Spectrum Analyzer
Display frequency spectrum
Libraries:
DSP System Toolbox /
Sinks
DSP System Toolbox HDL Support /
Sinks
Description
The Spectrum Analyzer block, referred to here as the scope, displays frequencydomain signals and the frequency spectrum of timedomain signals. The scope shows the spectrum view and the spectrogram view. The block algorithm performs spectral estimation using the filter bank method and Welch's method of averaged modified periodograms. You can customize the spectrum analyzer display to show the data and the measurement information that you need. For more details, see Algorithms.
You can use the Spectrum Analyzer block in models running in
Normal
or Accelerator
simulation modes. You can also use the Spectrum Analyzer block in models
running in Rapid Accelerator
or
External
simulation modes with some limitations.
You can use the Spectrum Analyzer block inside all subsystems and conditional subsystems. Conditional subsystems include enabled subsystems, triggered subsystems, enabled and triggered subsystems, and functioncall subsystems. See Conditionally Executed Subsystems Overview (Simulink) for more information.
Measurements
Cursor Measurements — Measure signal values using vertical and horizontal cursors.
Peak Finder Measurements — Find maxima and show the xaxis values at which they occur.
Channel Measurements — Measure the occupied bandwidth or adjacent channel power ratio (ACPR).
Distortion Measurements — Measure harmonic distortion and intermodulation distortion.
Spectral Mask — Visualize spectrum limits and compare spectrum values to specification values.
Programmatic Control
You can configure and display the Spectrum Analyzer settings from the command line
with the SpectrumAnalyzerConfiguration
object.
Examples
Display Frequency Input on Spectrum Analyzer
This example shows how to visualize frequency input signals with the Spectrum Analyzer block.
To visualize frequencydomain input signals using a Spectrum Analyzer block, in the Estimation tab of the Spectrum Analyzer toolstrip, set Input Domain to Frequency
. In the Spectrum tab, clear the TwoSided Spectrum parameter.
Run the model. You can see two peaks. To measure the peaks, enable Peak Finder in the Measurements tab.
Display VariableSize Input Signals on Spectrum Analyzer
Decimate a sinusoidal signal by varying the decimation factor using the Variable FIR Decimation block. You can vary the decimation factor in the block dialog box or through an input port while the simulation is running.
Open and Inspect Model
Open the DisplayVariableSizeSignalonSpectrumAnalyzer
model by clicking the Open Model button.
The input signal in the model is a sum of two sine waves with the frequencies of 1 kHz and 10 kHz, sample time of 1/44100 s, and contains 256 samples per frame. The Random Source block adds zeromean white Gaussian noise with a variance of 0.05 to the sum of sine waves.
Pass this signal through the Variable FIR Decimation block. The Maximum decimation factor parameter in the block is set to 24. You can specify the decimation factor through the input port and vary it using the Manual Switch block. The output of the Variable FIR Decimation block is a variablesize signal whose frame size varies according to the decimation factor that you specify.
Run Model
Visualize the spectrum of the decimated signal in the spectrum analyzer. The sample rate of the spectrum analyzer updates based on the frame size of the signal and the sample rate of the signal.
When you set the decimation factor to 2, the output frame size is half the input frame size, and the spectrum analyzer uses a sample rate of 44100/2 or 22.05 kHz.
While the simulation is running, change the decimation factor to 4. You can see that the sample rate of the spectrum analyzer adjusts to 44100/4 or 11.025 kHz. The tone at 1 kHz remains the same while the tone at 10 kHz is no longer visible in the spectrum analyzer since the span of the spectrum is now [0 Fs/2] = [0 5.5125 kHz].
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 = 26.8843 26.2215 3.8908 frequencieskHz = 15.0015 1.0049 16.2073
Ports
Input
Signal — Signals to visualize
scalar  vector  matrix  array
Connect the signals you want to visualize. You can have up to 96 input ports. Input signals must have these characteristics:
Signal Domain — Frequency or time signals.
Type — Discrete signals.
Data type — Any data type that Simulink supports. See Data Types Supported by Simulink (Simulink).
Dimension — One dimensional (vector), two dimensional (matrix), or multidimensional (array) signals. Input signal must have a fixed number of channels. See Signal Dimensions (Simulink) and Determine Signal Dimensions (Simulink).
The Spectrum Analyzer block supports variablesize input signals, that is, the frame size of the signals can change during simulation. When the signal frame size changes, the sample rate the scopes uses changes accordingly, which in turn updates the frequency span of the spectrum display. For an example that shows this behavior, see Display VariableSize Input Signals on Spectrum Analyzer.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 fixed point
Complex Number Support: Yes
Frequency — Frequencies in Hz
column vector
Specify the frequencies in Hz. The frequency vector must be a finite, monotonically increasing, column vector with two or more elements. The number of frequency vector points must be equal to the input frame size. You can also specify the frequencies using the Frequency (Hz) parameter on the Estimation tab.
Dependency
To enable this port, set the:
Input Domain parameter on the Estimation tab to
Frequency
.Frequency (Hz) parameter on the Estimation tab to
Input port
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 Boolean
 fixed point
RBW — RBW Value
positive scalar
Specify the resolution bandwidth in Hz through this port. RBW defines the smallest positive frequency that can be resolved by the scope. You can also specify the RBW value using the RBW (Hz) parameter on the Analyzer tab.
Dependency
To enable this port, set the RBW (Hz) parameter
on the Analyzer tab to Input
port
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 Boolean
 fixed point
VBW — VBW Value
positive scalar
Specify the video bandwidth in Hz through this port. Video bandwidth is the bandwidth of the lowpass filter that the scope uses to average or smooth the noise in the signal before displaying it. You can also specify the VBW value using the VBW (Hz) parameter on the Estimation tab.
Dependency
To enable this port, set the:
Input Domain parameter on the Estimation tab to
Time
.Averaging Method parameter on the Estimation tab to
VBW
.VBW (Hz) parameter on the Estimation tab to
Input port
.
Data Types: single
 double
 int8
 int16
 int32
 int64
 uint8
 uint16
 uint32
 uint64
 Boolean
 fixed point
Parameters
Analyzer Tab
ViewsSpectrum — Type of spectrum to display
Power
(default)  Power Density
 RMS
Set the type of spectrum to display as one of these values:
Power
— Spectrum Analyzer shows the power spectrum.Power Density
— Spectrum Analyzer shows the power spectral density. The power spectral density is the squared magnitude of the spectrum normalized to a bandwidth of 1 Hz.RMS
— Spectrum Analyzer shows the root mean squared spectrum. Use this option to view the frequency of voltage or current signals.
Tunable: Yes
Dependency
To enable this parameter, set the Input
Domain parameter on the
Estimation tab to
Time
.
Programmatic Use
Block Parameter:
SpectrumType 
Type: character vector or string scalar 
Spectrogram — Type of spectrogram to display
Power
(default)  Power Density
 RMS
Set the type of spectrogram to display as one of these values:
Power
— Spectrum Analyzer shows the power spectrogram.Power Density
— Spectrum Analyzer shows the power density of the spectrogram. The power spectrogram density is the squared magnitude of the spectrogram normalized to a bandwidth of 1 Hz.RMS
— Spectrum Analyzer shows the root mean square of the spectrogram. The rootmeansquare shows the square root of the mean square. Use this option to view the frequency of voltage or current signals.
Tunable: Yes
Dependency
To enable this parameter, set the Input
Domain parameter on the
Estimation tab to
Time
.
Programmatic Use
Block Parameter:
SpectrumType 
Type: character vector or string scalar 
Sample Rate (Hz) — Sample rate the scope uses in Hz
Inherited
(default)  positive scalar
Specify the sample rate the scope uses in Hz as one of the following:
Inherited
–– Use this option to specify the same sample rate as the input signal.Positive scalar –– The sample rate you specify must be at least twice the sample rate of the input signal. Otherwise, you might see unexpected behavior when visualizing your signal in the scope due to aliasing.
When the signal frame size changes, the sample rate the scopes uses changes accordingly which in turn updates the frequency span of the spectrum display. For an example that shows this behavior, see Display VariableSize Input Signals on Spectrum Analyzer.
To display the sample rate on the status bar, rightclick the status bar at the bottom
of the Spectrum Analyzer window and select Sample
Rate
.
Tunable: Yes
Programmatic Use
Block Parameter:
SampleRate , SampleRateSource 
Type:
double 
RBW (Hz) — Resolution bandwidth in Hz
Auto
(default)  Input port
 positive scalar
Specify the resolution bandwidth in Hz. This parameter defines the smallest positive frequency
that can be resolved by the scope. By default, this parameter is set to
Auto
. In this case, the Spectrum Analyzer determines the
appropriate value to ensure that there are 1024 RBW intervals over the specified
frequency span.
If you set this parameter to Input port
, you can specify
the RBW value through an input port on the block.
If you set this parameter to a numeric value, the value must allow at least two RBW intervals over the specified frequency span. In other words, the ratio of the overall frequency span to RBW must be greater than two:
$$\frac{span}{RBW}>2$$
To display this property on the status bar, rightclick the status bar at the bottom of the
Spectrum Analyzer window and select RBW
.
Tunable: Yes
Programmatic Use
Block Parameter: RBWSource , RBW 
Type: character vector, string scalar, double 
Offset (Hz) — Offset to apply to frequency axis
0
(default)  scalar  vector
Specify the offset to apply to the frequency axis (xaxis) in units of Hz as one of the following:
Scalar — Apply the same frequency offset to all channels.
Vector — Apply a specific frequency offset for each channel. The vector length must be equal to the number of input channels.
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 Span (Hz) parameter.
Tunable: Yes
Programmatic Use
Block
Parameter:
FrequencyOffset 
Type:
double 
Num Inputs — Number of input ports
1 (default)  integer between 1 and 96
The number of input ports to the block, specified as an integer between 1 and 96. To change the number of input ports, drag a new input signal line to the block and the block automatically creates new ports.
Programmatic Use
Block Parameter:
NumInputPorts 
Type: character vector or string scalar 
Values: scalar between 1 and 96 
Open at Simulation Start — Automatically open scope when simulation starts
on (default)  off
Select this parameter to automatically open the Spectrum Analyzer window when you run the simulation.
Programmatic Use
Block Parameter:
OpenAtSimulationStart 
Type: logical 
Font Size — Font size of labels
Small
(default)  Medium
 Large
 Extra Large
Specify the font size of labels in the display as Small
,
Medium
, Large
, and
Extra Large
.
Tunable: Yes
Programmatic Use
Block Parameter:  
Type: character vector or string scalar 
Plot Type — Plot type
Line
(default)  Stem
Specify whether to display a Line
or
Stem
plot in the Spectrum display.
Tunable: Yes
Dependency
To enable this parameter:
Select Spectrum in the Analyzer tab.
Select the Normal Trace check box in the Spectrum tab.
Programmatic Use
Block Parameter:
PlotType 
Type: character vector or string scalar 
YLabel — yaxis label
character vector  string scalar
Specify the yaxis label in the Spectrum display as
a character vector or a string scalar. To display signal units, add
(%<SignalUnits>)
to the label. When
simulation starts, Simulink replaces (%SignalUnits)
with the units
associated with the signals.
For example, for a velocity signal with units of m/s enter
Velocity (%<SignalUnits>)
Tunable: Yes
Dependency
To enable this parameter, select Spectrum in the Analyzer tab.
Programmatic Use
Block Parameter:
YLabel 
Type: character vector or string scalar 
YLimits — yaxis limits
[−80
20
]  [ymin ymax
]
Specify the yaxis limits in the Spectrum Analyzer
display as a twoelement numeric vector of the form [ymin
ymax
]. The units of the yaxis limits
depend on the Spectrum Unit in the
Spectrum tab.
Tunable: Yes
Dependency
To enable this parameter, select Spectrum in the Analyzer tab.
Programmatic Use
Block Parameter:
YLimits 
Type:
double 
Title — Display title
character vector  string
Specify the display title. Enter %<SignalLabel>
to use the signal labels in the Simulink model as the axes titles.
Tunable: Yes
Programmatic Use
Block
Parameter:
Title 
Type: character vector or string 
Show Grid — Show internal grid lines
on
(default)  off
Select this check box to show the grid in the Spectrum Analyzer display.
Tunable: Yes
Programmatic Use
Block
Parameter:
ShowGrid 
Type:
logical 
Color Map — Spectrogram colormap
jet
(default)  hot
 bone
 cool
 copper
 gray
 parula
 threecolumn matrix
Select a valid colormap name for the spectrogram, or enter a
threecolumn matrix with values in the range [0,1] defining RGB
triplets. For more information about colormaps, see colormap
.
Tunable: Yes
Dependency
To enable this parameter, select Spectrogram in the Analyzer tab.
Programmatic Use
Block Parameter:
Colormap 
Type: character vector or string scalar 
Color Limits — Color limits of spectrogram
[80, 20
] (default)  [colorMin colorMax
]
Specify the color limits of the spectrogram as a twoelement numeric
vector of the form [colorMin colorMax
]. The units of
the color limits directly depend upon the Spectrum
Unit in the Spectrogram tab.
Tunable: Yes
Dependencies
To enable this parameter, select Spectrogram in the Analyzer tab.
Programmatic Use
Block Parameter:
ColorLimits 
Type:
double 
Preserve colors for copy to clipboard — Preserve colors when copying to clipboard
off
(default)  on
When you select this parameter, the scope preserves the colors when you copy the display to the clipboard using the Copy Display and the Print options in the Analyzer tab > Share section.
Tunable: Yes
Background — Window background
black (default)  color picker
Specify the background color in the scope figure.
Tunable: Yes
Axes — Axes background color
black (default)  color picker
Specify the background color of the axes.
Tunable: Yes
Labels — Color of labels
gray (default)  color picker
Specify the color of the labels, grid, and the channel names in the legend.
Tunable: Yes
Line — Channel for line property settings
channel names
Specify the channel for which you want to modify the visibility, line color, style, width, and marker properties.
Tunable: Yes
Visible — Channel visibility
on
(default)  off
Select this check box to display the channel you have selected. If you clear this check box, the selected channel is no longer visible. You can also click the signal name in the legend to control its visibility. For more details, see Legend.
Tunable: Yes
Style — Line style

(default)  :
 
.  
 None
Specify the line style for the selected channel.
Tunable: Yes
Width — Line width
1.5
(default)  0.5
 1
 2
 ...
Specify the line width for the selected channel.
Tunable: Yes
Marker — Data point markers
None
(default)  +
 x
 ...
Specify a data point marker for the selected channel. This parameter is similar to the Marker property for plots. You can choose any of the marker symbols from the dropdown list.
Tunable: Yes
Color — Line color
yellow (default)  color picker
Specify the line color for the selected channel.
Tunable: Yes
Legend — Show or hide signal legend
button
Click the Legend button to enable the Spectrum Analyzer to display the signal legend. The legend displays the signal names from the model. For signals with multiple channels, the scope appends a channel index after the signal name. Continuous signals have straight lines before their names and discrete signals have stepshaped lines.
You can control which signals are visible using the legend. To hide a signal, in the scope legend, click the signal name. To display the signal, click the signal name again. Alternatively, you can control which signal is visible using the Visible parameter in the Spectrum Analyzer Settings ().
To display only one signal and hide all other signals, rightclick the name of the signal you want the scope to display. To show all signals, press Esc.
Note
The legend displays only the first 20 signals. You cannot view or control any additional signals from the legend.
Tunable: Yes
Dependency
To enable the Legend, select Spectrum in the Analyzer tab.
Programmatic Use
Block Parameter:
ShowLegend 
Type:
logical 
Colorbar — Show or hide color bar
button
When you select the Colorbar button, the Spectrum Analyzer shows the color bar.
Tunable: Yes
Dependencies
To enable the Colorbar button, select Spectrogram in the Analyzer tab.
Programmatic Use
Block Parameter:
ShowColorbar 
Type:
logical 
Layout — Stack axes vertically or horizontally
vertical layout (default)  horizontal layout
Stack axes vertically or horizontally by selecting the appropriate configuration in the layout grid.
Tunable: Yes
Dependencies
To enable the Layout, select Spectrum and Spectrogram in the Analyzer tab.
Programmatic Use
Block Parameter:
AxesLayout 
Type: character vector or string scalar 
Copy Display — Send display to clipboard
button
Click this button to copy the scope display to the clipboard. You can preserve the color in the display by selecting the Preserve colors for copy to clipboard parameter.
Print — Print display
button
Click this button to save the scope display as an image or a PDF or to print the display.
Estimation Tab
DomainInput Domain — Domain of the input signal
Time
(default)  Frequency
The domain of the input signal you want to visualize. If you visualize timedomain signals, the scope transforms the signal to the frequency spectrum based on the algorithm you specify in the Method parameter.
Programmatic Use
Block Parameter:
InputDomain 
Type: character vector or string scalar 
Frequency (Hz) — Frequency vector
Auto
(default)  Input port
 monotonically increasing vector
Set the frequency vector which determines the xaxis of the display to one of these values:
Auto
— The scope calculates the frequency vector from the length of the input. For more details, see Frequency Vector.Input port
— You specify the frequency vector at the Frequency input port on the block.Custom vector — You specify a custom vector as the frequency vector. The length of the custom vector must be equal to the frame size of the input signal.
Tunable: Yes
Dependency
To enable this parameter, set Input Domain to
Frequency
.
Programmatic Use
Block Parameter:
FrequencyVectorSource ,
FrequencyVector 
Type: character vector,
string scalar,
double 
Input Unit — Units of frequency input
dBm
(default)  dBuV
(since R2023b)  dBV
 dBW
 Vrms
 Watts
 None
Select the units of the frequencydomain input. This parameter enables the Spectrum Analyzer to scale frequency data when you select a different display unit in the Spectrum Unit parameter in the Estimation tab.
Tunable: Yes
Dependency
To enable this parameter, set Input Domain to
Frequency
.
Programmatic Use
Block Parameter:
InputUnits 
Type: character vector or string scalar 
Method — Spectrum estimation method
Filter Bank
(default)  Welch
Select the spectrum estimation method as one of the following:
Filter Bank
–– Use an analysis filter bank to estimate the power spectrum. Compared to Welch's method, this method has a lower noise floor, better frequency resolution, lower spectral leakage, and requires fewer samples per update.Welch
–– Use Welch's method of averaged modified periodograms.
For more details on these methods, see Algorithms.
Tunable: Yes
Dependency
To use this parameter, set Input Domain to
Time
.
Programmatic Use
Block Parameter:
Method 
Type: character vector or string scalar 
Sharpness — Sharpness of lowpass filter
0.5
(default)  nonnegative scalar in the range [0,1]
Specify the sharpness of the prototype lowpass filter as a real nonnegative scalar in the range [0,1].
Increasing the filter sharpness decreases the spectral leakage and gives a more accurate power reading.
Tunable: Yes
Dependencies
To enable this property, set Method to
Filter bank
.
Programmatic Use
Block Parameter:
FilterSharpness 
Type:
double 
Averaging Method — Smoothing method
VBW
(default)  Exponential
Specify the smoothing method as one of the following:
VBW
— Video bandwidth method. The block uses a lowpass filter to smooth the trace and decrease the noise. Use the VBW (Hz) parameter to specify the video bandwidth (VBW) value.Exponential
— Weighted average of samples. The block computes the average over samples weighted by an exponentially decaying forgetting factor. Use the Forgetting Factor parameter to specify the weighted forgetting factor.
For more information on the averaging methods, see Averaging Method.
Tunable: Yes
Dependency
To enable this parameter, set Input Domain to
Time
.
Programmatic Use
Block Parameter:
AveragingMethod 
Type: character vector or string scalar 
VBW (Hz) — Video bandwidth
Auto
(default)  Input port
 positive scalar
Specify the video bandwidth as one of the following: S
Auto
–– The Spectrum Analyzer adjusts the VBW such that the equivalent forgetting factor is 0.9.Input port
–– You specify the frequency vector at the VBW input port on the block.Positive scalar –– You specify a positive scalar. The Spectrum Analyzer adjusts the VBW using this value. The value you specify must be less than or equal to Sample Rate (Hz)/2.
For more details on the video bandwidth method, see Averaging Method.
The Spectrum Analyzer shows the VBW value in the status bar at the
bottom of the display. To display the VBW value, rightclick the status
bar and select VBW
.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Averaging Method
toVBW
.
Programmatic Use
Block Parameter:
VBWSource ,
VBW 
Type:
double 
Forgetting Factor — Forgetting factor of weighted average method
0.9
(default)  scalar in the range [0,1]
Specify the forgetting factor of the exponential weighted averaging method as a scalar in the range [0,1].
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Averaging Method to
Exponential
.
Programmatic Use
Block Parameter:
ForgettingFactor 
Type:
double 
Frequency Span — Frequency span mode
Full
(default)  Span and Center Frequency
 Start and Stop Frequencies
Specify the frequency span mode as one of the following:
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 (Hz) and Center Frequency (Hz) parameters.Start and Stop Frequencies
–– The Spectrum Analyzer computes and plots the spectrum over the interval specified by the Start Frequency (Hz) and Stop Frequency (Hz) parameters.
Tunable: Yes
Dependency
To enable this parameter, set Input Domain to
Time
.
Programmatic Use
Block Parameter:
FrequencySpan 
Type: character vector or string scalar 
Span (Hz) — Frequency span to compute spectrum in Hz
10e3
(default)  real positive scalar
Specify the frequency span in Hz over which the Spectrum Analyzer computes and plots the spectrum. The overall span, defined by this parameter and the Center Frequency (Hz) parameter, must fall within the Nyquist Frequency Interval. This parameter defines the range of the values shown on the Frequency axis in the Spectrum Analyzer window.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Frequency Span to
Span and Center Frequency
.
Programmatic Use
Block Parameter:
Span 
Type:
double 
Center Frequency (Hz) — Center of frequency span in Hz
0
(default)  real scalar
Specify the center of the frequency span in Hz over which the Spectrum Analyzer computes and plots the spectrum. Use this parameter with the Span (Hz) parameter to define the frequency span around a center frequency. This parameter defines the midpoint of the Frequency axis in the Spectrum Analyzer window.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Frequency Span to
Span and Center Frequency
.
Programmatic Use
Block Parameter:
CenterFrequency 
Type:
double 
Start Frequency (Hz) — Start frequency in Hz
5e3
(default)  scalar
Specify the starting frequency in Hz of the frequency interval over which the Spectrum Analyzer computes and plots the spectrum. The overall span, which is defined by this parameter and the Stop Frequency (Hz) parameter, must fall within the Nyquist Frequency Interval. This parameter defines the leftmost value on the Frequency axis in the Spectrum Analyzer window.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Frequency Span to
Start and Stop Frequencies
.
Programmatic Use
Block Parameter:
StartFrequency 
Type:
double 
Stop Frequency (Hz) — Stop frequency in Hz
5e3
(default)  scalar
Specify the stop frequency in Hz of the frequency interval over which the Spectrum Analyzer computes and plots the spectrum. The overall span, which is defined by this parameter and the Start Frequency (Hz) parameter, must fall within the Nyquist Frequency Interval. This parameter defines the rightmost value on the Frequency axis in the Spectrum Analyzer window.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Frequency Span to
Start and Stop Frequencies
.
Programmatic Use
Block Parameter:
StopFrequency 
Type:
double 
Window — Windowing method
Hann
(default)  BlackmanHarris
 Chebyshev
 Flat Top
 Hamming
 Kaiser
 Rectangular
 custom window function name
Specify the windowing method to apply to the spectrum. Windowing is used to control the effect of sidelobes in spectral estimation. The window you specify affects the window length required to achieve a resolution bandwidth and the required number of samples per update. For more information about windowing, see Windows.
You can use your own spectral estimation window by directly specifying a custom window function name in the Window parameter.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Method to
Welch
.
Programmatic Use
Block Parameter:
Window ,
CustomWindow 
Type: character vector or string scalar 
Attenuation (dB) — Sidelobe attenuation in dB
60
(default)  scalar greater than or equal to 45
Specify the sidelobe attenuation in dB as a scalar greater than or
equal to 45
.
Tunable: Yes
Dependency
To enable this parameter, set Window to
Chebyshev
or
Kaiser
.
Programmatic Use
Block Parameter:
SidelobeAttenuation 
Type:
double 
Overlap (%) — Percentage of overlap
0
(default)  scalar in the range [0 100)
Specify the percentage of overlap between the previous and the current buffered data segments as a scalar in the range [0 100). The overlap creates a window segment that the scope uses to compute a spectral estimate. The value must be greater than or equal to zero and less than 100.
Tunable: Yes
Dependency
To enable this parameter, set:
Input Domain to
Time
.Method to
Welch
.
Programmatic Use
Block Parameter:
OverlapPercent 
Type:
double 
Measurements Tab
ChannelChannel — Channel for which to obtain measurements
1
(default)  positive integer
The channel for which you need to obtain measurements, specified as a positive integer in the range [1 N], where N is the number of input channels.
Tunable: Yes
Dependency
To enable this parameter, pass some data through the scope.
Programmatic Use
See MeasurementChannel
.
Data Cursors — Enable cursor measurements
button
Click the Data Cursors button to enable data cursor measurements. Each cursor tracks a vertical line along the signal. The scope displays the difference between x and yvalues of the signal at the two cursors in the box between the cursors.
Tunable: Yes
Programmatic Use
See Enabled
.
Snap to data — Snap cursors to data
off
(default)  on
Select this parameter to position the cursors on the signal data points.
Tunable: Yes
Programmatic Use
See SnapToData
.
Lock cursor spacing — Lock cursor spacing
off
(default)  on
Select this parameter to lock the frequency difference between the two cursors.
Tunable: Yes
Programmatic Use
See LockSpacing
.
Peak Finder — Enable peak finder measurements
button
Click the Peak Finder button to enable peak finder measurements. An arrow appears on the plot at each maxima and a Peaks panel appears at the bottom of the scope window.
Tunable: Yes
Programmatic Use
See Enabled
.
Num Peaks — Maximum number of peaks to show
3
(default)  positive integer less than 100
Specify the maximum number of peaks to show as a positive integer less than 100.
Tunable: Yes
Programmatic Use
See NumPeaks
.
Min Height — Level above which scope detects peaks
Inf
(default)  real scalar value
Specify the level above which the scope detects peaks as a real scalar.
Tunable: Yes
Programmatic Use
See MinHeight
.
Min Distance — Minimum number of samples between adjacent peaks
1
(default)  positive integer
Specify the minimum number of samples between adjacent peaks as a positive integer.
Tunable: Yes
Programmatic Use
See MinDistance
.
Threshold — Minimum difference between height of peak and its neighboring samples
0
(default)  nonnegative scalar
Specify the minimum difference between the height of the peak and its neighboring samples as a nonnegative scalar.
Tunable: Yes
Programmatic Use
See Threshold
.
Label Peaks — Label peaks
button
Click the Label Peaks button to label the peaks. The scope displays the labels (P1, P2, …) above the arrows in the plot.
Tunable: Yes
Programmatic Use
See LabelPeaks
.
Distortion — Enable distortion measurements
button
Click the Distortion button to enable distortion measurements. A Distortion panel appears at the bottom of the scope window when you click this button.
Tunable: Yes
Programmatic Use
See Enabled
.
Distortion Type — Type of measurement to display
Harmonic
(default)  Intermodulation
Specify the type of measurement data to display as Harmonic
or Intermodulation
. For more details, see Distortion Measurements.
Tunable: Yes
Programmatic Use
See Type
.
Num Harmonics — Number of harmonics to measure
6
(default)  positive integer
Specify the number of harmonics to measure as a positive integer less than or equal to 99.
Tunable: Yes
Dependency
To enable this parameter, set Distortion Type to Harmonic
.
Programmatic Use
See NumHarmonics
.
Label Harmonics — Label harmonics
off
(default)  on
When you select this parameter, the Spectrum Analyzer adds numerical labels to harmonics in the spectrum display.
Tunable: Yes
Programmatic Use
See LabelValues
.
Label Frequencies — Label frequencies
off
(default)  on
When you select this parameter, the Spectrum Analyzer adds numerical labels to the firstorder intermodulation product and thirdorder frequencies in the Spectrum Analyzer display.
Tunable: Yes
Programmatic Use
See LabelValues
.
Spectrum Tab
Note
This tab appears when you select Spectrum in the Analyzer tab.
TwoSided Spectrum — Enable twosided spectrum view
on
(default)  off
Select this check box to enable a twosided spectrum view. In this view, the Spectrum Analyzer shows both negative and positive frequencies. When the input signal is complexvalued, you must select this parameter. If you clear this check box, the Spectrum Analyzer shows a onesided spectrum with positive frequencies only. In this case, the input signal data must be real valued.
When you clear this check box, the Spectrum Analyzer uses power folding.
The yaxis values are twice the amplitude that they
would be if you were to select this parameter, except at
0
and the Nyquist frequency. A onesided
power spectral density (PSD) contains the total power of the signal in
the frequency interval from DC to half the Nyquist rate. For more
information, see pwelch
.
Tunable: Yes
Programmatic Use
Block
Parameter:
PlotAsTwoSidedSpectrum 
Type:
logical 
Normal Trace — Normal trace view
on
(default)  off
When you select this check box, the Spectrum Analyzer calculates and plots the power spectral estimates. The Spectrum Analyzer performs a smoothing operation by averaging several spectral estimates and continues its spectral computations even when you clear this parameter.
Tunable: Yes
Dependencies
To clear this check box, first select either the MaxHold Trace or the MinHold Trace parameters.
To enable this parameter, select Spectrum in the Analyzer tab.
Programmatic Use
Block Parameter:
PlotNormalTrace 
Type:
logical 
MaxHold Trace — Maximum hold trace view
off
(default)  on
Select this check box to enable the Spectrum Analyzer to plot the maximum spectral values of all the estimates. The Spectrum Analyzer computes the maximumhold spectrum at each frequency bin by keeping the maximum value of all the power spectrum estimates. When you clear this check box, the Spectrum Analyzer resets its maximumhold computations.
Tunable: Yes
Dependency
To enable this parameter, select Spectrum in the Analyzer tab.
Programmatic Use
Block Parameter:
PlotMaxHoldTrace 
Type:
logical 
MinHold Trace — Minimum hold trace view
off
(default)  on
Select this check box to enable the Spectrum Analyzer to plot the minimum spectral values of all the estimates. The Spectrum Analyzer computes the minimumhold spectrum at each frequency bin by keeping the minimum value of all the power spectrum estimates. When you clear this check box, the Spectrum Analyzer resets its minimumhold computations.
Tunable: Yes
Dependency
To enable this parameter, select Spectrum in the Analyzer tab.
Programmatic Use
Block Parameter:
PlotMinHoldTrace 
Type:
logical 
Frequency Scale — Scale of frequency axis
Linear
(default)  Log
Specify the scale to display frequencies as
Linear
or Log
.
When the frequency span contains negative frequency values, you cannot
choose the logarithmic option.
Tunable: Yes
Dependency
To set the Frequency Scale to
Log
, clear the TwoSided
Spectrum check box in the Trace
Options section in the Spectrum
or the Spectrogram tab (if enabled). If you
select the TwoSided Spectrum check box, then
the Frequency Scale parameter is set to
Linear
.
Programmatic Use
Block Parameter:
FrequencyScale 
Type: character vector or string scalar 
Reference load (Ω) — Reference load in Ω
1
(default)  positive real scalar
Specify the reference load in ohms that the Spectrum Analyzer uses as a reference to compute the power values.
Tunable: Yes
Dependency
To enable this parameter, set:
Spectrum type to
Power
orPower Density
.Spectrum Unit to any option other than
dBFS
ordBFS/Hz
.
Programmatic Use
Block
Parameter:
ReferenceLoad 
Type:
double 
Spectrum Unit — Units of the spectrum
dBm
(default)  dBFS
 dBV
 dBuV
(since R2023b)  dBW
 Vrms
 Watts
 dBm/Hz
 dBW/Hz
 dBFS/Hz
 Watts/Hz
 Auto
Specify the units in which the Spectrum Analyzer displays the power values as one of the following:
dBm
dBFS
dBuV
(since R2023b)dBV
dBW
Vrms
Watts
dBm/Hz
dBW/Hz
dBFS/Hz
Watts/Hz
Auto
Tunable: Yes
Dependency
The units available depend on the value you choose for the Spectrum parameter in the Analyzer tab.
Estimation tab > Input Domain parameter  Analyzer tab > Spectrum option  Available Units 

Time  Power  dBm ,
dBW ,
dBFS ,
Watts 
Power
Density  dBm/Hz ,
dBW/Hz ,dBFS/Hz ,
Watts/Hz  
RMS  dBuV (since R2023b),
dBV ,
Vrms  
Frequency  ―  Auto ,
dBm , dBuV (since R2023b),
dBV ,
dBW ,
Vrms ,
Watts 
If you set the Input Domain parameter to
Frequency
and the Spectrum
Unit parameter to Auto
,
the Spectrum Analyzer assumes the spectrum units to be equal to
input units specified in the Estimation tab >
Input Unit parameter. If you set the
Input Domain parameter to
Time
and the Spectrum
Unit parameter to any option other than
Auto
, the Spectrum Analyzer converts
the units specified in the Input Unit parameter
to the units specified in the Spectrum Unit
parameter.
Programmatic Use
Block Parameter:
SpectrumUnits 
Type: character vector or string scalar 
Full Scale — Full scale for dBFS units
Auto
(default)  positive real scalar
The full scale used for the decibel full scale (dBFS) units. By default, the Spectrum Analyzer uses the entire spectrum scale. Specify a positive real scalar for the dBFS full scale.
Tunable: Yes
Dependencies
To enable this parameter:
In the Analyzer tab, set the spectrum type to
Power
orPower Density
.In the Estimation tab, set Input Domain to
Time
.In the Spectrum tab, set Spectrum Unit to
dBFS
ordBFS/Hz
(when spectrum type is set toPower Density
).
Programmatic Use
Block Parameter:
FullScale 
Type:
double 
Spectrogram Tab
Note
This tab appears when you select Spectrogram in the Analyzer tab.
Channel — Channel for which spectrogram is plotted
1
(default)  character vector of a positive integer  string scalar of a positive integer
Select the signal channel for which the spectrogram settings apply.
Tunable: Yes
Dependency
To enable this parameter, select Spectrogram in the Analyzer tab.
Programmatic Use
Block Parameter:
SpectrogramChannel 
Type: character vector,
string scalar, double 
Time Resolution (s) — Time resolution in seconds
Auto
(default)  positive scalar
Time resolution is the amount of data, in seconds, used to compute a spectrogram line. The minimum attainable resolution is the amount of time it takes to compute a single spectral estimate. The tooltip displays the minimum attainable resolution given the current Spectrum Analyzer settings.
When you set RBW (Hz) and Time
Resolution (s) to Auto
, then
the Spectrum Analyzer adjusts the RBW value such that there are 1024 RBW
intervals in one frequency span and sets the time resolution is set to
1/RBW
.
When you set RBW (Hz) to
Auto
and Time Resolution
(s) to a positive scalar, then time resolution becomes
the main control and RBW is set to 1/Time Resolution
(s) Hz.
When you set RBW (Hz) to a positive scalar and
Time Resolution (s) to
Auto
, then RBW becomes the main control
and the time resolution is set 1/RBW (Hz) s.
When you set RBW (Hz) and Time Resolution (s) to a positive value, then time resolution must be equal to or larger than the minimum attainable time resolution defined by 1/RBW (Hz). 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 (Hz).
Tunable: Yes
Dependency
To enable this parameter, select Spectrogram
in the Analyzer tab and set Input
Domain to Time
in the
Estimation tab.
Programmatic Use
Block Parameter:
TimeResolutionSource ,
TimeResolution 
Type: character vector,
string scalar, double 
Time Span (s) — Time span in seconds
Auto
(default)  positive scalar
The time span over which the Spectrum Analyzer displays the
spectrogram specified as a positive scalar in seconds. The time span is
the product of the desired number of spectral lines and the time
resolution. When you set this parameter to
Auto
, the spectrogram displays 100
spectrogram lines at any given time. Otherwise, the spectrogram uses the
time duration you specify in this parameter. The time span that you
specify must be at least two times larger than the duration of the
number of samples required for a spectral update.
Tunable: Yes
Dependency
To enable this parameter, select Spectrogram
in the Analyzer tab and set Input
Domain to Time
in the
Estimation tab.
Programmatic Use
Block Parameter:
TimeSpanSource ,
TimeSpan 
Type: character vector,
string scalar, double 
TwoSided Spectrum — Enable twosided spectrum view
on
(default)  off
Select this check box to enable a twosided spectrum view. In this view, the Spectrum Analyzer shows both negative and positive frequencies. When the input signal is complexvalued, you must select this parameter. If you clear this check box, the Spectrum Analyzer shows a onesided spectrum with positive frequencies only. In this case, the input signal data must be real valued.
When you clear this check box, the Spectrum Analyzer uses power folding.
The yaxis values are twice the amplitude that they
would be if you were to select this parameter, except at
0
and the Nyquist frequency. A onesided
power spectral density (PSD) contains the total power of the signal in
the frequency interval from DC to half the Nyquist rate. For more
information, see pwelch
.
Tunable: Yes
Programmatic Use
Block
Parameter:
PlotAsTwoSidedSpectrum 
Type:
logical 
Spectral Mask Tab
Note
This tab appears when you select Spectrum in the
Analyzer tab and set the Spectrum
type to be Power
or Power
Density
.
Upper Mask — Enable upper spectral mask
button
Select Upper Mask to display the upper mask in the spectrum plot. The Spectral Mask panel appears at the bottom of the Spectrum Analyzer window and displays mask details, such as number of times a mask succeeded, number of times a mask failed, channels causing the mask failure, and so on.
Use the Upper Limits parameter to specify the upper mask. If the entire spectrum plot is below the upper mask, the upper mask looks green. In all other cases, the upper mask looks red.
Tunable: Yes
Programmatic Use
See EnabledMasks
.
Lower Mask — Enable lower spectral mask
button
Select Lower Mask to display the lower mask in the spectrum plot. The Spectral Mask panel appears at the bottom of the Spectrum Analyzer window and displays mask details, such as number of times a mask succeeded, number of times a mask failed, channels causing the mask failure, and so on.
Use the Lower Limits parameter to specify the lower mask. If the entire spectrum plot is above the lower mask, the lower mask looks green. In all other cases, the lower mask looks red.
Tunable: Yes
Programmatic Use
See EnabledMasks
.
Upper Limits — Limit for upper spectral mask
Inf
(default)  scalar  twocolumn matrix
Specify the limit for the upper spectral mask as a scalar or a twocolumn matrix.
If UpperMask
is a scalar, the upper limit mask
uses the same power value for all frequencies specified in the Spectrum
Analyzer.
If you specify a matrix, the first column contains the frequency values (Hz), which correspond to the xaxis values. The second column contains the power values, which correspond to the associated yaxis values.
To apply offsets to the power and frequency values, use the Reference Level (dBr) and the Frequency Offset (Hz) parameters.
Tunable: Yes
Programmatic Use
See UpperMask
.
Lower Limits — Limit for lower spectral mask
Inf
(default)  scalar  twocolumn matrix
Specify the limit for the lower spectral mask as a scalar or a twocolumn matrix.
If LowerMask
is a scalar, the lower limit mask
uses the same power value for all frequencies specified in the Spectrum
Analyzer.
If you specify a matrix, the first column contains the frequency values (Hz), which correspond to the xaxis values. The second column contains the power values, which correspond to the associated yaxis values.
To apply offsets to the power and frequency values, use the Reference Level (dBr) and the Frequency Offset (Hz) parameters.
Tunable: Yes
Programmatic Use
See LowerMask
.
Reference Level (dBr) — Reference level for mask power values
0
(default)  real scalar  Spectrum peak
Specify the reference level for mask power values as a numeric scalar
or set it to Spectrum peak
.
When you set Reference Level (dBr) to a scalar value, the Spectrum Analyzer uses this value as the reference to the power values (in dBr) for the upper mask and the lower mask of the Spectrum Analyzer. The reference level should have the same units as the Spectrum Unit parameter in the Spectrum tab.
When you set Reference Level (dBr) to
Spectrum peak
, the Spectrum Analyzer uses
the peak value of the current spectrum of the
Channel in the Spectral
Mask tab as the reference power value.
Tunable: Yes
Programmatic Use
See ReferenceLevel
and CustomReferenceLevel
.
Channel — Input channel with peak spectrum
1
(default)  integer
Select the input channel which the Spectrum Analyzer uses to determine
the mask reference level. The peak value of the spectrum in this channel
becomes the mask reference level when you set the Reference
Level (dBr) parameter to Spectrum
peak
.
Tunable: Yes
Dependency
To enable this parameter, set Reference Level
(dBr) to Spectrum peak
and
display some data on the scope.
Programmatic Use
See SelectedChannel
.
Frequency Offset (Hz) — Frequency offset in Hz
0
(default)  finite numeric scalar
Specify the frequency offset in Hz as a finite numeric scalar. Using this value, the Spectrum Analyzer offsets the frequency values in the Upper Mask and the Lower Mask parameters.
Tunable: Yes
Programmatic Use
See MaskFrequencyOffset
.
Channel Measurements Tab
Note
This tab appears when you select Spectrum in the Analyzer tab.
Channel — Channel for computing occupied bandwidth and adjacent channel power ratio
1
(default)  positive integer
Specify the channel over which the Spectrum Analyzer computes and displays the occupied bandwidth and adjacent channel power ratio as a positive integer in the range [1 N], where N is the number of input channels.
Tunable: Yes
Dependency
To enable this parameter, pass data through the scope.
Programmatic Use
See MeasurementChannel
.
Channel Measurements — Enable channel measurements
button
Click Channel Measurements to enable channel measurements.
Tunable: Yes
Programmatic Use
See Enabled
.
Type — Type of measurement data to display
Occupied BW
(default)  ACPR
Specify the type of measurement data to display as
Occupied BW
or
ACPR
.
Tunable: Yes
Programmatic Use
See Type
.
Occupied BW (%) — Percentage of power to compute occupied bandwidth
99
(default)  positive scalar
Specify the percentage of power over which the Spectrum Analyzer computes the occupied bandwidth as a positive scalar.
Tunable: Yes
Dependency
To enable this parameter, set Type to
Occupied BW
.
Programmatic Use
See PercentOccupiedBW
.
Frequency Span — Frequency span mode
Span and Center
Frequency
(default)  Start and Stop Frequencies
Specify the frequency span mode as one of the following:
Span and Center Frequency
–– Measure over a frequency range specified in Span (Hz) and around the frequency value specified in Center Frequency (Hz).Start and Stop Frequencies
–– Measure over the frequency range [Start Frequency (Hz), Stop Frequency (Hz)].
Tunable: Yes
Programmatic Use
See FrequencySpan
.
Span (Hz) — Frequency span in Hz
2000
(default)  positive scalar
Specify the frequency span over which the Spectrum Analyzer computes the channel measurements as a positive scalar in Hz.
Tunable: Yes
Dependency
To enable this parameter, set Frequency Span
to Span and Center Frequency
.
Programmatic Use
See Span
.
Center Frequency (Hz) — Center frequency of span in Hz
0
(default)  real scalar
Center frequency of the span over which the object computes the channel measurements, specified as a real scalar in Hz.
Tunable: Yes
Dependency
To enable this parameter, set Frequency Span
to Span and Center Frequency
.
Programmatic Use
See CenterFrequency
.
Start Frequency (Hz) — Start frequency in Hz
1000
(default)  real scalar
Specify the start frequency in Hz over which the Spectrum Analyzer computes the channel measurements.
Tunable: Yes
Dependency
To enable this parameter, set Frequency Span
to Start and Stop Frequencies
.
Programmatic Use
See StartFrequency
.
Stop Frequency (Hz) — Stop frequency in Hz
1000
(default)  real scalar
Specify the stop frequency in Hz over which the Spectrum Analyzer computes the channel measurements.
Tunable: Yes
Dependency
To enable this parameter, set Frequency Span
to Start and Stop Frequencies
.
Programmatic Use
See StopFrequency
.
Num Pairs — Number of adjacent channel pairs
2
(default)  positive integer in range [1
,
12
]
Specify the number of adjacent channel pairs as a positive integer in
the range [1
, 12
].
Tunable: Yes
Dependency
To enable this parameter, set Type to
ACPR
.
Programmatic Use
See NumOffsets
.
Offsets (Hz) — ACPR offsets in Hz
[2000 3500]
(default)  vector
Specify the frequency of the adjacent channel relative to the center frequency of the main channel as a real vector of length equal to the number of offset pairs specified in Num Pairs.
Tunable: Yes
Dependency
To enable this parameter, set Type to
ACPR
.
Programmatic Use
See ACPROffsets
.
Adjacent BW (Hz) — Adjacent channel bandwidth in Hz
1000
(default)  positive scalar
Specify the adjacent channel bandwidth in Hz as a positive scalar.
Tunable: Yes
Dependency
To enable this parameter, set Type to
ACPR
.
Programmatic Use
See AdjacentBW
.
Filter Shape — Filter shape
None
(default)  RRC
 Gaussian
Specify the filter shape for the main and adjacent channels as
None
, RRC
, or
Gaussian
.
Tunable: Yes
Dependency
To enable this parameter, set Type to
ACPR
.
Programmatic Use
See FilterShape
.
Rolloff Factor — Rolloff factor
0.5
(default)  real scalar in range [0
,
1
]
Specify the rolloff factor as a real scalar in the range
[0
, 1
].
Tunable: Yes
Dependency
To enable this parameter, set Type to
ACPR
and Filter
Shape to RRC
.
Programmatic Use
See FilterCoeff
.
BT Product — BT product
0.5
(default)  real scalar in range [0
,
1
]
Specify the BT product as a real scalar in the range
[0
, 1
].
Tunable: Yes
Dependency
To enable this parameter, set Type to
ACPR
and Filter
Shape to Gaussian
.
Programmatic Use
See FilterCoeff
.
Property Inspector Only
Channel Names — Input channel names
[]
(default)  character vector  string  array of strings or character vectors.
Input channel names, specified as a character vector, string, or array. The names appear in
the legend, Settings, and Measurements
panels. If you do not specify the names, the scope labels the channels as
Channel 1
, Channel 2
, etc.
Example: ["A","B"]
Dependency
To see channel names, select Legend in the Analyzer tab.
Programmatic Use
Block Parameter: ChannelNames 
Type: cell array of character vectors or string array 
Maximize Axes — Maximize size of plots
Auto
(default)  Off
 On
Auto
— If you have not specified Title and YLabel, the scope maximizes all plots.On
— The scope maximizes all plots and hides all values in Title and Ylabel.Off
— The scope does not maximize plots.
Hover over the Spectrum Analyzer to see the maximize axes button .
Tunable: Yes
Programmatic Use
Block Parameter: MaximizeAxes 
Type: character vector or string scalar 
Axes Scaling — Yaxis scaling mode
OnceAtStop
(default)  Manual
 Auto
 Updates
OnceAtStop
— Scale yaxis after simulation completes.Manual
— Manually scale yaxis range with the Scale Yaxis Limits toolbar button.Auto
— Scale yaxis range during and after simulation.Updates
— Scale yaxis after the number of time steps specified in the Number of Updates text box (100
by default). Scaling occurs only once during each run.
Tunable: Yes
Programmatic Use
Block Parameter: AxesScaling 
Type: character vector or string scalar 
Number of Updates — Number of updates before scaling
100
(default)  integer
Set this property to delay auto scaling the yaxis.
Tunable: Yes
Dependency
To enable this property, set Axes Scaling to Updates
.
Programmatic Use
Block Parameter: AxesScalingNumUpdates 
Type: character vector or string scalar 
Values: scalar 
Block Characteristics
Data Types 

Direct Feedthrough 

Multidimensional Signals 

VariableSize Signals 

ZeroCrossing Detection 

More About
Cursor Measurements
Measure signal values using vertical waveform cursors that track along the signal.
When you click the Data Cursors button in the Measurements tab of the Spectrum Analyzer, the spectrum display shows vertical cursors on each signal. Each cursor tracks a vertical line along the signal. The scope displays the difference between x and yvalues of the signal at the two cursors in the box between the cursors.
To enable cursor measurements, click the Data Cursors button in the Measurements tab. The cursors appear only when the Spectrum Analyzer has at least one signal in its display.
You can use the mouse to move the vertical cursors left and right.
In the Measurements tab, click the Data Cursors dropdown arrow to select one of these options:
Snap to Data — To position the cursors on the signal data points.
Lock Cursor Spacing — To lock the frequency difference between the two cursors.
For modifying the cursor measurements programmatically, see the CursorMeasurementsConfiguration
object.
Peak Finder Measurements
Compute and display peak values in the scope display.
When you click on the Peak Finder button in the Measurements tab of the Spectrum Analyzer, an arrow appears on the plot at each maxima and a Peaks panel appears at the bottom of the scope window. The Spectrum Analyzer computes peaks from the portion of the input signal that is currently on display in the scope, and the Peaks panel shows the peak values and the frequencies at which they occur.
The Peaks section in the Measurements tab allows you to specify the number of peaks you want the scope to display, the minimum height above which you want the scope to detect peaks, the minimum distance between peaks, and label the peaks.
The Spectrum Analyzer algorithm defines a peak as a local maximum with lower values present on either side of the peak. It does not consider end points as peaks. For more information on the algorithm, see the findpeaks
function.
The peaks are valid for any units of the input signal. The letter after the value associated with each measurement indicates the abbreviation for the appropriate International System of Units (SI) prefix, such as m for milli. For example, if the input signal is measured in volts, an m next to a measurement value indicates that this value is in units of millivolts.
For modifying the peak finder measurements programmatically, see the PeakFinderConfiguration
object. For more information on these settings in the
UI, see Peaks.
Distortion Measurements
Measure harmonic distortion and intermodulation distortion.
When you click the Distortion button in the Distortion section of the Measurements tab, a distortion panel opens at the bottom of the Spectrum Analyzer window. This panel shows the harmonic and distortion measurement values for the input signal currently on display in the scope. The Distortion section in the Measurements tab allows you to specify the distortion type, number of harmonics, and even label the harmonics.
Note
For an accurate measurement, ensure that the fundamental signal (for harmonics) or
primary tones (for intermodulation) is larger than any spurious or harmonic content. To
do so, you may need to adjust the resolution bandwidth (RBW
) of the
Spectrum Analyzer. Make sure that the bandwidth is low enough to isolate the signal and
harmonics from spurious noise content. In general, you should set the RBW value such
that there is at least a 10 dB separation between the peaks of the sinusoids and the
noise floor. You also might need to select a different spectral window to obtain a valid
measurement.
You can set the Distortion Type parameter to one of these values:
Harmonic
–– SelectHarmonic
if your input is a single sinusoid.Intermodulation
–– SelectIntermodulation
if your input is two equalamplitude sinusoids. Intermodulation can help you determine distortion when the scope uses only a small portion of the available bandwidth.
See Distortion Measurements for information on how distortion measurements are calculated.
When you set the Distortion Type to Harmonic
,
these fields appear in the Harmonic Distortion panel at the bottom
of the Spectrum Analyzer window.
H1 — Fundamental frequency in Hz and its power in decibels of the measured power referenced to 1 milliwatt (dBm).
H2, H3, ... — Harmonics frequencies in Hz and their power in decibels relative to the carrier (dBc). If the harmonics are at the same level or exceed the fundamental frequency, reduce the input power.
THD — Total harmonic distortion. This value represents the ratio of the power in the harmonics D to the power in the fundamental frequency S. If the noise power is too high in relation to the harmonics, the THD value is not accurate. In this case, lower the resolution bandwidth or select a different spectral window.
$$THD=10\cdot {\mathrm{log}}_{10}(D/S)$$
SNR — Signaltonoise ratio (SNR). This value represents the ratio of the power in the fundamental frequency S to the power of all nonharmonic content N, including spurious signals, in decibels relative to the carrier (dBc).
$$SNR=10\cdot {\mathrm{log}}_{10}(S/N)$$
If you see
––
as the reported SNR, the total nonharmonic content of your signal is less than 30% of the total signal.SINAD — Signaltonoiseanddistortion ratio. This value represents the ratio of the power in the fundamental frequency S to all other content (including noise N and harmonic distortion D) in decibels relative to the carrier (dBc).
$$SINAD=10\cdot {\mathrm{log}}_{10}\left(\frac{S}{N+D}\right)$$
SFDR — Spuriousfree dynamic range (SFDR). This value represents the ratio of the power in the fundamental frequency S to power of the largest spurious signal R regardless of where it falls in the frequency spectrum. The worst spurious signal might or might not be a harmonic of the original signal. SFDR represents the smallest value of a signal that can be distinguished from a large interfering signal. SFDR includes harmonics.
$$SNR=10\cdot {\mathrm{log}}_{10}(S/R)$$
The harmonic distortion measurement automatically locates the largest sinusoidal component (fundamental signal frequency). It then computes the harmonic frequencies and power in each harmonic in your signal and ignores any DC component. The measurement does not include any harmonics that are outside the Spectrum Analyzer frequency span. Adjust your frequency span so that it includes all the desired harmonics.
Note
To view the best harmonics, make sure that your fundamental frequency is set high enough to resolve the harmonics. However, this frequency should not be so high that aliasing occurs. For the best display of harmonic distortion, your plot should not show skirts, which indicate frequency leakage. The noise floor should be visible.
For a better display, try a Kaiser window with a large sidelobe attenuation (e.g. between 100–300 db).
When you set the Distortion Type to
Intermodulation
, the following fields appear in the
Intermodulation Distortion panel at the bottom of the Spectrum
Analyzer window.
F1 — Lower fundamental firstorder frequency.
F2 — Upper fundamental firstorder frequency.
2F1  F2 — Lower intermodulation product from thirdorder harmonics.
2F2  F1 — Upper intermodulation product from thirdorder harmonics.
TOI — Thirdorder intercept point. If the noise power is too high in relation to the harmonics, the TOI value will not be accurate. In this case, you should lower the resolution bandwidth or select a different spectral window. If the TOI has the same amplitude as the input twotone signal, reduce the power of that input signal.
The intermodulation distortion measurement automatically locates the fundamental and the firstorder frequencies (F1 and F2). It then computes the frequencies of the thirdorder intermodulation products (2F1−F2 and 2F2−F1).
For modifying the distortion measurements programmatically, see the DistortionMeasurementsConfiguration
object. For more information on these
settings in the UI, see Distortion.
Channel Measurements
Measure the occupied bandwidth or adjacent channel power ratio (ACPR).
When you click the Channel Measurements button in the Channel Measurements tab, a channel measurements panel opens at the bottom of the Spectrum Analyzer window. This panel displays the occupied bandwidth or the adjacent channel power ratio measurements. In the Channel Measurements tab, you can specify the occupied bandwidth or the ACPR settings, frequency span, center frequency, and start and stop frequencies.
You can select the channel measurements Type to:
Occupied BW
–– Occupied bandwidthACPR
–– Ratio of the power of the main channel to the power of the adjacent channel
For more details on how the Spectrum Analyzer calculates the occupied bandwidth, see Occupied BW.
Occupied Bandwidth
When you set the Type of channel measurement to compute and display to
Occupied BW
, these fields appear in the measurements panel at
the bottom of the scope window.
Channel Power — Total power in the channel
Occupied BW — Bandwidth containing the specified Occupied BW (%) of the total power of the spectrum.
Frequency Error — Difference between the center of the occupied band and the center frequency (Center Frequency (Hz)) of the channel
ACPR
When you set the Type of channel measurement to compute and display to
ACPR
, these fields appear in the measurements panel at the
bottom of the scope window.
Lower (Rel Power (dBc)) — Ratio of the power of the lower sideband to the power of the main channel
Upper (Rel Power (dBc)) — Ratio of the power of the upper sideband to the power of the main channel
To modify the channel measurements programmatically, see the ChannelMeasurementsConfiguration
object. For more information on these
settings in the UI, see Channel Measurements.
Spectral Mask
Visualize spectrum limits and compare spectrum values to specification values.
Add upper and lower masks to the Spectrum Analyzer to visualize spectrum limits and compare spectrum values to specification values. To enable the Spectral Mask tab, select Spectrum in the Analyzer tab. When you click the Upper Mask and Lower Mask buttons in the Spectral Mask tab, a Spectral Mask panel opens at the bottom of the Spectrum Analyzer window. This panel provides information on passfail statistics of masks, names of masks currently failing or passing, and names of channels causing the failure.
You can modify the mask settings in the Spectral Mask tab. For more
information on these settings in the UI, see Spectral Mask. For
modifying the channel measurements programmatically, see the SpectralMaskConfiguration
object.
You can check the status of the spectral mask using the getSpectralMaskStatus
function. This function gives details on the number
of times a mask succeeded or failed, names of channels causing mask failure, and so
on.
You can even use the MaskTestFailed
event to perform an action every time
the mask fails. To trigger a function when the mask fails, create a listener to the
MaskTestFailed
event and define a callback function to trigger
it. For more details about using events, see Events.
Customize Visualization
Set configuration and style settings in the Spectrum Analyzer.
To control the settings of the display and labels, color and styling, click on Settings () in the Analyzer tab of the Spectrum Analyzer toolstrip.
In the dialog box that opens, you can customize the font size, plot type, yaxis properties of the spectrum plot, and color map properties of the spectrogram plot. You can change the color of the spectrum plot, background, axes, and labels and also change the line properties.
When you view the spectrum or the spectrogram, you see only the relevant options. For more details about these options, see Configuration > Spectrum Settings.
Display Controls
Zoom and pan axes using display controls.
To scale the plot axes, use the mouse to pan around the axes and the scroll button on your mouse to zoom in and out of the plot. Additionally, you can use the buttons that appear when you hover over the plot window.
— Maximize the axes, hide all labels and inset the axes values.
— Zoom in on the plot.
— Pan the plot.
— Autoscale the axes to fit the shown data.
Algorithms
Spectrum Estimation — Filter Bank
When you choose the Filter Bank
method, the Spectrum
Analyzer uses an analysis filter bank to estimate the power spectrum.
The filter bank splits the broadband input signal x(n), of sample rate fs, into multiple narrow band signals y_{0}(m), y_{1}(m), … , y_{M1}(m), of sample rate fs/M.
The variable M represents the number of frequency bands in the
filter bank. In the Spectrum Analyzer, M is equal to the number of
data points needed to achieve the specified RBW value or 1024, whichever is larger. For
more information on the analysis filter bank and its implementation, see the More About and the Algorithm sections in the
dsp.Channelizer
object.
After the Spectrum Analyzer splits the broadband input signal into multiple narrow bands, it computes the power in each narrow frequency band using the following equation. Each Z_{i} value is the power estimate over that narrow frequency band.
$${Z}_{i}=\frac{1}{L}{\displaystyle \sum _{m=0}^{L1}{\left{y}_{i}[m]\right}^{2}}$$
L is length of the narrowband signal y_{i}(m) and i = 1, 2, …, M−1.
The power values in all the narrow frequency bands (denoted by Z_{i}) form the Z vector.
$$Z=[{Z}_{0},\text{\hspace{0.17em}}{Z}_{1},\text{\hspace{0.17em}}{Z}_{2},\cdots ,{Z}_{M1}]$$
The Spectrum Analyzer averages the current Z vector with the previous Z vectors using one of the two moving average methods: video bandwidth or exponential weighting. The output of the averaging operation forms the spectral estimate vector. For details on the two averaging methods, see Averaging Method.
The Spectrum Analyzer uses the value you specify in the RBW (Hz) parameter to determine the input frame length. To view the RBW (Hz) parameter in the scope, click the Analyzer tab on the Spectrum Analyzer toolstrip and navigate to the Bandwidth section.
Spectrum Analyzer requires a minimum number of samples to compute a spectral estimate. This value is directly related to the resolution bandwidth property RBW (Hz).
When you set RBW (Hz) to:
Auto
–– The Spectrum Analyzer requires 1024 samples to update the display. The Spectrum Analyzer determines the appropriate resolution bandwidth to ensure that there are 1024 RBW intervals over the specified frequency span. When you set RBW (Hz) toAuto
, the Spectrum Analyzer calculates RBW using this equation.$$RB{W}_{auto}=\frac{span}{1024}$$
scalar value –– The Spectrum Analyzer calculates the number of samples N_{samples} using this equation.
$${N}_{samples}=\frac{{F}_{s}}{RBW}$$
F_{s} is the sample rate of the input signal as specified in the Sample Rate (Hz) property. To view the Sample Rate (Hz) in the scope, click the Analyzer tab on the Spectrum Analyzer toolstrip and navigate to the Bandwidth section.
When you specify a resolution bandwidth using the RBW (Hz) parameter, you must specify a value such that there are at least two RBW intervals over the specified frequency span. The ratio of the overall span to RBW must be greater than two.
$$\frac{span}{RBW}>2$$
span is the frequency span over which the Spectrum Analyzer
computes and plots the spectrum. To view the Span (Hz) in the
scope, click the Estimation tab on the Spectrum Analyzer toolstrip
and navigate to the Frequency Options section. To enable this
property, set Frequency Span to Span and Center
Frequency
.
When the number of input samples is not sufficient to achieve the specified resolution bandwidth, the Spectrum Analyzer displays a message similar to this one.
The Spectrum Analyzer removes this message and displays a spectral estimate once you provide enough input samples.
Spectrum Estimation — Welch's Method
When you select the Welch
method, the power spectrum estimate is
the averaged modified periodograms.
The algorithm in the Spectrum Analyzer consists of these steps:
The block buffers the input into Npoint data segments. Each data segment is split into P overlapping data segments, each of length M, overlapping by D points. The data segments can be represented as:
$$\begin{array}{l}{x}_{i}(n)=x(n+iD),\text{\hspace{1em}}\text{\hspace{0.05em}}n=0,1,\mathrm{...},M1\\ \text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}\text{\hspace{1em}}i=0,1,\mathrm{...},P1\end{array}$$
If D = M/2, the overlap is 50%.
If D = 0, the overlap is 0%.
Apply a window to each of the P overlapping data segments in the time domain.
The Spectrum Analyzer uses RBW (Hz) in the Analyzer tab to determine the data window length N_{window} internally. Then, it partitions the input signal into a number of windowed data segments.
Most window functions afford more influence to the data at the center of the set than to the data at the edges, which represents a loss of information. To mitigate that loss, the individual data sets are commonly overlapped in time. For each windowed segment, compute the periodogram by computing the discrete Fourier transform. Then compute the squared magnitude of the result and divide the result by M.
$${P}_{xx}^{i}(f)=\frac{1}{MU}{\left{\displaystyle \sum _{n=0}^{M1}{x}_{i}(n)w(n){e}^{j2\pi fn}}\right}^{2},\text{\hspace{1em}}\text{\hspace{1em}}i=0,1,\mathrm{...},P1$$
where U is the normalization factor for the power in the window function and is given by
$$U=\frac{1}{M}{\displaystyle \sum _{n=0}^{M1}{w}^{2}(n)}$$
You can specify the window using the Window parameter in the Estimation tab of the Spectrum Analyzer toolstrip.
The Spectrum Analyzer calculates and plots the power spectrum, power spectrum density, and RMS using the modified Periodogram estimator. For more information about the Periodogram method, see
periodogram
.To determine the power spectrum estimate for Welch's method, the Spectrum Analyzer averages the result of the periodograms for the last P data segments. The averaging reduces the variance, compared to the original Npoint data segment. For more details on the averaging, see Averaging Method.
$$\mathrm{PSD}\left(f\right)=\frac{1}{P}{\displaystyle \sum _{i=0}^{P1}{P}_{xx}^{i}(f)}$$
The Spectrum Analyzer computes the power spectral density using:
$$\mathrm{PSD}\left(f\right)=\frac{1}{P*{F}_{s}}{\displaystyle \sum _{i=0}^{P1}{P}_{xx}^{i}(f)}$$
The power spectrum is the product of the power spectral density and the resolution bandwidth, as given by this equation.
$${P}_{spectrum}\left(f\right)=\mathrm{PSD}\left(f\right)\times RBW=\mathrm{PSD}\left(f\right)\times \frac{{F}_{s}\times NENBW}{{N}_{window}}$$
The Spectrum Analyzer plots the power as a spectrogram in the Spectrogram mode. Each line of the spectrogram is one periodogram. The time resolution of each line is 1/RBW, which is the minimum attainable resolution. Achieving the resolution you want might require combining several periodograms. You then use interpolation to calculate noninteger values of 1/RBW. In the spectrogram display, time scrolls from top to bottom, so the most recent data appears at the top of the display. The offset shows the time value at which the center of the most current spectrogram line occurred.
The Spectrum Analyzer requires a minimum number of samples to compute a spectral estimate. This value is directly related to the resolution bandwidth (RBW).
$${N}_{samples}=\frac{\left(1\frac{{O}_{p}}{100}\right)\times NENBW\times {F}_{s}}{RBW}$$
where O_{p} is the overlap percentage, NENBW is the normalized effective noise bandwidth, F_{s} is the input sample rate, and RBW is the resolution bandwidth.
The Spectrum Analyzer shows the number of samples per update in the Spectrum Analyzer status bar.
You can enable Samples/Update
in the status bar only when you set
Input Domain to Time
and
Method to Welch
in the
Estimation tab on the Spectrum Analyzer toolstrip.
Overlap Percentage (O_{p})
The overlap percentage O_{p} is the value you specify in the Overlap % property. To view the Overlap % in the scope, click the Estimation tab on the Spectrum Analyzer toolstrip and navigate to the Window Options section.
When you increase the overlap percentage, the Spectrum Analyzer needs fewer new input samples to compute a new spectral update.
O_{p}  N_{samples} 

0%  100 
50%  50 
80%  20 
Normalized Effective Noise Bandwidth (NENBW)
The normalized effective noise bandwidth NENBW is a window parameter that measures the noise performance of the window. NENBW is determined using the window length and the window coefficients, and is given by the following equation:
$$NENBW={N}_{window}\times \frac{{\displaystyle \sum _{n=1}^{{N}_{window}}{w}^{2}(n)}}{{\left[{\displaystyle \sum _{n=1}^{{N}_{window}}w(n)}\right]}^{2}}$$
w(n) denotes the vector of window coefficients (calculated internally). N_{window} is the window length the Spectrum Analyzer needs to compute one spectral update, and is directly related to the resolution bandwidth and normalized effective noise bandwidth.
$${N}_{window}=\frac{NENBW\times {F}_{s}}{RBW}$$
The rectangular window has the smallest NENBW, with a value of 1. All other windows have a larger NENBW value. For example, the Hann window has an NENBW value of approximately 1.5.
The Spectrum Analyzer shows the value of NENBW in the Spectrum Analyzer status bar.
You can enable NENBW
only when you set Input
Domain to Time
and Method
to Welch
in the Estimation tab on the
Spectrum Analyzer toolstrip.
Input Sample Rate (Fs)
F_{s} is the sample rate of the input signal.
To view the Sample Rate (Hz) in the scope, click the
Analyzer tab on the Spectrum Analyzer toolstrip and navigate to
the Bandwidth section. You can enable this property in the status
bar at the bottom of the Spectrum Analyzer window. Rightclick the status bar and select
Sample Rate
.
Resolution Bandwidth (RBW)
Resolution bandwidth controls the spectral resolution of the displayed signal. The RBW value determines the spacing between frequencies that the scope can resolve. A smaller value gives a higher spectral resolution and lowers the noise floor, that is, the Spectrum Analyzer can resolve frequencies that are closer to each other. However, this comes at the cost of a longer sweep time.
You can set the resolution bandwidth through the RBW (Hz) property. To view RBW (Hz) in the scope, click the Analyzer tab on the Spectrum Analyzer toolstrip and navigate to the Bandwidth section.
When you set RBW (Hz) to:
Auto
–– The Spectrum Analyzer requires 1024 samples to update the display. The Spectrum Analyzer determines the appropriate resolution bandwidth to ensure that there are 1024 RBW intervals over the specified frequency span. When you set RBW (Hz) toAuto
, the Spectrum Analyzer calculates using this equation.$$RB{W}_{auto}=\frac{span}{1024}$$
scalar value –– Specify a value such that there are at least two RBW intervals over the specified frequency span. The ratio of the overall span to RBW must be greater than two:
$$\frac{span}{RBW}>2$$
span is the frequency span over which the Spectrum Analyzer
computes and plots the spectrum. Spectrum Analyzer shows the span through the
Span (Hz) property. To view the Span (Hz)
in the scope, click the Estimation tab on the Spectrum Analyzer
toolstrip, navigate to the Frequency Options section, and set
Frequency Span to Span and Center
Frequency
.
When the number of input samples is not sufficient to achieve the specified resolution bandwidth, the Spectrum Analyzer displays a message similar to this one.
The Spectrum Analyzer removes this message and displays a spectral estimate once you provide enough input samples.
You can enable this property in the status bar at the bottom of the Spectrum Analyzer
window. Rightclick the status bar and select RBW
.
Nyquist Frequency Interval
When you plot the twosided spectrum by selecting TwoSided Spectrum in the Spectrum or Spectrogram tab, the Nyquist frequency interval is $$\left[\frac{SampleRate}{2},\frac{SampleRate}{2}\right]+FrequencyOffset$$ Hz.
When you clear the TwoSided Spectrum, the Nyquist frequency interval is $$\left[0,\frac{SampleRate}{2}\right]+FrequencyOffset$$ Hz.
Frequency Vector
When you set Frequency (Hz) to Auto
, the software calculates the frequency vector for the frequencydomain input.
When you plot the twosided spectrum by selecting TwoSided Spectrum in the Spectrum or Spectrogram tab, the frequency vector is:
$$\left[\frac{SampleRate}{2},\frac{SampleRate}{2}\right]$$
When you clear the TwoSided Spectrum, the frequency vector is:
$$\left[0,\frac{SampleRate}{2}\right]$$
Occupied BW
The Spectrum Analyzer calculates Occupied BW using these steps.
Calculate the total power in the measured frequency range.
Determine the lower frequency value. Starting at the lowest frequency in the range and moving upward, sum the power distributed in each frequency until the result is
$$\frac{100OccupiedBW\%}{2}$$
of the total power.
Determine the upper frequency value. Starting at the highest frequency in the range and moving downward, sum the power distributed in each frequency until the result reaches
$$\frac{100OccupiedBW\%}{2}$$
of the total power.
The bandwidth between the lower and upper power frequency values is the occupied bandwidth.
The frequency halfway between the lower and upper frequency values is the center frequency.
Distortion Measurements
The Spectrum Analyzer calculates Distortion Measurements using these steps.
Estimate spectral content by finding peaks in the spectrum. When the algorithm detects a peak, it records the width of the peak and clears all monotonically decreasing values by treating all these values as if they belong to the peak. Using this method, the algorithm removes all spectral content centered at DC (0 Hz) from the spectrum and records the amount of bandwidth cleared (W_{0}).
Determine the fundamental power (P_{1}) from the remaining maximum value of the displayed spectrum. Create a local estimate (Fe_{1}) of the fundamental frequency by computing the central moment of the power near the peak. Record the bandwidth of the fundamental power content (W_{1}). Then remove the power from the fundamental as in step 1.
Determine the power and width of the higherorder harmonics (P_{2}, W_{2}, P_{3}, W_{3}, etc.) in succession by examining the frequencies closest to the appropriate multiple of the local estimate (Fe_{1}). Remove any spectral content that decreases monotonically about the harmonic frequency from the spectrum before proceeding to the next harmonic.
After removing the DC, fundamental, and harmonic content from the spectrum, examine the power of the remaining spectrum for its sum (P_{remaining}), peak value (P_{maxspur}), and median value (P_{estnoise}).
Compute the sum of all the removed bandwidth as W_{sum} = W_{0} + W_{1} + W_{2} +...+ W_{n}.
Compute the sum of powers of the second and higherorder harmonics as P_{harmonic} = P_{2} + P_{3} + P_{4} +...+ P_{n}.
Estimate the sum of the noise power as:
$${P}_{noise}=({P}_{remaining}\cdot dF+{P}_{est.noise}\cdot {W}_{sum})/RBW$$
Where dF is the absolute difference between frequency bins, and RBW is the resolution bandwidth of the window.
Then compute the metrics for THD, THD%, SINAD, SNR, and SFDR from the estimates.
$$\begin{array}{l}THD=10\cdot {\mathrm{log}}_{10}\left(\frac{{P}_{harmonic}}{{P}_{1}}\right)\\ THD\%={100.10}^{\left(THD/20\right)}\\ SINAD=10\cdot {\mathrm{log}}_{10}\left(\frac{{P}_{1}}{{P}_{harmonic}+{P}_{noise}}\right)\\ SNR=10\cdot {\mathrm{log}}_{10}\left(\frac{{P}_{1}}{{P}_{noise}}\right)\\ SFDR=10\cdot {\mathrm{log}}_{10}\left(\frac{{P}_{1}}{\mathrm{max}\left({P}_{maxspur},\mathrm{max}\left({P}_{2},{P}_{3},\mathrm{...},{P}_{n}\right)\right)}\right)\end{array}$$
Harmonic Measurements
The harmonic distortion measurements use the spectrum trace shown in the display as the input to the measurements. The default
Hann
window setting of the Spectrum Analyzer might exhibit leakage that can completely mask the noise floor of the measured signal.The harmonic measurements attempt to correct for leakage by ignoring all frequency content that decreases monotonically away from the maximum of harmonic peaks. If the window leakage covers more than 70% of the frequency bandwidth in your spectrum, you may see a blank reading (–) reported for SNR and SINAD. If your application can tolerate the increased equivalent noise bandwidth (ENBW), consider using a Kaiser window with a high attenuation (up to 330 dB) to minimize spectral leakage.
Ignore the DC component.
After windowing, the width of each harmonic component masks the noise power in the neighborhood of the fundamental frequency and harmonics. To estimate the noise power in each region, the Spectrum Analyzer computes the median noise level in the nonharmonic areas of the spectrum. It then extrapolates that value into each region.
N^{th} order intermodulation products occur at A*F1 + B*F2,
where F1 and F2 are the sinusoid input frequencies and A + B = N. A and B are integer values.
For intermodulation measurements, compute the thirdorder intercept (TOI) point as follows.
TOI_{lower} = P_{F1} + (P_{F2}  P_{(2F1F2)})/2
TOI_{upper} = P_{F2} + (P_{F1}  P_{(2F2F1)})/2
TOI = + (TOI_{lower} + TOI_{upper})/2
Where P is power in decibels of the measured power referenced to 1 milliwatt (dBm).
Averaging Method
The Spectrum Analyzer can calculate the moving average using two methods:
Video bandwidth — The Spectrum Analyzer uses a timedomain lowpass filter to smooth the noise in the signal. The video bandwidth (VBW) filter smoothes the trace and decreases noise, and the Spectrum Analyzer applies the filter to the data before displaying it.
Video bandwidth is the bandwidth of the lowpass filter that Spectrum Analyzer uses to average or smooth the noise in the signal before displaying it in the scope. The Spectrum Analyzer computes the video bandwidth using this equation:
$$VBW=\frac{(1\lambda )RBW}{2\pi \lambda NENBW}$$
where,
Video bandwidth does not affect the level of the noise (noise floor), but only increases the signaltonoise ratio and smoothes the trace of the noise. When you decrease the value of VBW, the signaltonoise ratio improves.
The cutoff frequency of the video bandwidth filter is given by:
$${\omega}_{c}=\frac{2\pi VBW}{{F}_{s}/NFFT}$$
where Fs is the input sample rate and NFFT is the number of FFT points.
The Spectrum Analyzer shows the values of sample rate, VBW, and NFFT in the status bar at the bottom of the display. To enable, rightclick the status bar and select
Sample Rate
,VBW
, andNFFT
.Exponential — The moving average algorithm uses the exponential weighting method to update the weights and compute the moving average recursively for each Z vector that comes in by using the following recursive equations:
$$\begin{array}{l}{w}_{N}=\lambda {w}_{N1}+1\\ {\overline{z}}_{N}=\left(1\frac{1}{{w}_{N}}\right){\overline{z}}_{N1}+\left(\frac{1}{{w}_{N}}\right){z}_{N}\end{array}$$
λ — Forgetting factor
$${w}_{N}$$ — Weighting factor applied to the current Z vector
$${z}_{N}$$ — Current Z vector
$${\overline{z}}_{N1}$$ — Moving average until the previous Z vector
$$\left(1\frac{1}{{w}_{N}}\right){\overline{z}}_{N1}$$ — Effect of the previous Z vectors on the average
$${\overline{z}}_{N}$$ — Moving average including the current Z vector
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.
This block can be used for simulation visibility in systems that generate code, but is not included in the generated code.
HDL Code Generation
Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.
This block can be used for simulation visibility in subsystems that generate HDL code, but is not included in the hardware implementation.
PLC Code Generation
Generate Structured Text code using Simulink® PLC Coder™.
This block can be used for simulation visibility in systems that generate PLC code, but is not included in the generated code.
FixedPoint Conversion
Design and simulate fixedpoint systems using FixedPoint Designer™.
This block accepts fixedpoint input, but converts it to double
for display.
Version History
Introduced in R2014bR2023b: Spectrum Analyzer supports dBuV
units
You can set Spectrum Unit to dBuV
when you set:
Input Domain to
Time
and Spectrum toRMS
.Input Domain to
Frequency
.
You can set Input Unit to dBuV
when you set Input Domain to
Frequency
.
R2023a: Spectrum Analyzer with improved responsiveness and toolstrip interface in Simulink
In R2023a, the Spectrum Analyzer block is more responsive and its
toolstrip interface is improved to provide you easy access to spectral analysis,
estimation, and measurements. You can configure and display Spectrum Analyzer
settings from the command line with the SpectrumAnalyzerConfiguration
object.
See Also
Objects
Functions
Blocks
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