8163A/B, 8164A/B, 8166A/B User’s Guide 101
Power Measurement 3
4 Press the [Close] softkey to exit the menu.
How to Set the Power Unit
Pressing the Power Unit softkey allows you to select either W, dB, or dBm
as the units in which power is displayed. The Power Unit softkey is visible
when you 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 How to Input a
Reference Level on page 103.
P
dB
10
P
input
W()
P
ref
W()
-------------------------log=
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