IDEAL INDUSTRIES FIBERTEK, Руководство пользователя

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Chapter 3
Structured Cable Field Calibration and Testing
3-25
Power Sum NEXT and Power Sum ELFEXT
Power Sum tests measure the crosstalk effects of three transmitting pairs on the
fourth pair in the same cable sheath.
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Effects of
3 Pairs on 1 Pair
During the Power Sum NEXT test, six measurements are made at each end of the
cable and combined (pairs 1-2, 3-6, and 4-5 vs. pair 7-8, etc.) for a total of eight
measurements.
Figure 3-14: Power Sum NEXT Test Screen
During the Power Sum ELFEXT test, twelve measurements are made at the DH side of
the cable and combined (pairs 1-2, 3-6, 4-5 vs. pair 7-8, etc.) for a total of four
measurements.
Figure 3-15: Power Sum ELFEXT Test Screen
Note: Power Sum NEXT measurements will generally read 2 - 3 dB lower in value
(higher crosstalk) than conventional NEXT.
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