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dB Measurements
Each dB measurement is the difference between the input signal and a
stored relative value, with both values converted to dBm.
dB = reading in dBm – relative value in dBm
Applies to dc voltage and ac voltage measurements only.
• The relative value is adjustable and you can set it to any value
between 0 dBm and ±200.00 dBm.
• The relative value is stored in volatile memory; the value is cleared
when power has been off, after a remote interface reset, or after a
function change.
• The relative value is stored in the multimeter’s dB Relative Register.
There are two ways you can specify the relative value. First, you can
enter a specific number into the register from the front-panel menu or
from the remote interface. Any previously stored value is replaced
with the new value. If you are operating the multimeter from the front
panel, entering a relative value also turns on the dB function.
The second way to enter the relative value is to let the multimeter
take the first reading, convert it to dBm, and store that value in the
register. Changing the dBm reference resistance (see page 68) does
not change the stored relative value. After you enable dB, the first
reading taken will be 0 dB (if you have not changed the value stored in
the register). If you entered a number into the register, as described in the
paragraph above, the first reading does not overwrite the stored value.
• Front-Panel Operation: After enabling dB, you can edit the stored
relative value by pressing
Shift > (Menu Recall). Any previously
stored value is replaced with the new value. Turning on the menu
does not disable the dB operation; the multimeter will resume
taking measurements when you turn off the menu.
3: dB REL (MATH MENU)
See also “To Make dB Measurements,” on page 40.
3
Chapter 3 Features and Functions
Math Operations
67