Filter
Top Products
1278
Sweep/Control
More Information
An FFT measurement can only be performed over a limited span known as the “FFT segment”. Several
segments may need to be combined to measure the entire span. For advanced FFT control in the
X-Series, you have direct control over the segment width using the
FFT Width control. Generally, in
automatic operation, the X-Series sets the segment width to be as wide as possible, as this results in the
fastest measurements.
However, in order to increase dynamic range, most X-series models provide a set of analog prefilters that
precede the ADC. Unlike swept measurements, which pass the signal through a bandpass before the
ADC, FFT measurements present the full signal bandwidth to the ADC, making them more susceptible
to overload, and requiring a lower signal level. The prefilters act to alleviate this phenomenon - they
allow the signal level at the ADC to be higher while still avoiding an ADC overload, by eliminating
signal power outside the bandwidth of interest, which in turn improves dynamic range.
Although narrowing the segment width can allow higher dynamic ranges some cases, this comes at the
Max: The maximum available FFT width is dependent on the IF Bandwidth option.
The maxim mum available width is:
Option B10, 10 MHz;
Option B25, 25 MHz,
Option B40, 40 MHz.
Backwards Compatibility SCPI: [:SENSe]:SWEep:FFT:SPAN:RATio <integer>
[:SENSe]:SWEep:FFT:SPAN:RATio?
This is the legacy “FFTs per Span” command, because in the PSA, this is what
you set rather than the FFT Width. The behavior of the analyzer when it
receives this command is to compute the “intended segment width” by
dividing the Span by the FFTs/Span parameter, then converting this intended
width to an actual width by using the largest available FFT Width that is still
less than the intended segment width. The “Span” used in this computation is
whatever the Span is currently set to, whether a sweep has been taken at that
Span or not.
Initial S/W Revision: Prior to A.02.00
Modified at S/W Revision: A.04.00
Key Path:
Sweep/Control, Sweep Setup
Remote Command: [:SENSe]:SWEep:FFT:WIDTh:AUTO OFF|ON|0|1
[:SENSe]:SWEep:FFT:WIDTh:AUTO?
Example: :SWE:FFT:WIDT:AUTO ON
Couplings: Pressing Auto Couple always sets FFT Width to Auto.
Preset: ON
State Saved: Saved in instrument state
Initial S/W Revision: Prior to A.02.00