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隨著當(dāng)今信息傳輸技術(shù)的飛速發(fā)展，布線系統(tǒng)的傳輸速率在穩(wěn)步加快的同時(shí)也帶來了某種防干擾的脆弱性，這是因?yàn)閭鬏斝畔⒌念l率越高，信號(hào)的敏感性增加，同時(shí)它們的能量越來越弱，此時(shí)的布線系統(tǒng)就越容易受干擾。
干擾無處不在
電纜及設(shè)備會(huì)對(duì)其他元件產(chǎn)生干擾或被其他干擾源嚴(yán)重干擾，例如：計(jì)算機(jī)屏幕， 電動(dòng)機(jī)， 移動(dòng)電話， 無線電轉(zhuǎn)播設(shè)備， 數(shù)據(jù)傳輸及動(dòng)力電纜，等等。
潛在的竊聽者，網(wǎng)絡(luò)犯罪及黑客不斷增加，由于他們對(duì)UTP電纜信息傳輸?shù)臄r截會(huì)造成巨大的損害及損失。哪怕沒有物理連接，攔截UTP電纜上傳輸?shù)男畔⒁彩欠浅Ｈ菀椎�，侵入者只需要有一臺(tái)無線接收機(jī)，信號(hào)處理設(shè)備及一臺(tái)便攜機(jī)即可工作。數(shù)據(jù)攔截在幾厘米至幾百米的范圍內(nèi)都有可能發(fā)生，并且在大多數(shù)情況下完全無法監(jiān)測(cè)。尤其在使用高速數(shù)據(jù)網(wǎng)絡(luò)時(shí)，攔截大量信息所需要的時(shí)間顯著低于攔截低速數(shù)據(jù)傳輸所需要的時(shí)間。
數(shù)據(jù)雙絞線中的絞合線對(duì)在低頻下可以靠自身的絞合來抵抗外來干擾及線對(duì)之間的串音，但在高頻情況下（尤其在頻率超過250Mhz以上時(shí)），僅靠線對(duì)絞合已無法達(dá)到抗干擾的目的，只有屏蔽才能夠抵抗外界干擾。
電纜屏蔽層的作用就象一個(gè)法拉第護(hù)罩，干擾信號(hào)會(huì)進(jìn)入到屏蔽層里，但卻進(jìn)入不到導(dǎo)體中。因此，數(shù)據(jù)傳輸可以無故障運(yùn)行。
由于屏蔽電纜 (STP) 比非屏蔽電纜具有較低的輻射散發(fā)，因而防止了網(wǎng)絡(luò)被攔截。屏蔽網(wǎng)絡(luò)(屏蔽的電纜及元器件)能夠顯著減小進(jìn)入到周圍環(huán)境中而可能被攔截的電磁能輻射等級(jí)。
百通憑借多年在數(shù)據(jù)傳輸及音視頻領(lǐng)域的專業(yè)應(yīng)用，開發(fā)了一系列獨(dú)有的屏蔽方式，以提高電纜抵抗電磁干擾/射頻干擾的能力，確保了信號(hào)的完整性，為數(shù)據(jù)，音頻和視頻的順利傳輸提供了保證，并避免了故障時(shí)間。百通的屏蔽電纜已在各個(gè)領(lǐng)域應(yīng)用多年，所以我們?cè)诟叨葘I(yè)化的電子領(lǐng)域內(nèi)所積累的用于數(shù)據(jù)傳輸?shù)慕?jīng)驗(yàn)具有無可比擬的價(jià)值。對(duì)于特殊的干擾問題，可以要求百通為客戶專門設(shè)計(jì)和制造屏蔽電纜方案。
新型的屏蔽方案
“French Braid”屏蔽
百通的專利產(chǎn)品“French Braid”是一 種雙螺旋形(雙層裸銅線屏蔽)屏蔽，而將兩個(gè)螺旋在一點(diǎn)織連在一起。與傳統(tǒng)網(wǎng)狀屏蔽相比，該產(chǎn)品提高了柔韌性，這種構(gòu)造比標(biāo)準(zhǔn)的螺旋屏蔽提高了抗撓壽命，并比螺旋屏蔽或傳統(tǒng)的網(wǎng)狀屏蔽降低了顫噪或靜電噪聲�！癋rench Braid”比標(biāo)準(zhǔn)的網(wǎng)狀屏蔽容易端接，因?yàn)樗鼪]有完全織連在一起。它比單螺旋編織屏蔽的DC(直流電)環(huán)路阻抗要低，性能更好�！癋rench Braid” 特性在百通新型“Flexnake”蛇型電纜中表現(xiàn)的更為顯著。
網(wǎng)狀屏蔽
網(wǎng)狀屏蔽在保持良好的柔韌性及抗撓壽命的同時(shí)，提供了超群的結(jié)構(gòu)整體性。這些屏蔽對(duì)于降低低頻干擾是理想的選擇，比起箔層屏蔽來說，降低了直流阻抗。網(wǎng)狀屏蔽在音頻以及射頻范圍非常有效。通常，網(wǎng)狀屏蔽覆蓋率越高，屏蔽效果就越好。
箔層屏蔽
箔層屏蔽是由聚脂或聚丙烯薄膜上附著一層鋁箔形成。這層薄膜給屏蔽提供了機(jī)械強(qiáng)度及良好的絕緣性能。箔層屏蔽可100％覆蓋電纜。由于它們的體積小，箔層屏蔽通常用于多對(duì)數(shù)電纜的單線對(duì)屏蔽以減少相互的串?dāng)_。箔層屏蔽重量輕、體積小，比網(wǎng)狀屏蔽造價(jià)低，在射頻范圍內(nèi)通常更加有效。箔層屏蔽比起網(wǎng)狀屏蔽的柔韌性更好，但抗撓壽命較短。與箔層屏蔽一起使用的接地線，使端接更加容易，并將靜電釋放入大地。
百通使用了短接工藝來保持金屬與金屬的接觸，以獲得高頻性能的改善。沒有短接就會(huì)出現(xiàn)信號(hào)泄漏的狹縫。
為了改進(jìn)傳統(tǒng)的短接方式，百通使用了旨在多對(duì)電纜應(yīng)用和減少串?dāng)_的Z－Fold技術(shù)。此技術(shù)包括了絕緣折迭及短接折迭。短接折迭提供了金屬與金屬之間的接觸，而絕緣折迭防止了多線對(duì)纜單對(duì)屏蔽間的相互短路。Z－Fold的設(shè)計(jì)增加了高頻段箔層屏蔽的有效范圍。
箔層的設(shè)計(jì)
作為屏蔽技術(shù)的創(chuàng)新者，百通開發(fā)了幾種專有的屏蔽設(shè)計(jì)方案。百通是第一家開發(fā)以鋁/聚脂箔層作為電纜屏蔽的公司，并被授予“Beldfoil”屏蔽專利。Beldfoil屏蔽首先做到了100％的電纜覆蓋，增強(qiáng)抵抗了音頻及無線頻率的輻射及侵入。
箔層屏蔽一般是在導(dǎo)體絕緣層上粘合一層附著物。粘合的優(yōu)點(diǎn)在于進(jìn)行更加快捷、方便及可靠地端接。此外，粘合還能防止屏蔽層下的水分發(fā)生擴(kuò)散。如果電纜護(hù)套破損，粘合的屏蔽還能幫助保護(hù)電纜絕緣層免受污染。百通將這些優(yōu)點(diǎn)都融合在“Duobond? II”屏蔽之中。
組合屏蔽
組合屏蔽包括多層屏蔽。它們能夠在整個(gè)頻譜提供最大的屏蔽效果。箔層/網(wǎng)狀屏蔽結(jié)合了箔層屏蔽100％的覆蓋范圍與網(wǎng)狀屏蔽的機(jī)械強(qiáng)度和低直流阻抗等優(yōu)點(diǎn)。其他現(xiàn)有的組合屏蔽包括各種箔層/網(wǎng)狀/箔層設(shè)計(jì)、網(wǎng)狀/網(wǎng)狀或網(wǎng)狀/螺旋設(shè)計(jì)等。
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Belden？ Cable - Reliable Performance in Broadcasting Environments
Innovating Shielding Solutions
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Braid Shields
Braid shields provide superior structural integrity while maintaining good flexibility and flex life. These shields are ideal for minimizing low frequency interference and have lower DC resistance than foil. Braid shields are effective at audio, as well as RF ranges. Generally, the higher the braid coverage, the more effective the shield.
Foil Shields
Foil shields consist of aluminum foil laminated to a polyester or polypropylene film. The film gives the shield mechanical strength and bonus insulation. Foil shields provide 100% cable coverage. Because of their small size, foil shields are commonly used to shield individual pairs of multi-pair cables to reduce crosstalk. They have less weight, bulk, and cost less than braid shields and are generally more effective in RF ranges. Foil shields are more flexible than braid but have a shorter flex life. Drain wires are used with foil shields to make termination easier and to ground electrostatic discharges.
Belden uses a shorting fold technique to maintain metal-to-metal contact for improved high frequency performance. Without the shorting fold, a slot is created through which signals can leak.
Belden improves on the traditional shorting fold by employing the Z-Fold？ designed for use in multi-pair applications to reduce crosstalk. The Z-Fold combines an isolation fold and a shorting fold. The shorting fold provides metal-to-metal contact while the isolation fold keeps shields from shorting to one another in multi-pair, individually shielded cables. The Z-Fold design increases the foil shield's range of effectiveness to higher frequencies.
Foil Tape Designs
As an innovator in shielding technology, Belden has developed several shields of exclusive design. Belden was the first to develop the aluminum/polyester foil used as a cable shield and was awarded a patent for the Beldfoil？ shield. The Beldfoil shield was the first to offer 100% cable coverage, improving protection against radiated emission and ingress at audio and radio frequencies.
Foil shields may be bonded to a conductor's insulation with a layer of adhesive. The advantages of bonding include faster, easier, and more reliable termination. In addition, bonding prevents moisture from wicking under the shield. Should the cable jacket rupture, the bonded shield helps protect the cable's insulation against contamination. Belden combines these assets in the Duobond？ II shield.
Combination Shields
Combination shields consist of more than one layer of shielding. They provide maximum shield efficiency across the frequency spectrum. The combination foil/braid shield combines the advantages of 100% foil coverage, plus the strength and low DC resistance of a braid. Other combination shields available include various foil/braid/foil designs, braid/braid, or foil/spiral.
Special Noise/lnterference Problems in Broadcasting
Triboelectric noise is generated by mechanical motion of a cable, causing movement in the cable's shield. Belden detects and measures triboelectric noise through the use of our own Low Noise Test equipment. The test procedure and equipment have been developed from a combination of three low noise standards--NBS, ISA-S, and MIL-C-17.
Mechanically induced noise is a critical and frequent concern in the use of guitar cords and microphone cables. Generally, test readings should be below 150 millivolts for low impedance microphone cables and below 15 millivolts for guitar cords. The properties of special conductive tapes and insulations are employed at Belden to prevent mechanically induced noise. Consult with Belden Technical Support Department for the proper cable construction needed to combat the noise problems associated with your application.
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好文章，要是在有圖片就更好了。
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謝謝，樓主。長(zhǎng)見識(shí)了。附件為什么打不開啊
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