请教下近端串扰这个值具体是怎么计算的？...

<p>有这样一句话：近端串扰并不表示在近端点产生的串扰，它只表示在近端所测量到的值，其测量值会岁电缆长度不同而变化 不知道怎么理解？</p><p>既然是近端测量的，那测量的不就是近端的干扰信号量的值吗？跟长度又有什么关系（个人觉得远端串扰才会受长度的影响）？这个值到底是个什么公式计算得到。</p><p>谢谢大家<br/></p>

<p>很专业的知识&nbsp; 高手来解答一下</p><p></p>

<span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">当电流在一条导线中流通时，会产生一定的电磁场，干扰相邻导线上的信号。频率越高这种影响就越大。双绞线就是利用两条导线绞合在一起后，因为相位相差</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">180</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">度的原因而抵消相互间的干扰的。绞距越紧则抵消效果越佳，也就越能支持较高的数据传输速率。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　近端串扰是指在与发送端处于同一边的接收端处所感应到的从发送线对感应过来的串扰信号。在串扰信号过大时，接收器将无法判别信号是远端传送来的微弱信号还是串扰杂讯。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　需要注意的是，表示低</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">时的值越大</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">(</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">如</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">45dB)</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">，发送的信号与串扰信号幅度差就越大，高</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">的值就越小</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">(</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">如</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">20dB)</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">，而这是要设法避免的。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　为了符合</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">5</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">类规格，在电缆端接处的非绞接部分长度不能超过</span><chmetcnv wst="on" tcsc="0" numbertype="1" negative="False" hasspace="False" sourcevalue="13" unitname="米"><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">13</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">米</span></chmetcnv><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">。通常会产生过量</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">的原因有：</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　使用不是绞线的跳线。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　没有按规定压接终端。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　使用老式的</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">66</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">接线块。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　使用非数据级的连接器。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　使用语音级的电缆。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　使用插座对插座的耦合器。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br/><br/></span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">　　另外，要特别注意，在链路两端测量</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">值时，尤其在长度大于</span><chmetcnv wst="on" tcsc="0" numbertype="1" negative="False" hasspace="False" sourcevalue="40" unitname="米"><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">40</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">米</span></chmetcnv><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">时，远端的串扰会被链路的衰减所抵消，而无法在近端测量到其</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">值。在链路两端测量到的</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">值是不一样的，因此所有的测试标准都要求在链路两端测量</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">NEXT</span><span style="FONT-SIZE: 9pt; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">值。</span><span lang="EN-US" style="FONT-SIZE: 9pt; FONT-FAMILY: &quot;Times New Roman&quot;; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><br style="mso-special-character: line-break;"/><br style="mso-special-character: line-break;"/></span>