Содержание
- 2. Accurately Detect a Tone What is the exact frequency and amplitude of a tone embedded in
- 3. Presentation Overview Why use the frequency domain? FFT – a short introduction Frequency interpolation Improvements using
- 4. Clean Single Tone Measurement Clean sine tone Easy to measure Clean tone spectrum
- 5. Noisy Tone Measurement Noisy signal Difficult to measure in the time domain Noisy signal spectrum Easier
- 6. Fast Fourier Transform (FFT) Fundamentals (Ideal Case) The tone frequency is an exact multiple of the
- 7. FFT Fundamentals (Realistic Case) The tone frequency is not a multiple of the frequency resolution
- 8. Input Frequency Hits Exactly a Bin Only one bin is activated
- 9. Input Frequency is +0.01 Bin “off” More bins are activated
- 10. Input Frequency is +0.25 Bin “off”
- 11. Input Frequency is +0.50 Bin “off” Highest side-lobes
- 12. Input Frequency is +0.75 Bin “off” The Side lobe levels decrease
- 13. Input Frequency is +1.00 Bin “off” Only one bin is activated
- 14. The Envelope Function
- 15. The Mathematics Envelope function: Bin offset: Real amplitude:
- 16. Demo Amplitude and frequency detection by Sin(x) / x interpolation
- 17. Aliasing of the Side-Lobes
- 18. Weighted Measurement Apply a Window to the signal
- 19. Weighted Spectrum Measurement Apply a Window to the Signal 20 -60 -40 -20 0 25 0
- 20. Rectangular and Hanning Windows Side lobes for Hanning Window are significantly lower than for Rectangular window
- 21. Input Frequency Exactly Hits a Bin Three bins are activated
- 22. Input Frequency is +0.25 Bin “off” More bins are activated
- 23. Input Frequency is +0.50 Bin “off” Highest side-lobes
- 24. Input Frequency is +0.75 Bin “off” The Side lobe levels decrease
- 25. Input Frequency is +1.00 Bin “off” Only three bins activated
- 26. The Mathematics for Hanning ... Envelope: Bin Offset: Amplitude:
- 27. A LabVIEW Tool Tone detector LabVIEW virtual instrument (VI)
- 28. Demo Amplitude and frequency detection using a Hanning Window (named after Von Hann) Real world demo
- 29. Frequency Detection Resolution
- 30. Amplitude Detection Resolution
- 31. Phase Detection Resolution
- 32. Conclusions Traditional counters resolve 10 digits in one second FFT techniques can do this in much
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