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impedance is applied. The relationship between dBm, reference impedance, and the voltage is defined by
the following equation:
Where:
V
is the DC or AC input signal voltage value. Z
IN
If a relative value is in effect when dBm is selected, the relative value will be converted to dBm value before
REL is applied. If REL is applied after dBm has been selected, dBm has REL applied to it directly.
To set the reference impedance, perform the following steps:
1. Press Shift → mX+b, the voltage reference value for dB math function will be displayed.
2. Press Auto (ENTER) to confirm the voltage reference value, now you have selected the dB math
function.
3. Press Shift → mX+b again, the present impedance reference value for dBm math function will be
displayed: REF：0000
4. Use
and
decrement the digits. Enter a value from 1Ω to 9999Ω.
5. Press Auto (ENTER) to confirm the reference impedance, the message "CHANGE SAVED" will be
displayed for a moment. DMM returns back to the measurement status.
6. DMM will display the result of the dBm calculation.
If you want to change the impedance reference value after the dBm function is enabled, you can take
actions as below:
1. Press Shift →
2. Press
to enter the parameter level, and the present impedance reference value will be displayed:
REF: 0000.
3. Use
and
or decrement the digits. Enter a value from 1Ω to 9999Ω.
4. Press Auto (ENTER) to confirm the reference value, the message "CHANGE SAVED" will be displayed
for a moment, and DMM will return to the command level. Press Trig (ESC) to cancel the reference
value input, DMM returns back to the command level without changing the reference value.
5. Press Shift →
NOTES: The reference impedance and input impedance mentioned in this chapter are totally
different. Input impedance is inherent in the instrument and could not be changed via
foregoing methods.
dBm is valid for both positive and negative DC voltage.
The mX+b and percent math operations are applied after the dBm or dB math. For example,
if mX+b is selected with m=10 and b=0, the display will read 10.000MXB for a 1VDC signal.
If dBm is selected with
keys to choose a numerical place and use
to enter the command level, "5: dBm REF " will be displayed.
keys to choose a numerical place and use
key to exit the menu and return to the dB math operation status.
（
= 50Ω
Z
REF
is the specified reference impedance.
REF
）
, the display will read 130MXB.
ABM-4082
and
keys to increment or
and
keys to increment
31
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