Disc_07 Measuring Freq Response

Disc_07 Measuring Freq Response - 1 Measuring the Frequency...

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1 Measuring the Frequency Response of a System Given some box containing an unknown system we wish to measure its frequency response in the lab. Note that by wishing to do this we are assuming that it is linear, time-invariant; otherwise the idea of frequency response doesn&t exist. How do we do this? Well, remember that we know that H ( ω ) causes a multiplicative change in the input sinusoid&s amplitude and an additive change in the input sinusoid&s phase. Thus, if for a bunch of sinusoids at different frequencies we could measure: 1. the ratio of output amplitude to input amplitude 2. the phase shift between output and input ±then we could get a rough plot of | H ( ω )| vs. ω and H ( ω ) vs. ω . The setup would look like this: System Under Test Sinewave Generator Dual-Channel Oscilloscope Ch. #1 Ch. #2 You would measure the output amplitude, the input amplitude, and the difference in time between the zero-crossings of the two sinusoids; then you would convert the time difference into a phase shift for the
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Disc_07 Measuring Freq Response - 1 Measuring the Frequency...

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