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Topic: IDDATA, ETFE and Frequency Spectrum
Replies: 2   Last Post: Apr 12, 2011 4:51 AM

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Posts: 61
Registered: 11/6/06
IDDATA, ETFE and Frequency Spectrum
Posted: Apr 11, 2011 11:22 AM
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I have been using the IDDATA function on time series data collected at
100hz and using the ETFE function to create bode plots. I would now
like to use frequency data instead of time series when I enter it into
IDDATA, but was wondering if there is a way to tell what IDDATA and
ETFE are doing to the data to convert the time series data to the
frequency spectrum? Is this simply taking the FFT(time_series_output)
and FFT(time_series_input)? I would imagine it is a little bit more
complicated than this?

So I currently do this:
DATA=iddata(time_data_output, time_data_input, 0.01)% where (output,
input, 1/capture rate)
G=etfe(DATA,[],length(time_data));%where [] describes no smoothing,
and NFFT points is the length of time series data

I would like to enter frequency data into IDDATA, and the help says to
use this format:
DAT = IDDATA(Y,U,Ts,'FREQ',Freqs)%where Y and U are now frequency data

However, I was wondering if there was some way to replicate what
IDDATA and ETFE data uses to create the frequency spectrum?

If anyone could help, or refer me elsewhere, I would greatly
appreciate it!

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