材料,絕緣材料理論上當(dāng)然是介電常數(shù)越小越好了,但是要太小了你就做不出來(lái)了,因?yàn)橐_(dá)到規(guī)定的特性阻抗值,絕緣厚度就小得一蹋糊涂了.當(dāng)然要是可能的話(huà),可以把特性阻抗規(guī)定得大點(diǎn).不過(guò)設(shè)計(jì)電纜是要考慮經(jīng)濟(jì)性的,也就是說(shuō)在滿(mǎn)足使用的情況下,盡量省錢(qián),這些都做到了,特性阻抗就出來(lái)了.
另外后面那個(gè)公差值,是根據(jù)傳輸?shù)男Ч驮O(shè)備的加工能力確定的.如果公差太大了,傳輸不穩(wěn)定了,誤碼率高了.掉包多了就麻煩了,公差小了,可能你的導(dǎo)體外徑或者絕緣公差就只能控制在0.000001mm了,那是你不可能做到的.包括進(jìn)口的機(jī)器.
不知道IEC是咋確定的,也不知道說(shuō)對(duì)了沒(méi)有,呵呵.
guodong --- 2008-01-23 09:57:55
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謝謝給位回答！我知道特性阻抗和R、L、C、W有關(guān)系，但是還是不太清楚特性阻抗100是怎么確定的
余澤平 --- 2008-01-23 12:34:29
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根據(jù)電氣性測(cè)試發(fā)現(xiàn)
最大功率處理能力在 線材30 ohms時(shí)
最小信號(hào)衰減能力在 線材77 ohms時(shí)
50 ohms是“歉容”的最佳選擇
既可降低衰減又可處理高功率信號(hào)
因此大部分高頻微波系統(tǒng)選擇 50 ohms
而HDMI/DVI 等是采用雙線差分傳輸
故將特性阻抗標(biāo)準(zhǔn)值定為 100 ohms
阻抗過(guò)大過(guò)小最直接體現(xiàn)的是阻抗匹配導(dǎo)致return loss增大
從而影響產(chǎn)品的傳輸性能
ok509 --- 2008-01-23 15:09:03
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樓上這個(gè)理論我強(qiáng)烈支持!能再清楚點(diǎn)就好了.
leopan --- 2008-01-23 19:14:34
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這個(gè)可能有點(diǎn)用：<轉(zhuǎn)>
<DIV>The History Of 50 ohmsA lot of people ask, so here's the answer to the eternal question, "How did 50 ohms get to be the standard RF transmission line impedance?" Here are a few stories. Bird Electronics will send you a printed copy of their version if you ask for it. This from Harmon Banning of W.L. Gore & Associates, Inc. cable:There are probably lots of stories about how 50 Ohms came to be. The one I am most familiar goes like this. In the early days of microwaves - around World War II, impedances were chosen depending on the application. For maximum power handling, somewhere between 30 and 44 Ohms was used. On the other hand, lowest attenuation for an air filled line was around 93 Ohms. In those days, there were no flexible cables, at least for higher frequencies, only rigid tubes with air dielectric. Semi-rigid cable came about in the early 50's, while real microwave flex cable was approximately 10 years later.Somewhere along the way it was decided to standardize on a given impedance so that economy and convenience could be brought into the equation. In the US, 50 Ohms was chosen as a compromise. There was a group known as JAN, which stood for Joint Army and Navy who took on these matters. They later became DESC, for Defense Electronic Supply Center, where the MIL specs evolved. Europe chose 60 Ohms. In reality, in the US, since most of the "tubes" were actually existing materials consisting of standard rods and water pipes, 51.5 Ohms was quite common. It was amazing to see and use adapter/converters to go from 50 to 51.5 Ohms. Eventually, 50 won out, and special tubing was created (or maybe the plumbers allowed their pipes to change dimension slightly).Further along, the Europeans were forced to change because of the influence of companies such as Hewlett-Packard which dominated the world scene. 75 Ohms is the telecommunications standard, because in a dielectric filled line, somewhere around 77 Ohms gives the lowest loss. (Cable TV) 93 Ohms is still used for short runs such as the connection between computers and their monitors because of low capacitance per foot which would reduce the loading on circuits and allow longer cable runs.Volume 9 of the MIT Rad Lab Series has some greater details of this for those interested. It has been reprinted by Artech House and is available.</DIV>
guodong --- 2008-01-25 13:33:06
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十樓做的解釋很好��！
特性阻抗增大對(duì)數(shù)字通信電纜的各種傳輸特性都有影響，影響嚴(yán)重的就應(yīng)該是回波阻抗。
ok509 --- 2008-01-25 14:57:23
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guodong:
十樓做的解釋很好啊！
特性阻抗增大對(duì)數(shù)字通信電纜的各種傳輸特性都有影響，影響嚴(yán)重的就應(yīng)該是回波阻抗。
兄弟你說(shuō)的不對(duì)!
[/blockquote.
ok509 --- 2008-01-25 15:05:07
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12樓的斑竹給了答案!
1.gives the lowest loss.
2.reduce the loading on circuits and allow longer cable runs
所以這個(gè)阻抗啊,是有點(diǎn)來(lái)歷的.呵呵
guodong --- 2008-01-26 08:30:43
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樓上的師兄好啊！
剛畢業(yè)出來(lái)，很多地方不懂，錯(cuò)的地方還望多多指教。
zhengliang --- 2008-02-10 17:29:11
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最關(guān)鍵就是為了達(dá)到阻抗匹配問(wèn)題
yuza521 --- 2008-02-16 15:19:20
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ok509 --- 2008-02-16 16:47:42
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樓主的問(wèn)題是為什么要設(shè)計(jì)成50，75，100？
心雨 --- 2008-04-04 18:46:56
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數(shù)據(jù)纜的特性阻抗的標(biāo)稱(chēng)值規(guī)定在100±5歐?
應(yīng)該是100±15歐 吧？
AbelGuo --- 2008-04-04 20:23:28
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阻抗全都是 為了信號(hào)的匹配。 阻抗的 不同你要說(shuō)會(huì)有什么樣的后果只可以告訴你后果就是信號(hào)無(wú)法接收或失真。。。
真情 --- 2008-04-05 20:57:53
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樓主可能還不能正確理解阻抗的真正意義,關(guān)于阻抗為何選在100OHM,樓上有為朋友解釋的很詳細(xì),這就和同軸電纜怎么選在50OHM和75OHM一樣,
hrbdgxy --- 2008-04-06 22:44:51
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特性阻抗 是指在線路與終端匹配的情況下,線材所具有的一個(gè)參數(shù)值是與一次參數(shù)(R,L,C,G)有關(guān)的二次參數(shù),通常我們測(cè)試獲得的特性阻抗
其實(shí)是CABLE 的輸入阻抗
liutiefeng --- 2008-04-08 16:36:10
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到底是一個(gè)什麼樣的關(guān)係
guodong --- 2008-09-13 22:18:05
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近日又看了好多資料，對(duì)這個(gè)問(wèn)題又有了更進(jìn)一步的理解．
特性阻抗的設(shè)定主要是為了滿(mǎn)足輸入，輸出設(shè)備和線才之間的阻抗匹配問(wèn)題．
對(duì)特性阻抗影響比較嚴(yán)重的是電容值，它的變化直接影響阻抗的大小
在其他條件不變的條件下，電纜芯線的外徑是控制的電容大小的主要因素
因此在高頻電纜的生產(chǎn)中，芯線的控制就由為重要，設(shè)備優(yōu)秀的企業(yè)可以把同心度做到９７％以上
rats --- 2008-09-17 13:23:45
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根據(jù)理論計(jì)算，其實(shí)比較好的匹配并不是整數(shù)，譬如50歐姆最佳可能是47歐姆。從線路設(shè)計(jì)（如連接匹配等），還有工業(yè)標(biāo)準(zhǔn)化，阻抗采取50，75和100歐姆，這樣整個(gè)轉(zhuǎn)換和匹配比較方便。（2個(gè)50歐并聯(lián)為25歐，2個(gè)串聯(lián)為100歐，看看我們所用的測(cè)試設(shè)備，原始匹配基本上是50歐的）
guodong --- 2008-09-28 19:12:18
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有道理!看來(lái)還要進(jìn)一步學(xué)習(xí)
kaka2004 --- 2008-10-08 08:17:23
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數(shù)據(jù)纜都應(yīng)該是50歐單線，設(shè)計(jì)的時(shí)候也只能用50歐來(lái)計(jì)算，這個(gè)是我們培訓(xùn)時(shí)老師說(shuō)的，還可以通過(guò)C值來(lái)計(jì)算阻抗。
guodong --- 2008-10-12 15:01:16
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呵呵...對(duì)于這個(gè)還沒(méi)有什么了解!
你的培訓(xùn)老師看來(lái)是高手了!
hrbdgxy --- 2008-10-12 20:19:44
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原因很簡(jiǎn)單,終端匹配原則,負(fù)載(輸出阻抗)阻抗是100歐,那么線材必須要求是100
gyc2008 --- 2008-10-13 11:34:41
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解答的很精，學(xué)習(xí)對(duì)我很有幫助。
sxt0533 --- 2008-11-03 10:25:43
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jswjyzw --- 2012-07-03 14:32:54
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chenduo --- 2012-07-20 21:09:42
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zyt088 --- 2012-08-17 15:59:22
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學(xué)習(xí)！
dedyqi --- 2012-08-22 15:23:09
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太牛了，還是不明白
李小龍 --- 2012-08-23 10:26:21
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根據(jù)電氣性測(cè)試發(fā)現(xiàn)
最大功率處理能力在 線材30 ohms時(shí)
最小信號(hào)衰減能力在 線材77 ohms時(shí)
50 ohms是“歉容”的最佳選擇
既可降低衰減又可處理高功率信號(hào)
因此大部分高頻微波系統(tǒng)選擇 50 ohms
而HDMI/DVI 等是采用雙線差分傳輸
故將特性阻抗標(biāo)準(zhǔn)值定為 100 ohms
阻抗過(guò)大過(guò)小最直接體現(xiàn)的是阻抗匹配導(dǎo)致return loss增大
從而影響產(chǎn)品的傳輸性能
余老大的分析已經(jīng)是很給力了，我就借余老大的言論詳細(xì)點(diǎn)說(shuō)一下：
當(dāng)同軸電纜的特性阻抗為７７Ω時(shí)，單位長(zhǎng)度的損耗最低；
當(dāng)同軸電纜的特性阻抗為３０Ω時(shí)，其承受的功率最大。
為了兼顧最小的損耗和最大的功率容量，應(yīng)該在７７Ω和３０Ω之間找一個(gè)適當(dāng)?shù)臄?shù)值。二者的算術(shù)平均值為５３．５Ω，而幾何平均值為４８．０６Ω；
選�。担�Ω的特性阻抗可以做到二者兼顧。
FQC --- 2012-10-24 11:37:29
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h20050967 --- 2012-10-25 08:55:22
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dedyqi --- 2012-11-01 15:59:34
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學(xué)習(xí)了