Copyright Goodheart-Willcox Co., Inc. 57 Chapter 2 Network Media—Copper-Core Cable Input signal NEXT Measurement Crosstalk signal Figure 2-9 Near-end crosstalk (NEXT) is a measurement of crosstalk taken at the near end, or input end, of a cable. Goodheart-Willcox Publisher Input signal FEXT Measurement Crosstalk signal Figure 2-10 Far-end crosstalk (FEXT) is a measurement of crosstalk taken at the far end, or output end, of the cable. Goodheart-Willcox Publisher a 100-meter length of cable has a FEXT measurement of 45 dB with an attenuation measurement of 15 dB, the ELFEXT is calculated to be 30 dB. ELFEXT negates much of the attenuation by raising the attenuated signal by a value equal to the attenua- tion. Th is brings the attenuated signal back to the desired level. Th is is what the term ELFEXT implies by “equal level.” It equalizes the loss with a gain. Alien Crosstalk (AXT) Alien crosstalk (AXT) is a measurement of noise introduced outside the cable jack- et, typically caused by other network cables in close proximity. Th is measurement was fi rst introduced in February 2008 as part of the Category 6a standard because of the high-frequency capabilities of this cable. Cables that carry high-frequency signals are susceptible to AXT. At lower frequencies, AXT is not a problem. Copper-Core Cables Copper-core cables are commonly constructed of a center core of copper surround- ed by an insulating jacket. All copper-core cables have an AWG rating. An AWG rating describes the size of a conductor’s diameter. Th e abbreviation AWG rep- resents American Wire Gauge, which is the accepted standard for specifying the size of a conductor. Th e size of a conductor is expressed as a numeric value such as 22, 20, or 18. Th e smaller the number, the larger the diameter of the wire. Figure 2-11 shows a wire gauge. A wire gauge is used to determine the AWG rat- ing or the size of a conductor. Notice that the largest wire measurement on the gauge 2.1, 2.5 NET