ifft with a log scale

[dksteel]

I currently am reading in a data file that has the frequencies in a log scale.  I understand that I cannot to a ifft if the frequencies are not in a liner step.  I was wondering if anyone knew how to do a 2-D interpolation to try and space my signal at a linear step.  I was trying to space at 1MHz, below  is some of the data I am reading into labview.  Any advice or help would be greatly appreciated.  Thank you!

David Steele

Frequency (GHz) Voltage (V)

0.22000 0.082643

0.22220 0.16803

0.22442 0.14800

0.22667 0.079847

0.22893 0.071640

0.23122 0.18030

0.23353 0.12486

0.23587 0.25161

0.23823 0.089895

0.24061 0.11021

0.24302 0.15196

0.24545 0.12334

0.24790 0.17741

0.25038 0.29914

0.25288 0.15243

0.25541 0.18977

0.25797 0.15024

0.26055 0.082443

0.26315 0.060924

0.26578 0.044015

[altenbach]

If a simple liner interpolation is sufficient, you could use my example example (Interpolation.llb) posted a long time ago

(Of course you could also get fancy and use e.g. splines)

[dksteel]

I'll give it a shot.  Thank you!

[altenbach]

Here's a quick modification to show one possibility of a linear interpolation. You can increment any way you want. I choose a fixe number of points between the first and last value. (I assume that your real data has more points, with the current limited data set the voltage variation is too steep between adjacent data points and linear interpolation is probably too much of a simplification.)

(LabVIEW 7.1)

[dksteel]

Thanks again for all your help.  I was able to take your earlier example and modify it to get it to work.  I am stepping through the frequencies in the MHz range so I am pretty sure that my ifft resoultion will be very reasonable.  Thanks again for helping!!

Dave