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1-Newbie

## Problems of Fast Fourier Transform (FFT)

Hello Mathcad community!

I'm unexpirienced Mathcad user, but I was able to solve all my problems and misunderstandings by myself. Till now.

I'm trying to analyse the experiment results of electric field measurement. I wanna convert the result into frequency domain by using Fast Fourier Transform (FFT).

I had done some programming in Mathcad prime succesfully, but now I can't find where my mistake is.

I'm attaching sheet and imgs.

Thank you for any kind of help.

PS.: I'm using Mathcad Prime 3.0

5 REPLIES 5
19-Tanzanite
(To:ptc-5918021)

Please post the data.

1-Newbie
(To:ptc-5918021)

Sorry for missing data files.

19-Tanzanite
(To:ptc-5918021)

The variable on the x-axis, frequency, is not defined.

Edit. I fixed your units issues: d1 should have units of 1/s

1-Newbie
(To:RichardJ)

Thank you for your reply.

I tried to add the unit to all variables. And also define the frequency (f), but the FFT is still not working.

I wanna display the x-axis in frequency domain, the frequency is limited from 0-4GHz..

19-Tanzanite
(To:ptc-5918021)

A few points:

The second half of the vector returned by CFFT is redundant, because it's the complex conjugate of the first half. So you actually only have 2048 points.

Assuming the time spacing of your data represents the actual sampling interval your upper frequency limit is 10GHz, not 4GHz. The Nyquist limit is 1/(2*delta_t).

You can't plot a range variable against a vector. They are two very different things. You need a vector of frequencies.

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