Transcript Spectrum Analyzer - School of Engineering Science

Spectrum Analyzer
Another Oscilloscope???
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Like an
oscilloscope
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Oscilloscope in
time domain
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Spectrum
analyzer in
frequency domain
(selectable)
Is Frequency Domain Better?
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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?
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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
Two common ways to measure RF signals
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Fourier Transform
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Swept-Tuned or Swept-Toned
Fourier Analyzer
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Capture time domain signals information
Digitizes time domain signal (digital sampling)
Perform Fourier transform
Fast, but limits in frequency range, sensitivity
Swept Analyzer
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“Sweep” across frequency range
Display the frequency of interest
Large frequency range
Widely used
RF Spectrum Analyzer
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ADVANTEST 9 kHz to 3 GHz, 1 kHz resolution
Three Primary Function Keys
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Frequency (Hz)
Amplitude (Abs dBm, Rel dB)
Span (Hz) -> (how big the “window” we want to
view)
Other Important Keys
Auto Tune
Save
Softkeys
Peak Search Marker
Resolution Bandwidth
Video Bandwidth
Typical Output Displayed
The TDS-220 Tektronix
Oscilloscope and the
FFT module
7/16/2015
Functions
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An instrument for observing a waveform
both in time and frequency domains
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In time domain works as a digital
oscilloscope
Main Keys
Cursor
Measure
Autoset
Volts/Div
Math
Sec/Div
Frequency Domain
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Takes the FFT of a waveform
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The FFT samples relate to the DTFS samples,
i.e., ak ' s
Takes a portion of a signal and repeats it
Taking FFT
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There 4 steps to take the FFT
1. 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 FFT
•
2.
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 FFT
3.
Choose the window type
•
Choose the HANNING window for measurements
Point by point
multiplication
X
=
Taking FFT
4. Use FFT Zoom menu to zoom
• The left graticule line is at 0Hz frequency
Measurements Scales
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Measurements on FFT waveforms
• Frequency in Hz from 0Hz to half of the sampling
rate
• Magnitude in dB where 0dB equals 1 V RMS
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dB and dBm
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dB a relative value
dBm an absolute value when the reference power is
1mW
References
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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
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TDS200 Series Digital Real-Time
Oscilloscope, User Manual (Tektronix)
TDS200 Series Extension Modules,
Instruction Manual (Tektronix)