Basic Cabling Testing
FEXT and ELFEXT
7
7-13
In cable, the inductive crosstalk component is very low. Most of the crosstalk is
due to the capacitive component. Because the difference between the two
components is nearly equal to the capacitive component, NEXT and FEXT are
nearly the same in a cable.
Because of how FEXT signals add up along a cable link, good ELFEXT
performance is critical for systems that transmit data over multiple wire pairs.
Examples of these systems are 100BASE-T4, 100VG-AnyLAN, and 1000BASE-T
(Gigabit Ethernet).
NEXT signal B travels farther than A
Signal
source
A
B
Resulting
NEXT
FEXT signals C and D travel the same distance
(the length of the cable)
Signal
source
C
D
Resulting
FEXT
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Figure 7-9. How FEXT Signals are All Equally Attenuated
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