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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Bonjour,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I have measured the phase and magnitude response of a system and I am
trying to identify a model for it with frfit(). This works well up to about
10Hz but then can be 20dB different in gain, 150degrees in phase. Best fit is
with order 3 or 4.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>My data is a log frequency sweep from 0.7Hz to 60Hz. It is a little
noisy (+/- 0.5dB, +/-3deg). The response has a ‘peak’ in the phase
between 7 and 20Hz and increasing gain over this region.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I tried separating the model. First I divided the measured data by the
modeled response (to extract just the data that does not fit the model) and
then frfit() to the remaining data. This did not help as the fit to the
remaining data was just as bad.</span><o:p></o:p></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Can anybody suggest how to analyse this system?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Thanks for any help,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Regards, John<o:p></o:p></span></font></p>
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