Fluke 990DSL, Руководство пользователя

Страница: 147 / 242

XDSL Testing and Loop Qualification
DSL Auto-Test
5
5-9
The
HDSL2
Loss test (using
Predefined
thresholds) runs a comprehensive
multi-frequency Loop Attenuation test on the pair. It does this, rather than
making the traditional single-frequency Nyquist Loss measurement, in order to
more effectively qualify the pair
specifically for HDSL2 service. The same
approach is used for
HDSL4
service qualification.
The Loop Attenuation values displayed in the upper right corner represent an
average value of the pair’s loss across the Upstream and Downstream
frequency bands. In this example, both the Upstream and Downstream Loop
Attenuation values are greater than the Pass thresholds, and are displayed in
flashing reverse-video format.
5. To superimpose a transmitted Power Spectral Density (PSD) mask on the
Loop Attenuation graph, press
B
(
PSD Atten Mask
) and then press
G
or
I
to overlay either the Upstream or Downstream mask on the graph.
Figure 5-4 shows the Loop Attenuation graph with the superimposed
Downstream PSD mask.
•
The graph itself shows the pair’s attenuation across the frequency
bands utilized by the HTU-C (Downstream) and HTU-R (Upstream)
equipment.
•
The PSD masks show the relative signal power transmitted across the
bands by the HTU-C (Downstream) and HTU-R (Upstream)
equipment.
•
From visually observing the graph and superimposed mask, it can be
seen that the more
dark area under the mask curve, the more likely
the pair will be able to carry HDSL2 service due to the lower loss
across the band of interest. Conversely, the more
light area under the
mask curve (as in the above example, from 270 to 420 kHz), the less
likely the pair will be able to reliably carry HDSL2 traffic. This is
confirmed by the failure of this test.
6. Press
L
to save the waveform in the
Frequency Graph
storage memory.