Rohde & Schwarz R&S UPP, Руководство пользователя

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Instrument Functions
R&S
®
UPP
409 User Manual 1411.1055.32 ─ 10
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The "FFT as measurement function" (Function FFT) is, like the Post FFT, also cal-
culated with double precision but additionally allows a number of other functions
such as averaging and undersampling (limiting the frequency range to increase the
frequency resolution) as well as free selection of the FFT size and window. The
Function FFT is displayed in the "FFT Function" graphical window.
5.26.1 Size of the FFT
The size of the FFT together with the sampling rate and bandwidth determines the
length of the measurement interval (integration time) and thus the frequency resolution
of the calculated spectrum. The following correlations apply:
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Integration time = FFT size / Sampling rate
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Number of lines = FFT size / 2
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Frequency resolution = Sampling rate / FFT size = 1 / Integration time
Therefore, if a higher sampling rate and bandwidth are used, a higher FFT size will be
required to produce the same frequency resolution.
Other variables which appear as display fields in the group of FFT parameter fields are
derived from the FFT size, see "Resolution" and "Meas Time".
In the analog analyzer, the internal sampling rate is determined by the selected band-
width.
FFT Size
Size of the "Function FFT", can be set in powers of 2 from 512 (0.5 k) to 256 k.
Not only the integration time but also the time required to calculate the transformation
and graphical display increase with increasing FFT size. This results in a disproportion-
ate increase in the total measurement time. Unnecessarily high FFT sizes should
therefore be avoided in order to reduce the measurement time.
Note: For the Post FFT, no fixed "FFT size" but only a (variable) lower limit ("Min FFT
Size") can be entered. The measurement function carried out in each case can dynam-
ically increase the FFT size as a function of the sample signal frequency.
Other variables which appear as display fields in the group of FFT parameter fields are
derived from the "FFT size":
Remote command:
SENSe[1]:FUNCtion:FFT:SIZE
on page 763
FFT Analysis