what do these and…jaegerh/phy131/week08-we.pdf · week08.ppt author: herbert jaeger created date:...
TRANSCRIPT
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Spring 2006 – Week 8 PHY 131 5
What do these and…
Spring 2006 – Week 8 PHY 131 6
… these have in common?
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Spring 2006 – Week 8 PHY 131 7
What do these and ….
Spring 2006 – Week 8 PHY 131 8
...these have in common?
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Spring 2006 – Week 8 PHY 131 9
Building Blocks for Periodic Waveforms
Sine-function
Cosine-function
Spring 2006 – Week 8 PHY 131 10
Spectrum Synthesis (a.k.a. Fourier Synthesis)
Any periodic waveform can be expressed as asum of sine and cosine functions of harmonics:
x(t) = ao2+ a1 cos(2π ft) + a2 cos(2π2 ft) + a3 cos(2π 3 ft) + ...
+ b1 sin(2π ft) + b2 sin(2π2 ft) + b3 sin(2π 3 ft) + ... Pattern: only multiples of the fundamentalfrequency f are needed!
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Spring 2006 – Week 8 PHY 131 11
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-4
-2
0
20 1.05 2.1 3.15 4.2 5.25 6.3
Wave1
Wave2
Adding Waveforms
+ = + = – = =
Pick a point on onewaveform and determine itsvalue
Determine the value of theequivalent point on the otherwaveform
Add the values of bothwaveforms to find one pointof the sum waveform
-8
-6
-4
-2
0
20 1.05 2.1 3.15 4.2 5.25 6.3
Wave1
Wave2
Sum
Spring 2006 – Week 8 PHY 131 12
Examples of Spectrum Synthesis
• Manually, using a spreadsheet
• Using a Java Applethttp://projects.cbe.ab.ca/sss/science/physics/map_north/applets/fourier/fouriersynthesis.html
• Another Java Applethttp://www.falstad.com/fourier/
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Spring 2006 – Week 8 PHY 131 13
Spectrum Analysis (a.k.a. Fourier Analysis)
The Process is reversible. Given a periodicwaveform x(t) we can figure out how much ofeach f how many of its harmonics need to beused to reproduce this waveform.
x(t) = ao2+ a1 cos(2π ft) + a2 cos(2π2 ft) + a3 cos(2π 3 ft) + ...
+ b1 sin(2π ft) + b2 sin(2π2 ft) + b3 sin(2π 3 ft) + ...
Spring 2006 – Week 8 PHY 131 14
Spectrum Analyzer
SpectrumAnalyzer
x(t) = ao2+ a1 cos(2π ft) + a2 cos(2π2 ft) + a3 cos(2π 3 ft) + ...
+ b1 sin(2π ft) + b2 sin(2π2 ft) + b3 sin(2π 3 ft) + ...
Spectrumx(t)
Waveform
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Spring 2006 – Week 8 PHY 131 15
Example of Spectrum Analyzer
• LabView Program
• AudactiyFree software to record and edit soundhttp://audacity.sourceforge.net/
http://audacity.sourceforge.net/