Null; Dbm - Agilent Technologies 34405A User's And Service Manual

Null

When making null measurements, also called relative, each reading is the
Null
Null
difference between a stored null value and the input signal. For example,
this feature can be used to make more accurate resistance measurements
by nulling the test lead resistance.
After you enable the Null operation, the multimeter stores the next
reading into the Offset register and immediately displays on the primary
display:
Primary Display = Reading - Offset
You can view and edit the Offset value in the secondary display as
described in
The multimeter allows Null settings for the following measurement
functions: DC Volts, AC Volts, DC Current, AC Current, Resistance,
Frequency, Capacitance and Temperature.

dBm

dBm The logarithmic dBm (decibels relative to one milliwatt) scale is often
Shift
used in RF signal measurements. The multimeter's dBm operation takes a
MnMx
measurement and calculates the power delivered to a reference resistance
(typically 50, 75 or 600W). The formula used for conversion from the
voltage reading is:
You can choose from several reference resistance values:
R
250Ω, 300Ω, 500Ω, 600Ω, 800Ω, 900Ω, 1000Ω, 1200Ω, or 8000Ω.
Numeric results are in the range of ± 120.000 dBm with 0.01 dBm
resolution shown, independent of the number of digits setting.
You can view and select the R
described in
34405A User's and Service Guide
"Editing Values in the Secondary Display"
= 10 x Log
dBm
10
= 2Ω, 4Ω, 8Ω, 16Ω, 50Ω, 75Ω, 93Ω, 110Ω, 124Ω, 125Ω, 135Ω, 150Ω,
REF
"Editing Values in the Secondary Display"
2
[ (Reading / R
REF
value in the secondary display as
REF
Features and Functions
on page 40.
/ 0.001W ]
)
on page 40.
2
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