Measurement Resolution And Measurement Speed; Resolution Bandwidth - Agilent Technologies 89410A Operator's Manual

Fundamental Measurement Interactions

Measurement Resolution and Measurement Speed

You should understand the interactions and limits related to measurement
fundamentals in order to optimize your measurements . These fundamentals affect
measurement speed, measurement resolution, and display resolution. If you are
familiar with either swept-tuned or FFT spectrum analyzers, you will find both
similarities and differences in the 89400 series analyzers. In any case, you should
become acquainted with the material in this section in order to be comfortable with
measurements in the 89400 series analyzers.
Resolution bandwidth, frequency span, main length, and window selection are
closely related in determining measurement resolution and measurement speed.
The flexible display resolution also affects your perception of measurement results.

Resolution bandwidth

Resolution bandwidth—often called RBW—determines the analyzer's frequency
resolution. It may also affect how fast the analyzer makes a measurement.
Normally, resolution bandwidth is adjusted automatically as you select different
frequency spans. Resolution bandwidth is one of the most important parameter
settings in a spectrum analyzer.
Because resolution bandwidth may also affect measurement time, manually
selecting a narrower resolution bandwidth can slow down a measurement more
than necessary. Selecting a resolution bandwidth that is too wide, on the other
hand, may not provide adequate frequency resolution and can obscure spectral
components that are close together.
Narrowing the resolution bandwidth lowers the noise floor because there is less
noise power within the bandwidth of a narrower filter. This occurs because noise
is equally distributed across the frequency spectrum, so the noise floor is lowered
as you progressively restrict the range of frequencies fed to the detector algorithm.
In most analyzers, the final IF filters determine the resolution bandwidth, but in the
89400 series analyzers the time record length and window shape determine the
resolution bandwidth—resolution bandwidth is largely independent of the span.
Resolution bandwidth is related to the number of frequency points and span only
when it approaches minimum and maximum limits. You will learn more about this
later in this chapter.
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