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Shielded Twisted Pair Cable Specifications
STP Cable Characteristics
42
IBM 8265: Planning and Site Preparation Guide
With the introduction of 100Mbps FDDI and ATM Networks using STP cable between
hubs and workstations, the following specifications must be met.
At IBM's request, Engineering Testing Laboratories (ETL) and Underwriters
Laboratories (UL) have begun certifying cable according to the electrical
specifications in the following sections. Contact your IBM representative or nearest
branch office for a list of cable manufacturers whose STP cables have been certified
using the new specifications.
Capacitance Unbalance
The capacitance unbalance of any pair, at 1 kHz and measured at a temperature of
25° ± 3°C, may not exceed 1000 pf/km. The measurements are to be performed on
both 305 m (or greater) reels and 100 m reels.
Resistance
The dc resistance of a conductor measured at a temperature of 25° ± 3°C has a
maximum value of 57.1 ohms/km for Type 1A, and 151 ohms/km for Type 6A and
Type 9A.
Resistance Unbalance
The maximum % dc resistance unbalance between the two conductors of a pair as
measured on 305 m (or greater) reels and 100 m reels is 4%. The % resistance
unbalance is defined to be:
(
Maximum Resistance Minimum Resistance
------------------------------------------------------------------------------------------------------------------------------------------- -
Minimum Resistance
Balanced Mode Attenuation
Balanced mode attenuation must be made with the cable-driven (source) and
monitored (output) in a balanced mode and with the cable shield earthed (grounded)
to the source and measuring instrument earth. Impedance matching baluns must be
used for balanced mode. Baluns must be selected to match the nominal cable
impedance at the frequency of interest to the impedance of the source and/or
measuring equipment. Balun losses and differences in signal levels due to the
impedance transforming characteristics of the baluns must be taken into account.
A standard S-parameter network analyzer may be used to perform these tests.
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