Operations and Features 2
U3402A User’s and Service Guide 21
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 W). 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 W. You can select the following 21
reference impedance values:
2 W, 4 W, 8 W, 16 W, 50 W, 75 W, 93 W, 110 W, 124 W, 125 W, 135 W, 150 W, 250 W,
300 W, 500 W, 600 W, 800 W, 900 W, 1000 W, 1200 W, or 8000 W..
If reference impedance 2 W, 4 W, 8 W, or 16 W 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.
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