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Spectrum Analyzer

Spectrum Analyzer. Another Oscilloscope???. Like an oscilloscope Oscilloscope in time domain Spectrum analyzer in frequency domain (selectable). Is Frequency Domain Better?. In time domain, all frequency components of signals are summed together

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Spectrum Analyzer

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  1. Spectrum Analyzer

  2. Another Oscilloscope??? • Like an oscilloscope • Oscilloscope in time domain • Spectrum analyzer in frequency domain (selectable)

  3. Is Frequency Domain Better? • In time domain, all frequency components of signals are summed together • In freq domain, complex signals are separated into their frequency components

  4. What does SA do? • Processes the signal • Displays the spectral content of the input signal within a selected range of frequencies • i.e., signal power(db) versus frequency • Measures frequency, power, harmonic content, modulation, spurs, and noise, etc…

  5. Types of RF Spectrum Analyzer Two common ways to measure RF signals • Fourier Transform • Swept-Tuned or Swept-Toned

  6. Fourier Analyzer • Capture time domain signals information • Digitizes time domain signal (digital sampling) • Perform Fourier transform • Fast, but limits in frequency range, sensitivity

  7. Swept Analyzer • “Sweep” across frequency range • Display the frequency of interest • Large frequency range • Widely used

  8. RF Spectrum Analyzer • ADVANTEST 9 kHz to 3 GHz, 1 kHz resolution

  9. Three Primary Function Keys • Frequency (Hz) • Amplitude (Abs dBm, Rel dB) • Span (Hz) -> (how big the “window” we want to view)

  10. Other Important Keys Auto Tune Save Softkeys Resolution Bandwidth Video Bandwidth Peak Search Marker

  11. Typical Output Displayed

  12. The TDS-220 Tektronix Oscilloscope and the FFT module

  13. Functions • An instrument for observing a waveform both in time and frequency domains • In time domain works as a digital oscilloscope

  14. Main Keys Cursor Measure Autoset Sec/Div Volts/Div Math

  15. Frequency Domain • Takes the FFT of a waveform • The FFT samples relate to the DTFS samples, i.e., • Takes aportion of a signal and repeats it

  16. Taking FFT • There 4 steps to take the FFT • Setting up the time-domain waveform • Use AUTOSET to display the proper YT waveform • Need to see a few periods of the waveform clearly Good scale Bad scale

  17. Taking FFT • Be careful about the DC values • Press the MATH key to see the FFT menu • Use the FFT CH1/2 to switch between the channel ½ FFT and YT waveforms

  18. Taking FFT • Choose the window type • Choose the HANNING window for measurements Point by point multiplication = X

  19. Taking FFT • Use FFT Zoom menu to zoom • The left graticule line is at 0Hz frequency

  20. Measurements Scales • Measurements on FFT waveforms • Frequency in Hz from 0Hz to half of the sampling rate • Magnitude in dB where 0dB equals 1 V RMS • dB and dBm • dB a relative value • dBm an absolute value when the reference power is 1mW

  21. References • Basic Spectrum Analyzer (HP) • Knowing The Signal Classes Greatly Simplifies Spectrum Analysis (TestMart) • Signal Processing http://www.ece.queensu.ca/hpages/courses/Elec421/why.html • TDS200 Series Digital Real-Time Oscilloscope, User Manual (Tektronix) • TDS200 Series Extension Modules, Instruction Manual (Tektronix)

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