About SEM Multiband Measurements

Spectral Emissions Mask (SEM) supports multiple spectrum bands as provided in the Power Spectrum Measurement. The typical customer use case is to measure SEM scenarios where a single carrier is less than the hardware's maximum IF bandwidth, but the total of all carriers and offsets extends beyond the hardware's maximum IF bandwidth. SEM multiband also supports scenarios where a mixture of high and low power signals are present and either significantly different ResBW/VBW or range settings are required for different spectrum regions.

See Making Power Spectrum Measurements for more information.

Selecting a Multiband Mode

Single Spectrum is the default, most intuitive behavior. A single acquisition is used to capture all data required by the measurement to cover the time and frequency region implied by aggregate carrier and offset configuration.

Spectrum Channel per Region allows SEM measurements where a single acquisition cannot make the measurement (a NO DATA indicator will be displayed with a reason indicating the problem). Choosing a distinct spectrum index per region allows the span constraint to be applied to the associated spectrum region rather than the aggregate requirements of all regions. Spectrum Channel per Region may be faster or provide better dynamic range if the offset and carrier regions include large gaps in frequency or have very different power levels.

SEM Multiband-Related Parameters

The following SEM parameters are used to configure the spectrum index per region for multiband (Spectrum Channel per Region) measurements:

Spectrum Index

Lower Spectrum Index

Upper Spectrum Index

Parameters Affected by SEM Multiband

Res BW (Offsets Summary) - In single-spectrum mode when Detector for Offsets is set to Peak (MAX), Res BW is coerced to a single value for all offsets. With peak offsets, each offset needs to use a different spectrum channel in order to set Res BW independently for each offset. You can do this by setting the appropriate Acquisition Count and selecting Spectrum Channel per Region to configure a SEM multiband measurement.

Other Useful Parameters

Range - (Input > Analog > Range) Supports offsets and carriers that are widely spaced in frequency and power level.

Adjusting the Range setting implies attenuator changes during each measurement scan for some hardware, so care should be taken to minimize use of continuous measurement sweeps for this scenario to avoid undesired wear.

Extensions - (Input > Extensions) Instrument-specific Input Extension properties per spectrum region.

ResBW/Detectors - A subset of properties from the ResBW and Detectors panels (e.g., to enable different Points per spectrum region).

See Also

NO DATA Trace Indicator Messages and Measurement Warnings