Power Measurement
How to Measure Power
72
Agilent 8163A Lightwave Multimeter, Agilent 8164A Lightwave Measurement
System, & Agilent 8166A Lightwave Multichannel System, Fourth Edition
move to the [
P
] or [
Ref
] parameters. alternatively the Power Unit can be changed
by using the Power Meter menu.
What are the Power Units ?
Watts (W) are the SI unit for power measurement.
You can also measure power in dB or dBm. Values displayed in these units are
derived from measurement in Watts.
By selecting dBm, the following calculation is made:
Where,
P
dBm
is the power value displayed in dBm, and
P
input
is the input signal level in Watts.
Power, in units of dBm, is measured relative to 1 mW, it is an absolute power
measurement.
By selecting dB, the following calculation is made:
Where,
P
dB
is the power value displayed in dB,
P
input
is the input signal level in Watts, and
P
ref
is the chosen reference power value in Watts.
Power, in units of dB, is measured relative to a particular reference power value.
For information on selecting this reference value, see
To set the power unit to dBm:
1
Move to the [
P
] parameter and press the [Power Unit] softkey. You will see the
menu in Figure 43.
P
d Bm
10
P
i np ut
W
( )
1
10
3
–
W
( )
×
------------------------------
log
=
P
d B
10
P
in pu t
W
( )
P
ref
W
( )
-------------------------
log
=
