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.
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