dsp.SpectrumAnalyzer

Display frequency spectrum of time-domain signals

Description

The Spectrum Analyzer System object™ displays the frequency spectrum of time-domain signals. This scope supports variable-size input, which allows the input frame size to change. Frame size is the first dimension of the input vector. The number of input channels must remain constant.

To display the spectra of signals in the Spectrum Analyzer:

  1. Create the dsp.SpectrumAnalyzer object and set its properties.

  2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects? (MATLAB).

Creation

Syntax

scope = dsp.SpectrumAnalyzer
scope = dsp.SpectrumAnalyzer(ports)
scope = dsp.SpectrumAnalyzer(Name,Value)

Description

scope = dsp.SpectrumAnalyzer creates a Spectrum Analyzer System object. This object displays the frequency spectrum of real- and complex-valued floating- and fixed-point signals.

scope = dsp.SpectrumAnalyzer(ports) creates a Spectrum Analyzer object and sets the NumInputPorts property to the value of ports.

scope = dsp.SpectrumAnalyzer(Name,Value) sets properties using one or more name-value pairs. Enclose each property name in single quotes.

Properties

expand all

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects (MATLAB).

Frequently Used

Number of input ports, specified as a positive integer. Each signal coming through a separate input becomes a separate channel in the scope. You must invoke the scope with the same number of inputs as the value of this property.

The domain of the input signal you want to visualize. If you visualize time-domain signals, the signal is transformed to the frequency spectrum based on the algorithm specified by the Method parameter.

UI Use

Open the Spectrum Settings. In the Main options section, set Input Domain.

Data Types: char | string

Specify the spectrum type to display.

"Power" — Power spectrum

"Power density" — Power spectral density. The power spectral density is the magnitude squared of the spectrum normalized to a bandwidth of 1 hertz.

"RMS" — Root mean square. The root-mean-square shows the square root of the sum of the squared means. This option is useful when viewing the frequency of voltage or current signals.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Main options section, set Type.

Data Types: char | string

Specify the spectrum type as one of "Spectrum", "Spectrogram", or "Spectrum and spectrogram".

  • "Spectrum" — shows the power spectrum.

  • "Spectrogram" — shows frequency content over time. Each line of the spectrogram is one periodogram. Time scrolls from the bottom to the top of the display. The most recent spectrogram update is at the bottom of the display.

  • "Spectrum and Spectrogram" — shows a dual view of a spectrum and spectrogram.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Main options section, set View.

Data Types: char | string

Specify the sample rate, in hertz, of the input signals as a finite numeric scalar.

UI Use

Open the Spectrum Settings. In the Main options section, set Sample rate (Hz).

Specify the spectrum estimation method as Welch or Filter bank.

Dependency

To enable this property, set InputDomain to "Time".

UI Use

Open the Spectrum Settings. In the Main options section, set Method.

Data Types: char | string

  • true — Compute and plot two-sided spectral estimates. When the input signal is complex-valued, you must set this property to true.

  • false — Compute and plot one-sided spectral estimates. If you set this property to false, then the input signal must be real-valued.

    When this property is false, Spectrum Analyzer uses power-folding. The y-axis values are twice the amplitude that they would be if this property were set to true, except at 0 and the Nyquist frequency. A one-sided power spectral density (PSD) contains the total power of the signal in the frequency interval from DC to half of the Nyquist rate. For more information, see pwelch.

UI Use

Open the Spectrum Settings. In the Trace options section, select Two-sided spectrum.

Data Types: logical

  • "Log" — displays the frequencies on the x-axis on a logarithmic scale. To use the "Log" setting, you must also set the PlotAsTwoSidedSpectrum property to false.

  • "Linear" — displays the frequencies on the x-axis on a linear scale. To use the "Linear" setting, you must also set the PlotAsTwoSidedSpectrum property to true.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Trace options section, set Scale.

Data Types: char | string

Advanced

  • "Full" - The Spectrum Analyzer computes and plots the spectrum over the entire Nyquist frequency interval.

  • "Span and center frequency" - The Spectrum Analyzer computes and plots the spectrum over the interval specified by the Span and CenterFrequency properties.

  • "Start and stop frequencies" - The Spectrum Analyzer computes and plots the spectrum over the interval specified by the StartFrequency and StopFrequency properties.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Main options section, select Full frequency span for "Full". Otherwise, clear the Full frequency span check box and choose between Span or FStart.

Data Types: char | string

Specify the frequency span, in hertz, over which the Spectrum Analyzer computes and plots the spectrum. The overall span, defined by this property and the CenterFrequency property, must fall within the Nyquist frequency interval.

Tunable: Yes

Dependency

To enable this property, set FrequencySpan to "Span and center frequency".

UI Use

Open the Spectrum Settings. In the Main options section, clear the Full frequency span check box and set Span.

Start of the frequency interval over which spectrum is computed, specified in hertz as a real scalar. The overall span, which is defined by this property and StopFrequency, must fall within the Nyquist frequency interval.

Tunable: Yes

Dependency

To enable this property, set FrequencySpan to "Start and stop frequencies".

UI Use

Open the Spectrum Settings. In the Main options section, clear the Full frequency span and change Span to FStart. Set FStart (Hz).

End of the frequency interval over which spectrum is computed, specified in hertz as a real scalar. The overall span, which is defined by this property and the StartFrequency property, must fall within the Nyquist frequency interval.

Tunable: Yes

Dependency

To enable this property, set FrequencySpan to "Start and stop frequencies".

UI Use

Open the Spectrum Settings. In the Main options section, clear the Full frequency span and change Span to FStart. Set FStop (Hz).

Specify in hertz the center frequency of the span over which the Spectrum Analyzer computes and plots the spectrum. The overall frequency span, defined by the Span and this property, must fall within the Nyquist frequency interval.

Tunable: Yes

Dependency

To enable this property, set FrequencySpan to "Span and center frequency".

UI Use

Open the Spectrum Settings. In the Main, clear Full frequency span and set CF (Hz).

Specify the frequency resolution method of the Spectrum Analyzer.

  • "RBW" - the RBWSource and RBW properties control the frequency resolution (in Hz) of the analyzer. The FFT length is the window length that results from achieving the specified RBW value or 1024, whichever is larger.

  • "WindowLength" - applies only when the Method property is set to "Welch". The WindowLength property controls the frequency resolution. You can control the number of FFT points only when the FrequencyResolutionMethod property is "WindowLength".

  • "NumFrequencyBands" - applies only when the Method property is set to "Filter Bank". The FFTLengthSource and FFTLength properties control the frequency resolution.

Tunable: Yes

Dependency

To enable this property, set InputDomain to "Time".

UI Use

Open the Spectrum Settings. In the Main options section, set the frequency resolution method by selecting the RBW (Hz) dropdown.

Data Types: char | string

Specify the source of the resolution bandwidth (RBW) as either "Auto" or "Property".

  • "Auto" — The Spectrum Analyzer adjusts the spectral estimation resolution to ensure that there are 1024 RBW intervals over the defined frequency span.

  • "Property" — Specify the resolution bandwidth directly using the RBW property.

Tunable: Yes

Dependency

To enable this property, set either:

UI Use

Open the Spectrum Settings. In the Main options section, set RBW (Hz).

Data Types: char | string

RBW controls the spectral resolution of Spectrum Analyzer. Specify the resolution bandwidth in hertz as a real positive scalar. You must specify a value to ensure that there are at least two RBW intervals over the specified frequency span. Thus, the ratio of the overall span to RBW must be greater than two:

spanRBW>2

You can specify the overall span in different ways based on how you set the FrequencySpan property.

Dependency

To enable, set:

UI Use

Open the Spectrum Settings. In the Main options section, set RBW (Hz).

Control the frequency resolution by specifying the window length, in samples used to compute the spectral estimates. The window length must be an integer scalar greater than 2.

Tunable: Yes

Dependencies

To enable this property, set:

UI Use

Open the Spectrum Settings. Change the RBW (Hz) dropdown to Window length.

  • "Auto" - sets the FFT length to the window length specified in the WindowLength property or 1024, whichever is larger.

  • "Property" - number of FFT points using the FFTLength property. FFTLength must be greater than WindowLength.

Tunable: Yes

Dependency

To enable this property, set FrequencyResolutionMethod to "WindowLength".

UI Use

Open the Spectrum Settings. In the Main options section, next to the RBW (Hz) option, enter a number or select Auto.

Data Types: char | string

Specify the length of the FFT that the Spectrum Analyzer uses to compute spectral estimates.

If FrequencyResolutionMethod is "RBW", the FFT length is set as the window length required to achieve the specified resolution bandwidth value or 1024, whichever is larger.

Tunable: Yes

Dependencies

To use this property, the following must be true:

UI Use

Open the Spectrum Settings. In the Main options section, next to the RBW (Hz) option, enter a number or select Auto.

Specify the number of filter taps or coefficients for each frequency band. This number must be a positive even integer. This value corresponds to the number of filter coefficients per polyphase branch. The total number of filter coefficients is equal to NumTapsPerBand + FFTLength.

Dependency

To enable this property, set Method to "Filter Bank"

UI Use

Open the Spectrum Settings. In the Main options section, set Taps per band.

  • "Auto" — The frequency vector is calculated from the length of the input. See Frequency Vector.

  • "Property" — Enter a custom vector as the frequency vector.

Dependency

To enable this property, set InputDomain to "Frequency".

UI Use

Open the Spectrum Settings. In the Frequency input options section, set Frequency (Hz).

Data Types: char | string

Set the frequency vector that determines the x-axis of the display. The vector must be monotonically increasing and of the same size as the input frame size.

Dependency

To enable this property, set FrequencyVectorSource to "Property".

UI Use

Open the Spectrum Settings. In the Frequency input options section, set Frequency (Hz).

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

The percentage overlap between the previous and current buffered data segments, specified as a real, scalar value. The overlap creates a window segment that is used to compute a spectral estimate. The value must be greater than or equal to zero and less than 100.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Window options section, set Overlap (%).

Specify a window function for the spectral estimator. The following table shows preset windows. For more information, follow the link to the corresponding function reference in the Signal Processing Toolbox™ documentation.

Window OptionCorresponding Signal Processing Toolbox Function
"Rectangular"rectwin
"Chebyshev"chebwin
"Flat Top"flattopwin
"Hamming"hamming
"Hann"hann
"Kaiser"kaiser
"Blackman-Harris"blackmanharris

To set your own spectral estimation window, set this property to "Custom" and specify a custom window function in the CustomWindow property.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Window options section, set Window.

Data Types: char | string

Specify a custom window function as a character array or string. The custom window function name must be on the MATLAB path. This property is useful if you want to customize the window using additional properties available with the Signal Processing Toolbox version of the window function.

Tunable: Yes

Example

Define and use a custom window function.

function w = my_hann(L)
    w = hann(L, 'periodic')
end

scope.Window = 'Custom';
scope.CustomWindow = 'my_hann'

Dependency

To use this property, set Window to "Custom".

UI Use

Open the Spectrum Settings. In the Window options section, in the Window option box, enter a custom window function name.

Data Types: char | string

The window sidelobe attenuation, in decibels (dB). The value must be greater than or equal to 45.

Tunable: Yes

Dependency

To enable this property, set Window to "Chebyshev" or "Kaiser".

UI Use

Open the Spectrum Settings. In the Window options section, set Attenuation (dB).

Select the units of the frequency-domain input. This property allows the Spectrum Analyzer to scale frequency data if you choose a different display unit with the Units property.

Dependency

This option is only available when InputDomain is set to Frequency.

UI Use

Open the Spectrum Settings. In the Frequency input options section, set Input units.

Data Types: char | string

Specify the units in which the Spectrum Analyzer displays power values.

Tunable: Yes

Dependency

The available spectrum units depend on the value of SpectrumType.

InputDomainSpectrumTypeAllowed SpectrumUnits
TimePower or Power density"dBFS", "dBm", "dBW", "Watts"
RMS"Vrms", "dBV"
Frequency"dBm", "dBV", "dBW", "Vrms", "Watts",

UI Use

Open the Spectrum Settings. In the Trace options section, set Units.

Data Types: char | string

Specify the source of the dBFS scaling factor as either "Auto" or "Property".

  • "Auto" - The Spectrum Analyzer adjusts the scaling factor based on the input data.

  • "Property" - Specify the full-scale scaling factor using the FullScale property.

Dependency

To enable this property, set SpectrumUnits to "dBFS".

UI Use

Open the Spectrum Settings. In the Trace options section, set Full scale to Auto or enter a number.

Data Types: char | string

Specify a real positive scalar for the dBFS full scale.

Tunable: Yes

Dependency

To enable this option set:

UI Use

Open the Spectrum Settings. In the Trace options section, set Full scale to Auto or enter a number.

Specify the smoothing method as:

  • Running — Running average of the last n samples. Use the SpectralAverages property to specify n.

  • Exponential — Weighted average of samples. Use the ForgettingFactor property to specify the weighted forgetting factor.

For more information about the averaging methods, see Averaging Method.

Dependency

To enable this property, set ViewType to "Spectrum" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Trace options section, set Averaging method.

Data Types: char | string

The Spectrum Analyzer computes the current power spectrum estimate by computing a running average of the last N power spectrum estimates. This property defines N.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrum".

Dependency

This property applies only when the AveragingMethod is "Running".

UI Use

Open the Spectrum Settings. In the Trace options section, set Averages.

Specify the exponential weighting as a scalar value greater than 0 and less than or equal to 1.

Dependency

This property applies only when the AveragingMethod is "Exponential".

UI Use

Open the Spectrum Settings. In the Trace options section, set Forgetting factor.

The load the scope uses as a reference to compute power levels.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Trace options section, set Reference load.

  • Scalar — Apply the same frequency offset to all channels, specified in hertz as a character vector.

  • Vector — apply a specific frequency offset for each channel, specify a vector of frequencies. The vector length must be equal to number of input channels.

    The frequency-axis values are offset by the values specified in this property. The overall span must fall within the Nyquist frequency interval. You can control the overall span in different ways based on how you set the FrequencySpan property.

Tunable: Yes

UI Use

Open the Spectrum Settings. In the Trace options section, set Offset (Hz).

Spectrogram

Specify the channel for which the spectrogram is plotted, as a real, positive scalar integer in the range [1 N], where N is the number of input channels.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrogram" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Spectrogram options section, select a Channel.

Specify the source for the time resolution of each spectrogram line as either "Auto" or "Property". The TimeResolution property shows the time resolution for the different frequency resolution methods and time resolution properties.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrogram" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Spectrogram options section, set Time res (s).

Data Types: char | string

Specify the time resolution of each spectrogram line as a positive scalar, expressed in seconds.

The time resolution value is determined based on frequency resolution method, the RBW setting, and the time resolution setting.

MethodFrequency Resolution MethodFrequency Resolution SettingTime Resolution SettingResulting Time Resolution in Seconds
Welch or Filter BankRBW (Hz)AutoAuto1/RBW
Welch or Filter BankRBW (Hz)AutoManually enteredTime Resolution
Welch or Filter BankRBW (Hz)Manually enteredAuto1/RBW
Welch or Filter BankRBW (Hz)Manually enteredManually enteredMust be equal to or greater than the minimum attainable time resolution, 1/RBW. Several spectral estimates are combined into one spectrogram line to obtain the desired time resolution. Interpolation is used to obtain time resolution values that are not integer multiples of 1/RBW.
WelchWindow lengthAuto1/RBW
WelchWindow lengthManually enteredMust be equal to or greater than the minimum attainable time resolution. Several spectral estimates are combined into one spectrogram line to obtain the desired time resolution. Interpolation is used to obtain time resolution values that are not integer multiples of 1/RBW.
Filter BankNumber of frequency bandsAuto1/RBW
Filter BankNumber of frequency bandsManually enteredMust be equal to or greater than the minimum attainable time resolution, 1/RBW.

Tunable: Yes

Dependency

To enable this property, set:

UI Use

Open the Spectrum Settings. In the Spectrogram options section, in the Time res (s) box, enter a number.

Specify the source for the time span of the spectrogram as either "Auto" or "Property". If you set this property to "Auto", the spectrogram displays 100 spectrogram lines at any given time. If you set this property to "Property", the spectrogram uses the time duration you specify in seconds in the TimeSpan property.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrogram" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Spectrogram options section, set Time span (s).

Data Types: char | string

Specify the time span of the spectrogram display in seconds. You must set the time span to be at least twice as large as the duration of the number of samples required for a spectral update.

Tunable: Yes

Dependency

To enable this property, set:

UI Use

Open the Spectrum Settings. In the Spectrogram options section, in the Time span (s) box, enter a number.

Measurements

Channel for which the measurements are obtained, specified as a real, positive integer greater than 0 and less than or equal to 100. The maximum number you can specify is the number of channels (columns) in the input signal.

Tunable: Yes

UI Use

Click on Tools > Measurements and open the Trace Selection settings.

Data Types: double

Specify whether to display upper and lower spectral mask lines on a spectrum plot. This property uses SpectralMaskSpecification properties to enable and configure the spectral masks. The SpectralMaskSpecification properties are:

  • EnabledMasks — Masks to enable, specified as a character vector or string. Valid values are "None", "Upper", "Lower", or "Upper and lower".

    Default: "None"

  • UpperMask — Upper limit spectral mask, specified as a scalar or two-column matrix. If UpperMask is a scalar, the upper limit mask uses the power value of the scalar for all frequency values applicable to the Spectrum Analyzer. If UpperMask is a matrix, the first column contains the frequency values (Hz), which correspond to the x-axis values. The second column contains the power values, which correspond to the associated y-axis values. To apply offsets to the power and frequency values, use the ReferenceLevel and MaskFrequencyOffset property values, respectively.

    Default: Inf

  • LowerMask — Lower limit spectral mask, specified as a scalar or two-column matrix. If LowerMask is a scalar, the lower limit mask uses the power value of the scalar for all frequency values applicable to the Spectrum Analyzer. If LowerMask is a matrix, the first column contains the frequency values (Hz), which correspond to the x-axis values. The second column contains the power values, which correspond to the associated y-axis values. To apply offsets to the power and frequency values, use the ReferenceLevel and MaskFrequencyOffset property values, respectively.

    Default: -Inf

  • ReferenceLevel — Reference level for mask power values, specified as either "Custom" or "Spectrum peak". When ReferenceLevel is "Custom", the CustomReferenceLevel property value is used as the reference to the power values, in dBr, in the UpperMask and LowerMask properties. When ReferenceLevel is "Spectrum peak", the peak value of the current spectrum of the SelectedChannel is used.

    Default: "Custom"

  • CustomReferenceLevel — Custom reference level, specified as a real value, in the same units as the power units. The reference level is the value to which the power values in the UpperMask and LowerMask properties are referenced. This property applies when ReferenceLevel is set to "Custom". This property uses the same units as the PowerUnits property of the Spectrum Analyzer.

    Default: 0

  • SelectedChannel — Input channel with peak spectrum to use as the mask reference level, specified as an integer. This property applies when ReferenceLevel is set to "Spectrum peak".

    Default: 1

  • MaskFrequencyOffset — Frequency offset, specified as a finite, numeric scalar. Frequency offset is the amount of offset to apply to frequency values in the UpperMask and LowerMask properties.

    Default: 0

All SpectralMaskSpecification properties are tunable.

Masks are overlaid on the spectrum. If the mask is green, the signal is passing the mask limitations. If the mask is red, the signal is failing the mask limits.

You can check the status of the spectral mask using any of these methods:

  • To modify the spectral mask and see the spectral mask status, in the scope toolbar, select the spectral mask button, . In the Spectral Mask pane that opens, you can modify the masks and see details about what percentage of the time the mask is succeeding, which mask is failing, how many times the mask failed, and which channels are causing the failure.

  • To get the current status of the spectral masks, call the function getSpectralMaskStatus.

  • To perform an action every time the mask fails, use the MaskTestFailed event. To trigger a function when the mask fails, create a listener to the MaskTestFailed event and define a callback function to trigger. For more details about using events, see Events (MATLAB).

Tunable: Yes

UI Use

Open the Spectral Mask pane and modify the Settings options.

Enable peak finder to compute and display the largest calculated peak values. The PeakFinder property uses the PeakFinderSpecification properties.

The PeakFinderSpecification properties are:

  • MinHeight –– Level above which peaks are detected, specified as a scalar value.

    Default: -Inf

  • NumPeaks –– Maximum number of peaks to show, specified as a positive integer scalar less than 100.

    Default: 3

  • MinDistance –– Minimum number of samples between adjacent peaks, specified as a positive real scalar.

    Default: 1

  • Threshold –– Minimum height difference between peak and its neighboring samples, specified as a nonnegative real scalar.

    Default: 0

  • LabelFormat –– Coordinates to display next to the calculated peak value, specified as a character vector or a string scalar. Valid values are "X", "Y", or "X + Y".

    Default: "X + Y"

  • Enable –– Set this property to true to enable peak finder measurements. Valid values are true or false.

    Default: false

All PeakFinderSpecification properties are tunable.

Tunable: Yes

UI Use

Open the Peak Finder pane () and modify the Settings options.

Enable cursor measurements to display screen or waveform cursors. The CursorMeasurements property uses the CursorMeasurementsSpecification properties.

The CursorMeasurementsSpecification properties are:

  • Type –– Type of the display cursors, specified as either "Screen cursors" or "Waveform cursors".

    Default: "Waveform cursors"

  • ShowHorizontal –– Set this property to true to show the horizontal screen cursors. This property applies when you set the Type property to "Screen cursors".

    Default: true

  • ShowVertical –– Set this property to true to show the vertical screen cursors. This property applies when you set the Type property to "Screen cursors".

    Default: true

  • Cursor1TraceSource –– Specify the waveform cursor 1 source as a positive real scalar. This property applies when you set the Type property to "Waveform cursors".

    Default: 1

  • Cursor2TraceSource –– Specify the waveform cursor 2 source as a positive real scalar. This property applies when you set the Type property to "Waveform cursors".

    Default: 1

  • LockSpacing –– Lock spacing between cursors, specified as a logical scalar.

    Default: false

  • SnapToData –– Snap cursors to data, specified as a logical scalar.

    Default: true

  • XLocation –– x-coordinates of the cursors, specified as a real vector of length equal to 2.

    Default: [-2500 2500]

  • YLocation –– y-coordinates of the cursors, specified as a real vector of length equal to 2. This property applies when you set the Type property to "Screen cursors".

    Default: [-55 5]

  • Enable –– Set this property to true to enable cursor measurements. Valid values are true or false.

    Default: false

All CursorMeasurementsSpecification properties are tunable.

UI Use

Open the Cursor Measurements pane () and modify the Settings options.

Enable channel measurements to compute and display the occupied bandwidth or adjacent channel power ratio. The ChannelMeasurements property uses the ChannelMeasurementsSpecification properties.

The ChannelMeasurementsSpecification properties are:

  • Algorithm –– Type of measurement data to display, specified as either "Occupied BW" or "ACPR".

    Default: "Occupied BW"

  • FrequencySpan –– Frequency span mode, specified as either "Span and center frequency" or "Start and stop frequencies"

    Default: "Span and center frequency"

  • Span –– Frequency span over which the channel measurements are computed, specified as a real, positive scalar in Hz. This property applies when you set the FrequencySpan property to "Span and center frequency".

    Default: 2000 Hz

  • CenterFrequency –– Center frequency of the span over which the channel measurements are computed, specified as a real scalar in Hz. This property applies when you set the FrequencySpan property to "Span and center frequency".

    Default: 0 Hz

  • StartFrequency –– Start frequency over which the channel measurements are computed, specified as a real scalar in Hz. This property applies when you set the FrequencySpan property to "Start and stop frequencies".

    Default: -1000 Hz

  • StopFrequency –– Stop frequency over which the channel measurements are computed, specified as a real scalar in Hz. This property applies when you set the FrequencySpan property to "Start and stop frequencies".

    Default: 1000 Hz

  • PercentOccupiedBW –– Percent of power over which to compute the occupied bandwidth, specified as a positive real scalar. This property applies when you set the Algorithm property to "Occupied BW".

    Default: 99

  • NumOffsets –– Number of adjacent channel pairs, specified as a real, positive integer. This property applies when you set the Algorithm property to "ACPR".

    Default: 2

  • AdjacentBW –– Adjacent channel bandwidth, specified as a real, positive scalar. This property applies when you set the Algorithm property to "ACPR".

    Default: 1000

  • FilterShape –– Filter shape for both main and adjacent channels, specified as "None", "Gaussian", or "RRC". This property applies when you set the Algorithm property to "ACPR".

    Default: "None"

  • FilterCoeff –– Channel filter coefficient, specified as a real scalar between 0 and 1. This property applies when you set the Algorithm property to "ACPR" and the FilterShape property to either "Gaussian" or "RRC".

    Default: 0.5

  • ACPROffsets –– Frequency of the adjacent channel relative to the center frequency of the main channel, specified as a real vector of length equal to the number of offset pairs specified in NumOffsets. This property applies when you set the Algorithm property to "ACPR".

    Default: [2000 3500]

  • Enable –– Set this property to true to enable channel measurements. Valid values are true or false.

    Default: false

All ChannelMeasurementsSpecification properties are tunable.

UI Use

Open the Channel Measurements pane () and modify the Measurement and Channel Settings options.

Enable distortion measurements to compute and display the harmonic distortion and intermodulation distortion. The DistortionMeasurements property uses the DistortionMeasurementsSpecification properties.

The DistortionMeasurementsSpecification properties are:

  • Algorithm –– Type of measurement data to display, specified as either "Harmonic" or "Intermodulation".

    Default: "Harmonic"

  • NumHarmonics –– Number of harmonics to measure, specified as a real, positive integer. This property applies when you set the Algorithm to "Harmonic".

    Default: 6

  • Enable –– Set this property to true to enable distortion measurements.

    Default: false

All DistortionMeasurementsSpecification properties are tunable.

UI Use

Open the Distortion Measurements pane () and modify the Distortion and Harmonics options.

Enable CCDF measurements to display the probability of the input signal's instantaneous power being a certain amount of dB above the signal's average power. The CCDFMeasurements property uses the CCDFMeasurementsSpecification properties.

The CCDFMeasurementsSpecification properties are:

  • PlotGaussianReference –– Show a reference CCDF curve of additive white Gaussian noise. Set this property to true to plot a reference CCDF curve.

    Default: false

  • Enable –– Set this property to true to enable CCDF measurements. Valid values are true or false.

    Default: false

All CCDFMeasurementsSpecification properties are tunable.

UI Use

Open the CCDF Measurements pane () and enable the Plot Gaussian reference option.

Visualization

Title of the scope window.

Tunable: Yes

Data Types: char | string

Spectrum Analyzer window position in pixels, specified by the size and location of the scope window as a four-element double vector of the form [left bottom width height]. You can place the scope window in a specific position on your screen by modifying the values to this property.

By default, the window appears in the center of your screen with a width of 800 pixels and height of 450 pixels. The exact center coordinates depend on your screen resolution.

Tunable: Yes

Specify the type of plot to use for displaying normal traces as either "Line" or "Stem". Normal traces are traces that display free-running spectral estimates.

Tunable: Yes

Dependencies

To enable this property, set:

UI Use

Open the Style properties and set Plot type.

Data Types: char | string

Set this property to false to remove the display of the normal traces. These traces display the free-running spectral estimates. Even when the traces are removed from the display, the Spectrum Analyzer continues its spectral computations.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrum" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Trace options section, select Normal trace.

Data Types: logical

To compute and plot the maximum-hold spectrum of each input channel, set this property to true. The maximum-hold spectrum at each frequency bin is computed by keeping the maximum value of all the power spectrum estimates. When you toggle this property, the Spectrum Analyzer resets its maximum-hold computations.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrum" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Trace options section, select Max-hold trace.

Data Types: logical

To compute and plot the minimum-hold spectrum of each input channel, set this property to true. The minimum-hold spectrum at each frequency bin is computed by keeping the minimum value of all the power spectrum estimates. When you toggle this property, the Spectrum Analyzer resets its minimum-hold computations.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrum" or "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. In the Trace options section, select Min-hold trace.

Data Types: logical

The simulation speed is faster when this property is set to true.

  • true — the scope logs data for later use and updates the display at fixed intervals of time. Data occurring between these fixed intervals might not be plotted.

  • false — the scope updates every time it computes the power spectrum. Use the false setting when you do not want to miss any spectral updates at the expense of slower simulation speed.

Tunable: Yes

UI Use

Select Playback > Reduce plot rate to improve performance.

Specify the display title as a character vector or string.

Tunable: Yes

UI Use

Open the Configuration Properties. Set Title.

Data Types: char | string

Specify the text for the scope to display to the left of the y-axis.

Regardless of this property, Spectrum Analyzer always displays power units as one of the SpectrumUnits values.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrum" or "Spectrum and spectrogram".

UI Use

Open the Configuration Properties. Set Y-label.

Data Types: char | string

To show a legend with the input names, set this property to true.

From the legend, you can control which signals are visible. This control is equivalent to changing the visibility in the Style dialog box. In the scope legend, click a signal name to hide the signal in the scope. To show the signal, click the signal name again. To show only one signal, right-click the signal name. To show all signals, press Esc.

Note

The legend only shows the first 20 signals. Any additional signals cannot be viewed or controlled from the legend.

Tunable: Yes

UI Use

Open the Configuration Properties. On the Display tab, select Show legend.

Data Types: logical

Specify the input channel names as a cell array of character vectors. The names appear in the legend, Style dialog box, and Measurements panels. If you do not specify names, the channels are labeled as Channel 1, Channel 2, etc.

Tunable: Yes

Dependency

To see channel names, set ShowLegend to true.

UI Use

On the legend, double-click the channel name.

Data Types: char

Set this property to true to show gridlines on the plot.

Tunable: Yes

UI Use

Open the Configuration Properties. On the Display tab, set Show grid.

Data Types: logical

Specify the y-axis limits as a two-element numeric vector, [ymin ymax].

Example: scope.YLimits = [-10,20]

Tunable: Yes

Dependencies

  • To enable this property, set the ViewType property to "Spectrum" or "Spectrum and spectrogram".

  • The units directly depend upon the SpectrumUnits property.

UI Use

Open the Configuration Properties. Set Y-limits (maximum) and Y-limits (minimum).

Control the color limits of the spectrogram using a two-element numeric vector, [colorMin colorMax].

Example: scope.ColorLimits = [-10,20]

Dependencies

  • To enable this property, set the ViewType property to "Spectrogram" or "Spectrum and spectrogram".

  • The units directly depend upon the SpectrumUnits property.

UI Use

Open the Configuration Properties. Set Color-limits (minimum) and Color-limits (maximum).

Specify when the scope automatically scales the axes. Valid values are:

  • "Auto" — The scope scales the axes as-needed to fit the data, both during and after simulation.

  • "Manual" — The scope does not scale the axes automatically.

  • "OnceAtStop" — The scope scales the axes when the simulation stops.

  • "Updates" — The scope scales the axes once after 10 updates.

UI Use

Select Tools > Axes Scaling.

Data Types: char | string

Specify the layout type as "Horizontal" or "Vertical". A vertical layout stacks the spectrum above the spectrogram. A horizontal layout puts the two views side-by-side.

Tunable: Yes

Dependency

To enable this property, set ViewType to "Spectrum and spectrogram".

UI Use

Open the Spectrum Settings. Set Axes layout.

Data Types: char | string

Usage

For versions earlier than R2016b, use the step function to run the System object algorithm. The arguments to step are the object you created, followed by the arguments shown in this section.

For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

Syntax

scope(signal)
scope(signal1,signal2,...,signalN)

Description

scope(signal) updates the spectrum of the signal in the spectrum analyzer.

scope(signal1,signal2,...,signalN) displays multiple signals in the spectrum analyzer. The signals must have the same frame length, but can vary in number of channels. You must set the NumInputPorts property to enable multiple input signals.

Input Arguments

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Specify one or more input signals to visualize in the dsp.SpectrumAnalyzer. Signals can have a different number of channels, but must have the same frame length.

Example: scope(signal1, signal2)

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | fi

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

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getSpectralMaskStatusGet test results of current spectral mask
getSpectrumDataSave spectrum data shown in spectrum analyzer
isNewDataReadyCheck spectrum analyzer for new data
getMeasurementsDataGet the current measurement data displayed on the spectrum analyzer
showDisplay scope window
hideHide scope window
isVisibleDetermine visibility of scope
stepRun System object algorithm
releaseRelease resources and allow changes to System object property values and input characteristics
resetReset internal states of System object

Examples

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View a one-sided power spectrum made from the sum of fixed real sine waves with different amplitudes and frequencies.

Fs = 100e6;  % Sampling frequency
fSz = 5000;  % Frame size

sin1 = dsp.SineWave(1e0,  5e6,0,'SamplesPerFrame',fSz,'SampleRate',Fs);
sin2 = dsp.SineWave(1e-1,15e6,0,'SamplesPerFrame',fSz,'SampleRate',Fs);
sin3 = dsp.SineWave(1e-2,25e6,0,'SamplesPerFrame',fSz,'SampleRate',Fs);
sin4 = dsp.SineWave(1e-3,35e6,0,'SamplesPerFrame',fSz,'SampleRate',Fs);
sin5 = dsp.SineWave(1e-4,45e6,0,'SamplesPerFrame',fSz,'SampleRate',Fs);

scope = dsp.SpectrumAnalyzer;
scope.SampleRate = Fs;
scope.SpectralAverages = 1;
scope.PlotAsTwoSidedSpectrum = false;
scope.RBWSource = 'Auto';
scope.PowerUnits = 'dBW';
for idx = 1:1e2 
     y1 = sin1();
     y2 = sin2();
     y3 = sin3();
     y4 = sin4();
     y5 = sin5();
     scope(y1+y2+y3+y4+y5+0.0001*randn(fSz,1));
end

Run the release method to let property values and input characteristics change. The scope automatically scales the axes.

release(scope)

Run the clear function to close the Spectrum Analyzer window.

clear('scope');

This example shows the spectrogram for a chirp signal with added random noise.

Fs = 233e3;
frameSize = 20e3;
chirp = dsp.Chirp('SampleRate',Fs,...
  'SamplesPerFrame',frameSize,...
  'InitialFrequency',11e3,...
  'TargetFrequency',11e3+55e3);

scope = dsp.SpectrumAnalyzer('SampleRate',Fs);
scope.ViewType = 'Spectrogram';
scope.RBWSource = 'Property';
scope.RBW = 500;
scope.TimeSpanSource = 'Property';
scope.TimeSpan = 2;
scope.PlotAsTwoSidedSpectrum = false;

for idx = 1:50
  y = chirp()+ 0.05*randn(frameSize,1);
  scope(y);
end

release(scope)

View a two-sided power spectrum of a sine wave with noise on the Spectrum Analyzer.

sin = dsp.SineWave('Frequency',100,'SampleRate',1000);
sin.SamplesPerFrame = 1000;
scope = dsp.SpectrumAnalyzer('SampleRate',sin.SampleRate);
for ii = 1:250
  x = sin() + 0.05*randn(1000,1);
  scope(x);
end

Run the release method to change property values and input characteristics. The scope automatically scales the axes. It updates the display one more time if any data is in the internal buffer.

release(scope);

Run the MATLAB clear function to close the Spectrum Analyzer window.

clear('scope');

Use the Spectrum Analyzer to display frequency input from spectral estimates of sinusoids embedded in white Gaussian noise.

Initialization

Initialize two dsp.SpectrumEstimator objects to display. Set one object to use the Welch-based spectral estimation technique with a Hann window, set the other object use a filter bank estimation. Specify a noisy sine wave input signal with four sinusoids at 0.16, 0.2, 0.205, and 0.25 cycles/sample. View the spectral estimate using a third object, a spectrum analyzer, set to process frequency input.

FrameSize = 420;
Fs = 1;
Frequency = [0.16 0.2 0.205 0.25];
sinegen = dsp.SineWave('SampleRate',Fs,'SamplesPerFrame',FrameSize,...
    'Frequency',Frequency,'Amplitude',[2e-5 1  0.05  0.5]);
NoiseVar = 1e-10;
numAvgs = 8;

hannEstimator = dsp.SpectrumEstimator('PowerUnits','dBm',...
    'Window','Hann','FrequencyRange','onesided',...
    'SpectralAverages',numAvgs,'SampleRate',Fs);

filterBankEstimator = dsp.SpectrumEstimator('PowerUnits','dBm',...
    'Method','Filter bank','FrequencyRange','onesided',...
    'SpectralAverages',numAvgs,'SampleRate',Fs);

spectrumPlotter = dsp.SpectrumAnalyzer('InputDomain','Frequency',...
    'SampleRate',Fs/FrameSize,...
    'SpectrumUnits','dBm','YLimits',[-120,40],...
    'PlotAsTwoSidedSpectrum',false,...
    'ChannelNames',{'Hann window','Filter bank'},'ShowLegend',true);

Streaming

Stream the input. Compare the spectral estimates in the spectrum analyzer.

for i = 1:1000
    x = sum(sinegen(),2) + sqrt(NoiseVar)*randn(FrameSize,1);
    Pse_hann = hannEstimator(x);
    Pfb = filterBankEstimator(x);
    spectrumPlotter([Pse_hann,Pfb])
end

Compute and display the power spectrum of a noisy sinusoidal input signal using the dsp.SpectrumAnalyzer System object. Measure the peaks, cursor placements, adjacent channel power ratio, distortion, and CCDF values in the spectrum by enabling the following properties:

  • PeakFinder

  • CursorMeasurements

  • ChannelMeasurements

  • DistortionMeasurements

  • CCDFMeasurements

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 dsp.SpectrumAnalyzer System 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 = dsp.SpectrumAnalyzer('SampleRate',Fs,'Method','Filter bank',...
    'SpectrumType','Power','PlotAsTwoSidedSpectrum',false,...
    'ChannelNames',{'Power spectrum of the input'},'YLimits',[-120 40],'ShowLegend',true);

Enable Measurements Data

To obtain the measurements, set the Enable property of the measurements to true.

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

Use getMeasurementsData

Stream in the noisy sine wave input signal and estimate the power spectrum of the signal using the spectrum analyzer. Measure the characteristics of the spectrum. Use the getMeasurementsData function to obtain these measurements programmatically. The isNewDataReady function indicates when there is new spectrum data. The measured data is stored 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 right side of the spectrum analyzer shows the enabled measurement panes. The values shown in these panes match with the values shown 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

Peak values are obtained by the PeakFinder property. Verify that the peak values obtained in the last time step of data match the values shown on the spectrum analyzer plot.

peakvalues = data.PeakFinder(end).Value 
peakvalues = 3×1

   26.9850
   24.1735
  -52.3506

frequencieskHz = data.PeakFinder(end).Frequency/1000
frequencieskHz = 3×1

    4.9957
    0.9905
    7.8166

Tips

  • To close the scope window and clear its associated data, use the MATLAB® clear function.

  • To hide or show the scope window, use the hide and show functions.

  • Use the MATLAB mcc function to compile code containing a Spectrum Analyzer.

    You cannot open Spectrum Analyzer configuration dialog boxes if you have more than one compiled component in your application.

Algorithms

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Extended Capabilities

Introduced in R2012b