2.6.7 Crosstalk Issues PDF

2.6.7 Crosstalk Issues Crosstalk usually indicates a problem with bad wiring (poor quality or damaged or the improper type for the application), a bad connector, or improper termination. Check the cable for excessive untwisting at the ends and fo...

2.6.7 Crosstalk Issues Crosstalk usually indicates a problem with bad wiring (poor quality or damaged or the improper type for the application), a bad connector, or improper termination. Check the cable for excessive untwisting at the ends and for kinks or crush points along its run. Crosstalk is also measured in dB, but unlike insertion loss, higher values represent less noise. Again, the expected measurements vary according to the cable category and application. There are various types of crosstalk that can be measured: Near End (NEXT)—This measures crosstalk on the receive pairs at the transmitter end and is usually caused by excessive untwisting of pairs or faulty bonding of shielded elements. Attenuation to Crosstalk Ratio, Near End (ACRN)—This is the difference between insertion loss and NEXT. ACR is equivalent to a signal-to-noise ratio (SNR). A high value means that the signal is stronger than any noise present; a result closer to zero means the link is likely to be subject to high error rates. Attenuation-to-Crosstalk Ratio, Far End (ACRF)—Far-end crosstalk (FEXT) is measured on the receive pairs at the recipient end. The difference between insertion loss and FEXT gives ACRF, which measures cable performance regardless of the actual link length. Power Sum—Gigabit and 10 GbE Ethernet use all four pairs. Power sum crosstalk calculations (PSNEXT, PSACRN, and PSACRF) confirm that a cable is suitable for this type of application. They are measured by energizing three of the four pairs in turn. Alien Crosstalk—This is signal traffic from cables in close proximity that causes interference to a disturbed or victim cable. This is commonly caused by cinching a cable bundle with ties too tightly and by poorly terminated cabling. Complete loss of connectivity indicates a break in the cable (or a completely faulty installation), while intermittent loss of connectivity is more likely to be caused by attenuation, crosstalk, or noise. Copyright © The Computing Technology Industry Association, Inc. All rights reserved.