Chapter 18 Maintenance and Troubleshooting
Resolving problems
SmartClass TPS User’s Guide
June 2014 22035456, Rev 001 157
This would indicate some imbalance in the quality of each lead and reduced noise immunity.The
more each lead is electrically identical (capacitance, inductance, impedance), the better the pair will
resist induced noise. If they do not cancel induced noise equally, the difference is realized as
unwanted current, or metallic or mutual noise. If the imbalance of the leads is too great, the
customer would hear noise.
Issue
The POTS service test is fine but the DSL signal cannot be detected at the NID. The test set indi-
cates 2 load coils on a 15 kft loop.
Resolution
Load coils block high frequency signals such as DSL and they must be removed for digital circuits.
In a normal loading scheme, the first one will be 3 kft from the CO and the second will be 9 kft from
the CO. Use a tester that has TDR capability to verify the location of the loads. Loads are used to
improve POTS over long loops. On most loops 18 kft or longer, load coils are required to ensure
voice quality. Load coils must be evenly spaced starting at 3 kft from the CO and placed at 6 kft
intervals thereafter, with at least 2,000 feet between the last load coil and the customer premises.
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