Information Technology Reference
In-Depth Information
TABLE 15.2
Cable Attenuation and NEXT Limits of TIA-568-C
Horizontal and backbone cable limits (loss in dB)
Attenuation
NEXT loss
Category
Frequency, MHz
3
5
5e
3
5
5e
0.064
0.6
0.7
0.7
0.150
52.7
74.7
77.7
0.256 1.2 1.1 1.1
0.512 1.8 1.5 1.5
0.772 2.2 1.8 1.8 43.0 64.0 67.0
1.0 2.6 2.0 2.0 41.3 62.3 65.3
4.0 5.6 4.1 4.1 32.3 53.3 56.3
8.0 8.5 5.8 5.8 27.8 48.8 51.8
10.0 9.7 6.5 6.5 26.8 47.3 50.3
16.0 13.1 8.2 8.2 23.3 44.3 47.2
20.0 9.3 9.3 42.8 45.8
25.0 10.4 10.4 41.3 44.3
31.25 11.7 11.7 39.9 42.9
62.5 17.7 17.0 35.4 37.2
100.0 22.0 22.0 32.3 35.3
NOTE: The maximum attenuation values shown are calculated from the formula in TIA-568-C. The attenuation
value is per 100 m (238 ft) at 20°C. An increase of 0.4% per degree Celsius is added to the value shown for
Category 5 and 5e cables. Acceptable values of attenuation are a lesser (or equal) dB value than shown in the
table. Values for frequencies below 0.772 MHz are shown for reference only and are not required for testing.
The NEXT loss shown is calculated from the formula in TIA-568-C. The formula is based on assumed minimum
values at 0.772 MHz of 43 and 64 dB for Categories 3 and 5, respectively. The NEXT loss of the worst pair combi-
nation, for a length greater than or equal to 100 m (328 ft), is used. Acceptable values of NEXT loss are a greater
(or equal) dB value than shown in the table, or calculated from the formula, at a given frequency. The power-sum
method of measurement is used for backbone cables.
When the SRL value is higher than the limit, it indicates that the impedance varia-
tion is better than required for the cable pair. The limit applies to the worst pair of
the cable, so all pairs must be tested.
Because the twist pitch (lay length) of different pairs is varied to decrease
NEXT coupling, each pair of a cable will show a variation in values of most of the
measurement parameters. Some of the standard's limits are based on the worst pair's
value, while others, such as attenuation, require all of the pairs to be at least as good
as the limit value. This intentional difference in cable geometry also contributes to
some of the variations we see in the SRL.
Patch cords and cross-connect jumper wires must meet the requirements of
horizontal cable, with some exceptions. It is assumed that the patch cords will use
