Units Of Measurement; Watts; Decibels - Keysight V3500A User Manual

Units of Measurement

RF power measurements can be expressed in either Watts or dBm. The V3500A
can display results in either Watts
or dBm.

Watts

Watts are the standard SI unit for power measurements. In electrical terms, one
volt applied across a one-ohm resistor dissipates one watt of power.

Decibels

Decibels (abbreviated dB), are a logarithmic scale used to express power. Decibels
are inherently a ratio measurement providing the relative magnitude of two
different numbers.
For power measurements, the difference between two signals in decibels is:
where
Absolute measurement can be made on the decibel scale by using a standard
power level in place of P
called "dBm." Power expressed in dBm is calculated with the formula:
Keysight V3500A User's Guide
P 1
 
- - - -
×  
10 log
10 P 0
 
P and P are the two power levels to be compared.
1 0
×
P dBm = 10 log
10
. If P is defined to be 1 milliwatt, the resulting units are
0 0
P 1
 
- - - - - - - - - -
 
1mW
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