Table of Contents
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USER GUIDE
NI Spectral Measurements Toolkit
Contents
This document explains how to use the NI Spectral Measurements Toolkit
(SMT) in LabVIEW and LabWindows
measurements.
Conventions ............................................................................................ 2
Using the Spectral Measurements Toolkit .............................................. 3
Integrating the Spectral Measurements Toolkit............................... 4
Locating the Spectral Measurements Toolkit .................................. 4
SMT Programming Flow Diagram ......................................................... 5
Advanced-Level VIs ........................................................................ 6
Using LabVIEW Spectral Measurements Examples .............................. 7
SMT Simulation Examples .............................................................. 7
SMT Spectrum Analyzer (simulated)....................................... 7
SMT ACP (simulated) .............................................................. 8
Using LabWindows/CVI Spectral Measurements Examples ................. 9
Continuous Zoom FFT..................................................................... 9
Frequency Response Measurement ................................................. 9
Cross Power Spectrum Measurement .............................................. 10
Using Spectral Measurements Toolkit Techniques ................................ 10
Zoom FFT ........................................................................................ 10
Continuous Zoom FFT..................................................................... 12
Block Zoom FFT ............................................................................. 14
Determining When to Use Continuous or Block Zoom FFT........... 14
Zoom Spectrogram .......................................................................... 15
Configuring Zoom FFT VIs.................................................................... 18
Center Frequency and Span ............................................................. 18
Resolution Bandwidth, Spectral Lines, and Window ...................... 20
Choosing Useful Configuration Parameters .................................... 22
Spectral Domain Averaging.................................................................... 24
Averaging Conventions ................................................................... 25
Averaging Options ........................................................................... 26
Averaged FFT Spectrum.................................................................. 27
Averaged Power Spectrum .............................................................. 28
™
™
/CVI
for frequency-domain
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Summary of Contents for National Instruments NI Spectral Measurements Toolkit
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Page 1: Table Of Contents
USER GUIDE NI Spectral Measurements Toolkit This document explains how to use the NI Spectral Measurements Toolkit (SMT) in LabVIEW and LabWindows measurements. Contents Conventions ... 2 Using the Spectral Measurements Toolkit ... 3 SMT Programming Flow Diagram ... 5 Using LabVIEW Spectral Measurements Examples ... -
Page 2: Conventions
Italic text in this font denotes text that is a placeholder for a word or value monospace italic that you must supply. NI Spectral Measurements Toolkit User Guide Averaged Cross Spectrum ...28 Averaged Frequency Response ...29 Unit Conversion...29 Peak Search and Amplitude/Frequency Estimation ...31... -
Page 3: Using The Spectral Measurements Toolkit
LabVIEW. Analog modulation—The Spectral Measurements Toolkit supports analog modulation to perform amplitude, frequency, and phase modulation and demodulation. Functions and VIs are included to perform upconversion and downconversion on baseband and passband signals. NI Spectral Measurements Toolkit User Guide... -
Page 4: Integrating The Spectral Measurements Toolkit
For more information about supported hardware, refer to the NI Spectral Measurements Toolkit Readme, located at Start»All Programs»National Instruments» Spectral Measurements. For simplicity, this document pertains only to using VIs in the LabVIEW... -
Page 5: Smt Programming Flow Diagram
Enter the time-domain data into the SMT Basic Zoom Power Spectrum VI. This VI specifies the zoom settings in terms of only center frequency and span. The VI performs zoom FFT processing and returns a power spectrum in units V NI Spectral Measurements Toolkit User Guide... -
Page 6: Advanced-Level Vis
Complete the following steps when using the advanced-level VIs of the programming flow diagram in the SMT Programming Flow VI: NI Spectral Measurements Toolkit User Guide Enter the output power spectrum into an SMT measurement VI and/or use the SMT Spectrum Unit Conversion VI as follows:... -
Page 7: Using Labview Spectral Measurements Examples
4.96 MHz and the resolution bandwidth as 30.88 kHz. © National Instruments Corporation Using LabWindows/CVI Spectral section. folder contains examples that are hardware-independent Simulation < LabVIEW >\ folder. If you are folder inside the Simulation folder. NI Spectral Measurements Toolkit User Guide... -
Page 8: Smt Acp (Simulated)
Perform the adjacent channel power measurement on an unscaled power spectrum Note before calling the SMT Spectrum Unit Conversion VI. NI Spectral Measurements Toolkit User Guide Averaging type, such as vector averaging, RMS averaging, or peak hold Weighting type, such as linear or exponential... -
Page 9: Using Labwindows/Cvi Spectral Measurements Examples
The example uses handles to maintain state information between functions, such as © National Instruments Corporation < LabWindows/CVI >\samples\smt folder contains examples that use a simulated source. Use simulated SmtConfigZoomFFT folder. You samples\smt\ samples\ SmtZoomFFT NI Spectral Measurements Toolkit User Guide... -
Page 10: Cross Power Spectrum Measurement
The standard FFT, shown in the upper graph, indicates a single peak, and the zoom FFT, shown in the lower graph, indicates the presence of two separate tones in the signal. NI Spectral Measurements Toolkit User Guide samples\ ni.com... - Page 11 Figure 2. Zoom FFT Technique df = f /N = 1/T is the frequency of the sampled signal T is the time duration N is the number of samples or increase N to improve df. NI Spectral Measurements Toolkit User Guide...
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Page 12: Continuous Zoom Fft
The continuous zoom FFT shifts a high-frequency signal into the baseband before adjusting the sample rate. NI Spectral Measurements Toolkit User Guide /M. The antialias filter has a cutoff /(2 × M) because the Nyquist frequency has decreased by... - Page 13 © National Instruments Corporation 15.0m 14.0m 12.0m 10.0m 8.0m 6.0m 4.0m 2.0m –2.0m –4.0m –6.0m –8.0m –10.0m –12.0m –14.0m –15.0m –15.0m –10.0m –5.0m Figure 4. I/Q Plot 1.7a 5.0m 10.0m 15.0m I (Volts) NI Spectral Measurements Toolkit User Guide...
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Page 14: Block Zoom Fft
VI, either reduce the acquisition rate or use the block zoom technique. NI Spectral Measurements Toolkit User Guide updates like a block zoom FFT and waits for the VI by reusing the last half of the... -
Page 15: Zoom Spectrogram
FFT on the windowed segment, and arranges the resulting FFTs in chronological order. Figure 5 illustrates the process. Note STFT VIs are located in the Measurements Toolset © National Instruments Corporation < LabVIEW >\vi.lib\addons\Spectral folder. NI Spectral Measurements Toolkit User Guide... - Page 16 The VI also has advanced parameters for specifying the spectrogram, including window, resolution bandwidth, RBW definition, frequency points, time points, and NI Spectral Measurements Toolkit User Guide Time Span Time (µ s ) Figure 5.
- Page 17 Figure 6 shows an example of a completed spectrogram with a center frequency of 16 MHz and a span of 16 MHz. Figure 6. Spectrogram Example © National Instruments Corporation NI Spectral Measurements Toolkit User Guide...
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Page 18: Configuring Zoom Fft Vis
• • • NI Spectral Measurements Toolkit User Guide center frequency must fall within the effective band of the input signal. The effective band is the frequency band in which the data from the input signal is valid. You can use the effective band to exclude the roll-off region of an analog antialiasing filter from consideration. - Page 19 Figure 7b demonstrates that if you enter a center frequency value © National Instruments Corporation Antialiasing Filter Response Span Figure 7. Center Frequency and Span Combinations Coerced Result Effective Band Span Effective Band Span = (f Effective Band Span Effective Band Span NI Spectral Measurements Toolkit User Guide...
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Page 20: Resolution Bandwidth, Spectral Lines, And Window
The default value of RBW definition is 3 dB. NI Spectral Measurements Toolkit User Guide Figure 8. Main and Side Lobes of a 7-Term Blackman-Harris Window ni.com... - Page 21 © National Instruments Corporation acquisition size = 2 × spectral lines × zoom factor zoom factor 3 dB BW acquisition size ----------------------------------- - NI Spectral Measurements Toolkit User Guide 2 ⁄ ---------- - span ×...
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Page 22: Choosing Useful Configuration Parameters
The choice of RBW depends on a number of factors, such as the spacing between the two tones that you want to identify and the amplitude of these tones. NI Spectral Measurements Toolkit User Guide df = f /N = 1/T... - Page 23 © National Instruments Corporation Table 1. Larger versus Smaller RBW Smaller RBW (9.94 kHz) Larger FFT size, requiring more computation time Can distinguish between the two tones in the spectrum Figure 9. RBW Example NI Spectral Measurements Toolkit User Guide...
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Page 24: Spectral Domain Averaging
When you apply a zoom FFT VI to a signal, you receive the complex FFT spectrum. The spectrum domain averaging functions can operate on the FFT spectrum to return different types of spectra, such as averaged FFT spectrum, power spectrum, cross spectrum, and frequency response. NI Spectral Measurements Toolkit User Guide ni.com... -
Page 25: Averaging Conventions
X and its averaged output Y. Each complex frequency of spectrum X in magnitude to its counterpart in Y is retained. The result is a real spectrum. Complex conjugate. is compared . The larger value NI Spectral Measurements Toolkit User Guide... -
Page 26: Averaging Options
For linear weighting, For exponential weighting, where N is a user-specified constant that determines how much weight is given to recent data relative to older data. Small values of N place more NI Spectral Measurements Toolkit User Guide Peak-Hold Linear Auto Restart... -
Page 27: Averaged Fft Spectrum
Moving average—Average the most recent N measurements. Continuous—Average all measurements taken with equal weight. Table 2. FFT Averaging Methods and Equations Averaging Method Equation = <X> <X conj X ( )> = max(X k – 1 NI Spectral Measurements Toolkit User Guide... -
Page 28: Averaged Power Spectrum
A cross spectrum has no peak-hold average. NI Spectral Measurements Toolkit User Guide Table 3. Averaged Power Spectrum Averaging Methods and Equations Averaging Method = conj(X) × Y = <... -
Page 29: Averaged Frequency Response
© National Instruments Corporation Table 4. Averaged Frequency Response Settings and Equations Setting NI Spectral Measurements Toolkit User Guide -- - Equation H = <Yconj(X)> / <X conj(X)> H = <Y>/<X>... - Page 30 ----------- - ⎝ ⎠ NI Spectral Measurements Toolkit User Guide RMS or peak—An FFT returns an amplitude spectrum scaled such that a frequency bin represents the RMS value of a sine wave at that frequency. A bin can also represent the peak value if you scale the spectrum by Amplitude or power—The power spectrum is the squared magnitude...
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Page 31: Peak Search And Amplitude/Frequency Estimation
FFT bin by Δ. 1 Amplitude 2 Window Shape © National Instruments Corporation 3 Threshold 4 Two FFT Bins Figure 11. Amplitude/Frequency Estimation Algorithm NI Spectral Measurements Toolkit User Guide... -
Page 32: Power In Band
You can use the SMT Adjacent Channel Power (Advanced) VI to measure power for an arbitrary number of adjacent channels at user-specified bandwidths and offsets from the center frequency. NI Spectral Measurements Toolkit User Guide . Perform this measurement before ∑... -
Page 33: Occupied Bandwidth (Obw)
The SMT Occupied Bandwidth VI is appropriate only for single-channel measurements, such as measurements on signals limited to a single frequency band. For multiple-channel measurements, perform each single-channel measurement separately. © National Instruments Corporation Figure 12. ACP Measurement NI Spectral Measurements Toolkit User Guide... -
Page 34: Where To Go For Support
1% of the signal power is actually located there. Where to Go for Support The National Instruments Web site is your complete resource for technical support. At troubleshooting and application development self-help resources to email and phone assistance from NI Application Engineers. - Page 35 Instruments trademarks. Other product and company names mentioned herein are trademarks or trade names of their respective companies. For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txt file on your media, or ni.com/patents.
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