Meaning
Spectrum analyzer filter settings determine the width of the frequency band that is measured at any single instant during a sweep. When evaluating wireless devices for regulatory certification, the resolution bandwidth controls the ability of the test equipment to separate closely spaced frequency components. This parameter is specified by standards bodies such as the FCC to ensure consistent measurements of spurious emissions.
Sweep Time Impact
Narrower filter settings increase the frequency resolution of the display but require a slower sweep rate to allow the internal filters to settle. If the resolution bandwidth is set too low for a given span, the sweep time increases exponentially, which extends the duration of compliance testing. Test engineers must balance resolution with testing speed by using automated routines that adjust the sweep rate dynamically.
Noise Floor Modification
The displayed average noise floor of the test instrument drops by ten decibels for every tenfold reduction in the filter width. Adjusting the resolution bandwidth is a standard method to expose weak spurious signals that would otherwise be hidden below the thermal noise of the analyzer.
Compliance Measurement
Certification standards dictate the exact filter settings that must be used for different frequency ranges, such as one hundred kilohertz for emissions below one gigahertz. Adhering to these defined resolution bandwidth values ensures that the test results from different laboratories can be compared directly during the product approval process.
