Agilent Technologies Signal Analyzer N9030a - Manual (Page 1178)

6 RLC Swept SA Measurement Front-Panel & SCPI Reference
Sweep/Control
drive level. If you reduce the width of an FFT, an analog filter is placed before the ADC that is
about 1.3 times as wide as the FFT segment width. This spreads out the pulsed RF in time and
reduces the maximum signal level seen by the ADC. Therefore, the input attenuation can be
reduced and the dynamic range increased without overloading the ADC.
Further improvement in dynamic range is possible by changing the FFT IF Gain (in the Meas Setup
menu of many measurements). If the segments are reduced in width, FFT IF Gain can be set to High,
improving dynamic range.
Depending on what IF Bandwidth option you have ordered, there can be up to three different IF
paths available in FFT sweeps, as seen in the diagram below:
The 10 MHz path is always used for Swept sweeps. It is always used for FFT sweeps as well,
unless the user specifies ~25 MHz in which case the 25 MHz path will be used for FFT sweeps, or
~40 MHz, in which case the 40 MHz path will be used for FFT sweeps. Note that, although each of
these keys picks the specified path, the analyzer may choose an FFT width less than the full IF
width, in order to optimize speed, trading off acquisition time versus processing time.
FFT Width
This menudisplays and controls the width of the FFT’s performed while in FFT mode. The “FFT
width” is the range of frequencies being looked at by the FFT, sometimes referred to as the “chunk
width” -- it is not the resolution bandwidth used when performing the FFT.
It is important to understand that this function does not directly set the FFT width, it sets the
limit on the FFT Width. The actual FFT width used is determined by several other factors
including the Span you have set. Usually the instrument picks the optimal FFT Width based on
1178 Remote Language Compatibility Measurement Application Reference