Rohde & Schwarz R&S FSP Series, Operating Manual

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R&S FSP Getting Started
Measurements on Modulated Signals
2.36 Operating Manual 1164.4556.12 - 06
Fig. 2-2 Measuring adjacent channel power in time domain (Fast ACP)
As the resolution bandwidth is much wider than the one used for the integration
method, the results are much more stable when compared at the same sweep
time.
Repeatability can be influenced by the selected sweep time. The results
become much more stable if long sweep times are selected. Since the
amplitude distribution is different in different channels (part of the modulation
spectrum falls within the first adjacent channel), the repeatability depends on
the spacing of the measured channel from the transmit channel.
Fig. 2-3 below shows the standard deviation of results in the different channels
as a function of the selected sweep time. The standard deviation for the
various sweep times was recorded using a signal generator as a source. With
real DUTs the amplitude distributions in adjacent channels may be different so
that the standard deviation could differ from that shown in
Fig. 2-3 . To evaluate
the correct measuring time for time-critical measurements at a given standard
deviation, the standard deviation of the ACP values at the output of the real
DUT must be determined.
Fig. 2-3 Standard deviation of the results of Fast ACP measurement as a function of
selected sweep time evaluated from 100 measurements per sweep time
NADC Repeatability
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0.6
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1
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1.4
10 100 1000
Sweep Time / ms
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ta
nda
rd
D
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Alt1 Channels
Adj Channels
Tx Channel