Power Measurement How to Measure Power
74 Agilent 8163A Lightwave Multimeter, Agilent 8164A Lightwave Measurement
System, & Agilent 8166A Lightwave Multichannel System, Fourth Edition
How to Set the Reference Level
How to Input a Reference Level
dB results are shown relative to a reference level. The [Ref] parameter sets the
reference level. Setting, or changing, the reference only affects results that are
displayed in dB.
The reference level is displayed in units of dBm or Watts. Depending on which is
selected the following equations are used to calculate the power level in dB:
P
display
(dB) = P
measured
(dBm) − REF(dBm)
or
Where,
P
display
is the displayed relative power,
P
measured
is the absolute power level (see “How to Set the Calibration
Offset” on page 73), and
REF is the reference level.
You can choose the units for the reference using the Power Unit softkey. If you
choose dB, the power value changes to dB and the displayed reference level
changes to dBm.
To set the reference level to 10 mW:
1 Move to the Power Meter channel and press the [Details] softkey.
2 Move to the [Ref] parameter and press the [Power Unit] softkey.
3 Move to <W> and press Enter twice.
4 Change the units to mW using the [Unit+] and [Unit−] softkeys.
5 Enter 10.000 and press Enter.
How to Set the Reference Value to the Current Power
Value
In addition to entering a new reference value, you can change the reference value
to the currently displayed power value by pressing the [Dsp->Ref] softkey.
Pressing the [Dsp->Ref] softkey takes the input power level and stores it as the
reference. Setting the reference only affects results displayed in dB.
When you press the [Dsp->Ref] softkey, the absolute power level, the power
value in dBm or Watts, is stored as the reference, that is:
REF = P
measured
P
display
dB() 10
P
measured
W()
REF W()
----------------------------------log=
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