DLS DLS 400A, Operating Manual

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ADSL NOISE GENERATOR DESCRIPTION
Page 55
WARNING
Inserting the longitudinal mode transformer in the loop provides additional loop attenua-
tion which is not present when the transformer is switched out of the loop. The effective
attenuation depends on the bandwidth of the signal passing through the loop, but is in the
region of 1 to 4 dB. This alone accounts for some reduction in margin. When using longi-
tudinal mode you can determine how much reduction in margin is due to the transformer
by switching it in circuit, impressing 0 Volts of longitudinal mode voltage on the line, and
running a test like this. Then you can run with longitudinal voltage as well, to determine
additional degradation due to the longitudinal voltage.
6.12.3 DLS 200 Mode Crosstalk and White Noise
All 3 crosstalk generators and the white noise generator are based on noise produced by
Pseudo Random Binary Sequences. This base noise is then used to create the appropriate
crosstalk and white noises. Some customers expressed a desire for the noises generated by
the DLS 400 to produce exactly the same effects as noises that come from a DLS 200H.
To do this we introduced a DLS 200 compatible noise, in which the base noise is modified
from the original DLS 400 base noise.