Keysight U3402A - Dbm; Figure 2-1 Typical Dbm Operation Display

Operations and Features 2
Keysight U3402A User’s and Service Guide 53
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, or 8000 Ω.
If reference impedance 2 Ω, 4 Ω, 8 Ω, or 16 Ω is selected, the dBm operation is
displayed in watt (power).
Numeric results are in the range of ±120.000 dBm with 0.01 dBm resolution
shown, independent of the number of digits setting.
The dBm operation can be applied to DCV and ACV measurement functions only.
The multimeter displays the dBm operation on the primary display and displays
the reference impedance selection on the secondary display.
Procedure 1
1 Press to enter dBm operation.
2 Use and
to select the desired reference impedance.
3 Press to store the selected value and read the display.