Keysight U1281A Guide De L'utilisateur page 62

2 Making Measurements
Making dB Measurements
Your multimeter is capable of displaying voltage as a dB value, either relative to 1 milliwatt
(dBm) or a reference voltage of 1 volt (dBV).
To set the multimeter to display values in either dBm or dBV, first set up your multimeter to
measure voltage as shown in Figure 2-2 or Figure 2-7. Probe the test points, and read the
display. Then, press and hold
until the voltage measurements are displayed either as a dBm value (see Figure 2-11) or a
dBV value (see Figure 2-12)
Table 2-5
Legend
mV
– A dBm measurement must use a reference impedance (resistance) to calculate a dB
NOTE
value based on 1 milliwatt. The reference impedance is set to 50 Ω by default. To select
another reference value, see the "Setting a custom dBm reference impedance" on
page 126.
– A dBV measurement uses a 1 volt reference voltage to compare the present
measurement against a stored relative value. The difference between the two AC
signals is displayed as a dBV value. The reference impedance setting is not part of a
dBV measurement.
62
Rotary switch positions allowing dBm or dBV measurements
Default function
AC V
V
AC mV
DC V
V
DC mV
mV
for more than 1 second to scroll through the options
Function when
AC V with LPF
AC mV with LPF
Scrolls between
– AC V
– AC+DC V, or
– DC V
Scrolls between
– AC mV
– AC+DC mV, or
– DC mV
Keysight U1281A/U1282A User's Guide
is pressed
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