DLS DLS 400A, Руководство по эксплуатации

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Appendix E
Page 205
Q) Does the loop selected affect the noise level output by the Impairments module?
A) Yes. Since impairments are injected from a 4.05 k
Ω
impedance, the power injected on
to the loop depends heavily on that impedance. Different loops have different imped-
ances.
Q) Why is the noise not at the calibrated level when injected on to a simulated line?
A) No real loop provides the same load as the one used for calibrating the module, with
the possible exception of the ANSI special load, and one of the ANSI loops.
Q) Why do I have to use a balanced meter to measure noise levels from the DLS 400?
What happens if I just use the meter that I already have?
A) The Transmitters/Receivers under test provide a balanced load, so we should measure
them the same way. Most meters ground one connection. This upsets the simulation at
higher frequencies. Even if the meter is floating, it may be that capacitance to ground
from one lead is more than the other, and this can lead to incorrect results.