getMeasurementsData

Get the current measurement data displayed on the spectrum analyzer

Syntax

data = getMeasurementsData(scope)

data = getMeasurementsData(scope,"all")

Description

data = getMeasurementsData(scope) returns a data table about the current spectrum analyzer measurements in use.

data = getMeasurementsData(scope,"all") returns a data table about all spectrum analyzer measurements for the current time step.

Examples

Obtain Measurements Data Programmatically for spectrumAnalyzer object

Compute and display the power spectrum of a noisy sinusoidal input signal using the spectrumAnalyzer MATLAB® object. Measure the peaks, cursor placements, adjacent channel power ratio, and distortion values in the spectrum by enabling these properties:

• PeakFinder

• CursorMeasurements

• ChannelMeasurements

• DistortionMeasurements

Initialization

The input sine wave has two frequencies: 1000 Hz and 5000 Hz. Create two dsp.SineWave System objects to generate these two frequencies. Create a spectrumAnalyzer object to compute and display the power spectrum.

Fs = 44100;
Sineobject1 = dsp.SineWave(SamplesPerFrame=1024,PhaseOffset=10,...
    SampleRate=Fs,Frequency=1000);
Sineobject2 = dsp.SineWave(SamplesPerFrame=1024,...
    SampleRate=Fs,Frequency=5000);
SA = spectrumAnalyzer(SampleRate=Fs,SpectrumType="power",...
    PlotAsTwoSidedSpectrum=false,ChannelNames={'Power spectrum of the input'},...
    YLimits=[-120 40],ShowLegend=true);

Enable Measurements Data

To obtain the measurements, set the Enabled property to true.

SA.CursorMeasurements.Enabled = true;
SA.ChannelMeasurements.Enabled = true;
SA.PeakFinder.Enabled = true;
SA.DistortionMeasurements.Enabled = true;

Use getMeasurementsData

Stream in the noisy sine wave input signal and estimate the power spectrum of the signal using the spectrumAnalyzer object. Measure the characteristics of the spectrum. Use the getMeasurementsData function to obtain these measurements programmatically. The isNewDataReady function returns true when there is new spectrum data. Store the measured data in the variable data.

data = [];
for Iter = 1:1000
    Sinewave1 = Sineobject1();
    Sinewave2 = Sineobject2();
    Input = Sinewave1 + Sinewave2;
    NoisyInput = Input + 0.001*randn(1024,1);
    SA(NoisyInput);
     if SA.isNewDataReady
        data = [data;getMeasurementsData(SA)];
     end
end

The panes at the bottom of the scope window display the measurements that you have enabled. The values in these panes match the values in the last time step of the data variable. You can access the individual fields of data to obtain the various measurements programmatically.

Compare Peak Values

Use the PeakFinder property to obtain peak values. Verify that the peak values in the last time step of data match the values in the spectrum analyzer plot.

peakvalues = data.PeakFinder(end).Value 

peakvalues = 3×1

   26.3957
   22.7830
  -57.9977

frequencieskHz = data.PeakFinder(end).Frequency/1000

frequencieskHz = 3×1

    4.9957
    0.9905
   20.6719

Obtain Measurements Data Programmatically for Spectrum Analyzer Block

Compute and display the power spectrum of a noisy sinusoidal input signal using the Spectrum Analyzer block. Measure the cursor placements, adjacent channel power ratio, distortion, and peak values in the spectrum by enabling these block configuration properties:

• CursorMeasurements

• ChannelMeasurements

• DistortionMeasurements

• PeakFinder

Open and Inspect the Model

Filter a streaming noisy sinusoidal input signal using a Lowpass Filter block. The input signal consists of two sinusoidal tones: 1 kHz and 15 kHz. The noise is white Gaussian noise with a mean of 0 and a variance of 0.05. The sampling frequency is 44.1 kHz. Open the model and inspect the parameter values in the blocks.

model = 'spectrumanalyzer_measurements.slx';
open_system(model)

Access the configuration properties of the Spectrum Analyzer block using the get_param function.

sablock = 'spectrumanalyzer_measurements/Spectrum Analyzer';
cfg = get_param(sablock,'ScopeConfiguration');

Enable Measurements Data

To obtain the measurements, set the Enabled property to true.

cfg.CursorMeasurements.Enabled = true;
cfg.ChannelMeasurements.Enabled = true;
cfg.DistortionMeasurements.Enabled = true;
cfg.PeakFinder.Enabled = true;

Simulate the Model

Run the model. The Spectrum Analyzer block compares the original spectrum with the filtered spectrum.

sim(model)

The panes at the bottom of the spectrum analyzer window display the measurements that you have enabled.

Use getMeasurementsData function

Use the getMeasurementsData function to obtain the measurements programmatically.

data = getMeasurementsData(cfg)

data =

  1x5 table

    SimulationTime    PeakFinder    CursorMeasurements    ChannelMeasurements    DistortionMeasurements
    ______________    __________    __________________    ___________________    ______________________

        9.9962        1x1 struct        1x1 struct            1x1 struct               1x1 struct      

The values shown in the measurement panels match the values shown in data. You can access the individual fields of data to obtain the various measurements programmatically.

Compare Peak Values

As an example, compare the peak values. Verify that the peak values obtained by data.PeakFinder match with the values in the spectrum analyzer window.

peakvalues = data.PeakFinder.Value
frequencieskHz = data.PeakFinder.Frequency/1000

peakvalues =

   26.8237
   26.3370
   -5.3604


frequencieskHz =

   15.0015
    1.0049
   12.2739

Input Arguments

scope — Spectrum Analyzer

object name | block configuration

Spectrum Analyzer you want to query, specified as one of the following:

• spectrumAnalyzer object

• SpectrumAnalyzerBlockConfiguration object for a Spectrum Analyzer block

Output Arguments

data — Measurements data

table

Measurements data, returned as a table. When you specify "all", the function returns a measurements table containing the following fields.

Field	Description
SimulationTime	Simulation time
PeakFinder	Peak finder data
CursorMeasurements	Cursor measurements data
ChannelMeasurements	Channel measurements data
DistortionMeasurements	Distortion measurements data
CCDFMeasurements (applies only for SpectrumAnalyzerConfiguration object)	CCDF measurements data

When you do not specify "all", the data table contains only the Spectrum Analyzer measurements currently in use.

Version History

Introduced in R2018b

R2024a: dsp.SpectrumAnalyzer System object warns

The dsp.SpectrumAnalyzer System object™ warns in R2024a. Use the spectrumAnalyzer object instead.

Update Code

No updates to your code are required except replacing instances of dsp.SpectrumAnalyzer with spectrumAnalyzer.

This table shows how the getMeasurementsData function typically uses the dsp.SpectrumAnalyzer System object and explains how to update existing code to use the spectrumAnalyzer object.

Discouraged Usage	Recommended Replacement
scope = dsp.SpectrumAnalyzer; scope.CursorMeasurements.Enable = true; scope.ChannelMeasurements.Enable = true; scope(randn(100000,1)) getMeasurementsData(scope)	scope = spectrumAnalyzer; scope.CursorMeasurements.Enabled = true; scope.ChannelMeasurements.Enabled = true; scope(randn(100000,1)) getMeasurementsData(scope)

R2022a: Support for dsp.SpectrumAnalyzer object will be removed

The getMeasurementsData function will stop supporting the dsp.SpectrumAnalyzer object in a future release. Use the spectrumAnalyzer object instead.