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FFT
R&S
®
RTM20xx
117
User Manual 1317.4726.02 ─ 01
"Envelope"
In addition to the normal spectrum, the maximal oscillations are saved
separately and updated for each new spectrum. The maximum values
are displayed together with the newly acquired values and form an
envelope. This envelope indicates the range of all FFT trace values that
occurred.
If any signal parameters are changed, the envelope is reset.
"Average"
The average of several spectrums is calculated. The number of spec-
trums used for the averaging is defined using the knob or the "No. of
Averages" softkey. This mode is useful for noise rejection.
Remote command:
No. of Averages
Defines the number of spectrums used for averaging.
This function is only available if "Average" mode is selected.
Remote command:
Window
Window functions are multiplied with the input values and thus can improve the FFT
display.
If discontinuities occur at the borders of the measurement interval, the algorithm interprets
such discontinuities as a sudden edge, which can distort the result. For bell-shaped func-
tions, the border values are multiplied with smaller values and thus have less influence
on the result.
"Hanning"
The Hanning window is bell shaped. Unlike the Hamming window, its
value is zero at the borders of the measuring interval. Thus, the noise
level within the spectrum is reduced and the width of the spectral lines
enlarges. Use this window to measure amplitudes of a periodical signal
precisely.
Reference for FFT key