Keysight V3500A, Руководство пользователя

Страница: 107 / 122

RF Measurement Basics 4
V3500A User’s Guide 87
Power of various types of signals
Continuous-wave signals
Continuous- wave (CW) signals are the simplest form of RF
signal. CW signals consist of a constant sine wave. Power
measurements on this type of wave result in a single
numerical value.
Modulated signals
Modulated signals are sinusoids whose amplitude, phase, or
frequency change with respect to time. Changes in either the
phase or frequency do not change the power of the signal,
but changes in amplitude causes change in the power level.
Two approaches can be taken to characterizing the power of
modulated signals:
• Peak power meter
A peak power meter measures the power of the signal
very rapidly (faster than the rate at which the modulation
changes). The results can then be displayed in a graph of
power versus time similar to an oscilloscope display. This
approach has the advantage of displaying a great deal of
information. One disadvantage is that the results can be
difficult to interpret — especially for the complex
modulation schemes in use today.
•
Average power meter (the V3500A takes this approach)
An averaging power meter measures the power versus
time of the signal, but then averages the result —
condensing the measurement to a single number. The
V3500A is an averaging power meter. In effect, the power
meter performs the following calculation:
where
P(t) is the power of the modulated signal as a function
of time.
P
avg
1
T
---
P t
( )
t d
0
T
∫
=