Information Technology Reference
In-Depth Information
TABLE 15.1
Connecting Hardware Attenuation and NEXT Limits of TIA-568-C
Connecting hardware limits (loss in dB)
Attenuation
NEXT loss
Category
Frequency, MHz 3 5 5e 3 5 5e
1.0 0.4 0.1 0.1 58.1 65.0 65.0
4.0 0.4 0.1 0.1 46.0 65.0 65.0
8.0 0.4 0.1 0.1 40.0 62.0 64.9
10.0 0.4 0.1 0.1 38.1 60.0 63.0
16.0 0.4 0.2 0.2 34.0 56.0 58.9
20.0 0.2 0.2 54.0 57.1
25.0 0.2 0.2 52.1 55.0
31.25 0.2 0.2 50.2 53.1
62.5 0.3 0.3 44.2 47.1
100.0 0.4 0.4 40.1 43.0
NOTE: The maximum attenuation values shown are specified at each frequency. Acceptable values of attenuation
are a lesser (or equal) dB value than shown in the table. The NEXT loss shown is calculated from the formula in
TIA-568-C. The formula is based on assumed minimum values at 16 MHz of 34 and 56 dB for Category 3 and 5,
respectively. Acceptable values of NEXT loss are a greater (or equal) dB value than shown in the table, or calcu-
lated from the formula, at a given frequency.
a connector, compared to 9.2 ohms per 100 m for the cable. However, the NEXT
contribution from the connectors can be significant. For example, at 100 MHz, the
NEXT loss of the connecting hardware must be better than 43.0 dB, while the cable
alone must be better than 32.3 dB for a 100 m length. The entire terminated and
installed Permanent Link allows only an additional 3 dB (to 29.3 dB at 100 MHz)
over the raw cable for all the intervening connecting hardware and installation anom-
alies. This is an area, by the way, where a higher “enhanced” grade cable can increase
the margin of performance of a link. However, the connectors cannot be much
improved and remain compatible with the standard modular design.
The low NEXT requirements of Category 5e and 6 are one of the primary rea-
sons that the traditional screw-type wire terminals are not acceptable in those appli-
cations. You can easily observe the increased NEXT of screw-terminal jacks with
any of the more sophisticated cable scanners. (An increase in NEXT is a lower dB
number, as the measure indicates how low the crosstalk signal is with respect to a
transmitted signal on another pair.)
You might think of the NEXT loss number as the amount of isolation from an
interfering signal. (A higher number is better.) Connector assemblies that are
designed for the higher categories normally use an integral printed circuit board
with carefully routed wiring to minimize NEXT.
