Keysight U3401A, User And Service Manual

Page: 47 / 99

Operations and Features 2
Keysight U3401A User’s and Service Guide 47
dBm
The logarithmic dBm (decibels relative to one milliwatt) scale is often used in RF
signal measurements. The multimeter’s dBm operation takes a measurement and
calculates the power delivered to a reference impedance (typically 50, 75 or 600
Ω
)
.
The formula used for conversion from the voltage reading is:
dBm = 10 x Log
10
[1000 x (Reading
2
/ reference impedance)]
Figure 2-1 Typical dBm operation display
The default reference impedance value is 600
Ω
.. You can select the following
21 reference impedance values:
2
Ω , 4 Ω , 8 Ω, 16 Ω , 50 Ω , 75 Ω , 93 Ω , 110 Ω , 124 Ω, 125 Ω , 135 Ω , 150 Ω , 250 Ω,
300 Ω, 500 Ω, 600 Ω , 800 Ω , 900 Ω , 1000 Ω , 1200 Ω , 8000 Ω .
The dBm operation can be applied to DCV, ACV and DCV + ACV measurement
functions only. The multimeter displays the dBm modifier on the primary display
and displays the reference impedance selection on the secondary display.
Procedure 1
1 Press to enable the dBm modifier mode and dBm operation.
2 Use and to select the desired reference impedance.