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njit-etd2003-081 - New Jersey Institute of Technology

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98<br />

technique is measurement time. The transfer function is estimated over a user defined<br />

frequency range at a single frequency point at a time.<br />

In measurement situations where there is reasonable linearity and good signal to<br />

noise ratio, the broad-band FFT based network analyzer provides the transfer function<br />

estimate in a fraction <strong>of</strong> the time that is normally needed by the swept sine approach.<br />

The excitation is usually a periodic chirp or bandlimited random signal, but the<br />

adventuresome user has full control over the excitation including user defined (arbitrary)<br />

excitation.<br />

Figure 3.14 Optimal data acquisition measurement system.<br />

In the end, the amount <strong>of</strong> time required for a transfer function estimate is set by<br />

five factors:<br />

1) the system's noise<br />

2) the system's linearity<br />

3) the number <strong>of</strong> frequency points in the estimate<br />

4) the accuracy required<br />

5) the time for basic data acquisition

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