Keysight V3500A, Руководство пользователя

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84 V3500A User’s Guide
4 RF Measurement Basics
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
P
1
and P
0
are the two power levels to be compared.
Absolute measurement can be made on the decibel scale by
using a standard power level in place of
P
0
. If P
0
is defined
to be 1 milliwatt, the resulting units are called “dBm.” Power
expressed in dBm is calculated with the formula:
10
10
P
1
P
0
------
⎝ ⎠
⎛ ⎞
log ×
P
dBm
10
10
P
1
1 mW
-------------
⎝ ⎠
⎛ ⎞
log × =