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Near-end crosstalk of Twisted Cable

2021-10-13

Crosstalk is divided into near-end crosstalk and far-end crosstalk (FEXT). The tester mainly measures NEXT. Because of the line loss, the magnitude of FEXT has less influence. Near-end crosstalk (NEXT) loss is the measurement of signal coupling from one pair of wires to another in an unshielded twisted pair link. For unshielded Twisted Cable links, NEXT is a key performance index, and it is also the most difficult index to accurately measure. As the signal frequency increases, its measurement difficulty will increase. NEXT does not mean the crosstalk value generated at the near end point, it just means the crosstalk value measured at the near end point. This value will vary with the length of the cable, the longer the cable, the smaller its value becomes. At the same time, the signal at the transmitting end will be attenuated, and the crosstalk to other wire pairs will be relatively small. Experiments have proved that only the NEXT measured within 40 meters is more real. If the other end is an information socket farther than 40 meters, then it will produce a certain degree of crosstalk, but the tester may not be able to measure this crosstalk value. Therefore, it is best to perform NEXT measurements at both endpoints. Most testers are equipped with corresponding equipment so that the NEXT value at both ends can be measured at one end of the link.