<p>正好，也有个帖子想一起讨论一下这个话题。</p><p>关于非屏蔽和屏蔽系统，提供一个背景噪音测试的功能，这个功能可以测试线缆所处的位置空间的实际信号强度。</p><p>通过捕捉四周信号的强弱，可以判断铜缆布线的外界环境干扰情况。及时排除动力系统等干扰。</p><p> </p><p></p><p>External Noise Measurements with WireScope Pro<br/>Agilent Technologies WireScope Pro includes the external noise measurement<br/>capability as part of its Alien Crosstalk Toolkit. This tool can be used to<br/>display and store external noise measurement data. External noise testing is<br/>performed continuously on a selected cable pair or other devices under test,<br/>with a refresh rate for each sweep of less than 3 seconds. With a maximum<br/>hold plot, it can capture the worst case measured external noise spikes over<br/>long periods of time.<br/>The IEEE Std 802.3an™-2006 standard (section 55.5.4.4) for port type<br/>10GBASE-T defines a receiver alien crosstalk noise tolerance of -141.9<br/>dBm/Hz (-81.9 dBm/MHz). Measurements are compared to the 10GBASE-T<br/>limits for quick assessment of possible impact on performance. Figure 2<br/>illustrates the noise measurement screen on the WireScope Pro with<br/>1000BASE-T network traffic on an adjacent cable relative to the 10GBASE-T<br/>alien crosstalk noise tolerance limit.</p><p>Advantages of Direct Noise Measurements<br/>Making direct noise measurements of a cabling link have a number of distinct advantages.<br/>• If the network is already operational, it is difficult, and at times impossible, to bring down network<br/>links for the purpose of performing alien crosstalk tests. Direct noise measurements allows the<br/>alien crosstalk caused by actual network traffic to be measured, as opposed to the alien crosstalk<br/>performance measurements using the field tester transmit signal.<br/>• It measures without producing any test signals, eliminating the unwanted crosstalk into adjacent<br/>‘live’ network links.<br/>• In some cases, RF noise in the environment, produced by sources other than alien crosstalk from<br/>adjacent links, may cause network performance degradation. This external noise measurement tool<br/>includes the effects from such contributors.<br/>• The external noise measurements can be performed over long periods of time; enabling the<br/>detection of sporadic surges in RF noise that can cause degradation in network performance.</p>
[此贴子已经被作者于2007-10-15 13:10:55编辑过]
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