Attenuation; Crosstalk; Dc Cable Tests; Ac Or Dc Voltage On Signal Wires - IBM 5500 Operational, Installation, And Maintenance Manual

Attenuation

Crosstalk

DC Cable Tests

AC or DC Voltage on Signal Wires

Minimum Cable Distances from Induced Noise Sources

Erratic performance
In extreme cases, an inoperative network or attached device
Excessive attenuation (signal loss) can be caused by:
• The attenuation characteristics of the cable
• Wire that is too small
• Impedance discontinuities
Excessive attenuation will limit the drive capability below the specified
allowable distances.
Excessive near-end crosstalk is a function of the design and manufacture of
the cable. Excessive crosstalk can cause:
• High error rates
• An inoperative network or attached device
• In extreme cases, false readings from the diagnostic procedures
To check the DC continuity of a cable run, power the devices off. Unplug the
power cords of all devices on that cable run and remove the twinax cable from
the 5500 Control Unit twinax connector. As most meters use a voltage to
measure resistance, you will get incorrect results if there is any voltage
present on the cable that you are testing.
The following voltages (depending on the magnitude) can be a safety hazard,
introduce errors into the network, or cause the network to be inoperative:
• AC voltage induced into the signal wires from nearby power or signal
cables
• AC or DC voltage caused by shorts or unintentional connection to other
circuits.
With the5500 Control Unit, any induced voltages in the twinax cable shields
are collected at the twinax connector box, and passed up the cable to the card
connector. From the card connector, these voltages dissipate through the card
bracket to the unit's chassis ground. If these voltages exceed certain levels,
problems can occur for other cards in the 5500 Control Unit. In these
conditions, the reason for the induced voltages must be located and resolved.
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