- Read the data from the file into an array, containing complex values. See textread, or the import wizard.
- Call the ifft function. This is general - it does not require any particular symmetries.
iFFT for Band-pass Measurement
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Hi,
I have a outsource data (txt. file)of a band pass measurement which i took from a vector network analyzer. Measurement was made between 700 MHZ-1GHz The data contains 2 columns; 1. 301 measured frequency points 2. real return loss values of points. I have to transform the data from frequency domain to time domain with ifft function in order to calculate distance to fault on a coaxial cable How could i do it? My data is not complex conjugate and not symetric. Shoul i zero padding and mirroring ? What should i do to take ifft?
Thanks in advance!
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Answers (6)
David Young
on 17 Apr 2011
Solve the problem in two stages:
jks
on 2 May 2011
i am working on the same kind of problem , please let me know if you have solved the case
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Joh Yhan
on 9 May 2011
Hi cmd,
Try to replace your fstep to the following. B is the measurement bandwidth.
fstep = B / N;
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AK
on 10 Jan 2012
Well I am also working on some similar kind of problem in 5-10 GHz range which i obtained from VNA which i need to calculate ifft but assuming zero values in 5-10 GHz range will always make results go wrong so some other technique will be required to be done. please let me know if r able to find solution to this answer
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Walter Roberson
on 10 Jan 2012
We *might* be able to find a solution to this, but to do that we need you to answer the questions raised in response to your Question on this topic, http://www.mathworks.com/matlabcentral/answers/25345-ifft-of-bandpass-signal-data
Dr. Seis
on 10 Jan 2012
You cannot reconstruct your timeseries unless you have either:
1. Complex values for both positive and negative frequencies. The real parts of the amplitudes are symmetric about 0 frequency, while the imaginary parts of the amplitudes are anti-symmetric [i.e., imag(G(f)) = -1*imag(G(-f)) ] about 0 frequency.
2. Absolute values for both positive and negative frequencies (which are symmetric about 0 frequency) and the phase-angle information associated with the real and imaginary parts.
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