Fluke 990DSL, User Manual

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990DSL
Users Guide
5-10
DSL Auto-Test Results: ADSL Service Type
The ADSL Loss test (using
Predefined
thresholds) also runs a comprehensive
multi-frequency sweep on the pair. It does this rather than making traditional
single-frequency Nyquist Loss measurements at the Upstream (138 kHz) and
Downstream (1100 kHz) frequencies, in order to more accurately estimate the
achievable Upstream and Downstream data rates on the pair.
The process is as follows:
First, loss values at each DMT frequency (tone) bin, along with Wideband
Noise measurement data for each bin, enable the tester to generate a Signal-to-
Noise Ratio (SNR) graph as shown in Figure 5-5.
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Figure 5-5. DSL Auto-Test Loss Results: ADSL SNR Graph
From the SNR values, the tester generates a
Bits / Tone
graph (see Figure
5-6), showing the number of data bits able to be encoded at each bin.
Estimated Upstream and Downstream data rates (shown in the upper right
corner of Figures 5-5 and 5-6) are generated from the aggregate of
encoded data bits across both of the bands.