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For twisted pair, users are most concerned about several indicators that characterize its performance. These indicators include attenuation, near-end crosstalk, impedance characteristics, distributed capacitance, DC resistance, etc.
(1) Attenuation
Attenuation is a measure of signal loss along a link. Attenuation is related to the length of the cable, and as the length increases, the signal attenuation also increases. Attenuating" db" A unit that represents the ratio of the strength of the signal from the transmitting end of the source to the signal from the receiving end. Since attenuation varies with frequency, it should be measured at all frequencies within the application range.
(2) Near-end crosstalk
Crosstalk is divided into near-end crosstalk and far-end crosstalk (FEXT), the tester mainly measures NEXT, due to the presence of line loss, so the FEXT magnitude has less influence. Near-end crosstalk (NEXT) loss is a measure of signal coupling from one pair of lines to another in a UTP link. For UTP links,NEXT is a key performance metric and one of the most difficult to measure accurately. As the frequency of the signal increases, its measurement difficulty will increase.
NEXT does not represent the crosstalk value generated at the near endpoint, it only represents the crosstalk value measured at the near endpoint. This quantity will vary with the length of the cable, and the longer the cable, the smaller the value. At the same time, the signal at the sending end will also be attenuated, and the crosstalk to other line pairs will be relatively small. Experiments have shown that only the NEXT measured within 40 meters is more realistic.
If the other end is an information socket farther than 40 meters, then it will produce a certain level of crosstalk, but the tester may not be able to measure this crosstalk value. Therefore, it is best to take the NEXT measurement at both endpoints. Today's testers are equipped with corresponding equipment, so that the NEXT value of both ends can be measured at one end of the link.
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