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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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Presentation Transcript
another oscilloscope
Another Oscilloscope???
  • Like an oscilloscope
  • Oscilloscope in time domain
  • Spectrum analyzer in frequency domain (selectable)
is frequency domain better
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
what does sa do
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…
types of rf spectrum analyzer
Types of RF Spectrum Analyzer

Two common ways to measure RF signals

  • Fourier Transform
  • Swept-Tuned or Swept-Toned
fourier analyzer
Fourier Analyzer
  • Capture time domain signals information
  • Digitizes time domain signal (digital sampling)
  • Perform Fourier transform
  • Fast, but limits in frequency range, sensitivity
swept analyzer
Swept Analyzer
  • “Sweep” across frequency range
  • Display the frequency of interest
  • Large frequency range
  • Widely used
rf spectrum analyzer
RF Spectrum Analyzer
  • ADVANTEST 9 kHz to 3 GHz, 1 kHz resolution
three primary function keys
Three Primary Function Keys
  • Frequency (Hz)
  • Amplitude (Abs dBm, Rel dB)
  • Span (Hz) -> (how big the “window” we want to view)
other important keys
Other Important Keys

Auto Tune

Save

Softkeys

Resolution Bandwidth

Video Bandwidth

Peak Search Marker

functions
Functions
  • An instrument for observing a waveform both in time and frequency domains
  • In time domain works as a digital oscilloscope
main keys
Main Keys

Cursor

Measure

Autoset

Sec/Div

Volts/Div

Math

frequency domain
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
taking fft
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

taking fft17
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
taking fft18
Taking FFT
  • Choose the window type
    • Choose the HANNING window for measurements

Point by point

multiplication

=

X

taking fft19
Taking FFT
  • Use FFT Zoom menu to zoom
    • The left graticule line is at 0Hz frequency
measurements scales
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
references
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)