Fluke 990DSL, Руководство пользователя, Страница: 169 / 242

XDSL Testing and Loop Qualification
The XDSL Toolbox
5
5-31
To view a continuous noise measurement at a selected frequency , move the
cursor to the desired frequency, and press
C
(
Contin. WB Noise
). The signal
level at the selected frequency is continuously displayed in large numerals,
along with a peak-detecting bar graph.
To save the displayed waveform in the Frequency Graph memory, press
L
.
WB Noise/Level Test Results for a Working ADSL Pair
Figure 5-16 shows results from a WB Noise / Level test on an active ADSL
line, in the
Bridged
termination mode, with ADSL/2 Target Service Type.
Results obtained from running a bridged WB Noise / Level test on a working
ADSL circuit can help you determine why the circuit is not performing “up to
speed”, when other line characteristics indicate that it should be. This non-
intrusive test can often be used to diagnose excessive bridged tap, interference
from other data circuits or AM radio signals, or defective modems as the cause
of a performance problem.
The
A
(
Zoom
) and
B
(
Disturber Mask
) keys operate as described earlier.
To continuously monitor any one of the DMT bin signals, move the cursor to
the desired frequency, then press
C
(
Contin. WB Level
). Instantaneous
variations in frequency bins can be caused by impulse noise. If such variations
are observed, you can measure them by running an Impulse Noise test (see
“Impulse Noise Test” for details).
To run a WB Noise / Level Test on an ADSLx line having a connected ADSLx
modem, select
ADSLx Modem Filter = Y
in the
Setups
menu, disconnect the
DSLAM, and then run the test. The measurement will then automatically avoid
the time intervals during the modem’s training tones, resulting in a clean
measurement of only the quiescent background noise.