Triple-Play Service Deployment

Chapter 4: Troubleshooting the Copper Plant for IP Services
To get accurate readings, these measurements must be made with
the line dialed into a quiet termination state reached by dialing a
quiet termination number. No termination or the wrong
termination may result in a higher than actual reading of noise on
the circuit. And there are limitations to the conventional balance
test as well. The most significant is that this technique requires a
certain amount of power influence to obtain a good balance
reading. Too little power influence results in balance results that
are lower than the actual values. For example, if the power
influence is only 50dBrnc, the best possible balance reading
would be 50dB even if the noise is 0.
Longitudinal balance
Longitudinal balance is similar to circuit balance, except the
power influence limitation mentioned above is overcome
because the test set applies a signal to the pair that takes the
place of power influence in measuring the pair’s ability to reject
noise. During the longitudinal balance test, a 1,000 Hz (1 KHz) tone
is applied by the test set to the pair under test from tip to
ground and ring to ground, then the set measures the level of
induced noise on the pair. A calculation of the balance is
performed and displayed. This method also enables accurate
measurements on unterminated lines. The measurement is given
in decibels, with 60 dB or greater generally considered acceptable,
50 to 60 dB marginal, and less than 50 dB unacceptable.
Resistive balance
Balance can also be measured using a resistive measurement by
grounding both conductors at the far end and comparing tip-toground
and ring-to-ground measurements. These measurements
should be within 5 Ω or 1% of each other, whichever is less. This
measurement requires intervention at the far end of line, so it is
often replaced by a longitudinal balance measurement.
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