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8163A/B, 8164A/B, 8166A/B User’s Guide
7
Return Loss Measurement
Figure 104
Keysight 8161x Details Screen
Set Wavelength
1 Move to [
λ
] and either:
•
set this parameter to
Extern
.
•
choose an internal source by selecting its wavelength.
2 Enable the source.
T-Value
The T-value can be described as the effective return loss of a system, with
all internal parasitic reflections taken into account, in one parameter. The
system's internal parasitic reflections include backscattering in the
measurement patchcord, reflections due to imperfect directivity of the
internal couplers, reflections at internal terminations, reflections at
connector ends and diodes. Intuitively, one could call the T-value the
"noise" of the system (set up). The T-value is used to evaluate how well the
calibration was done, and thereby provide information on how high return
losses (low reflectances) can be measured. The correlation between the
T-value and the displayed return loss is that the power that corresponds to
the T-value (system "noise") is subtracted from the power that
corresponds to the measured return loss at the return loss diode, yielding
the actual return loss. When the actual return loss is high, then this
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