Need help with FFT function
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Need help with FFT function
I am using MathCAD for the first time today, and have a problem that requires your assistance. I have to create a waveshape, and I do so, but the points are separated by 1 unit, not the 1 microsecond units that are the reality. For this reason, I have no idea what the output of the FFT X axis is. I've given it no frequency reference, so is it using 1 Hz as the basis for the difference between each point I've entered (not the truth). I'd like to know how to get this software to accept 1 microsecond as the difference between each point that I enter. I also need to know how to interpret the output of the FFT.
The spreadsheet is here:
Re: How do I change the graph in the attached file... - PTC Community
There are various example mathCAD sheets attached. I've tried various things, but can't get them to work.
Thanks.
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Electrical_Engineering
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All show same dft results. Their fundamental spectrum is same. But the frequency is f.
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An FFT of a vector of observations has no frequency information; it only uses the number of values in the vector. To assign a frequency you must define the "sampling frequency", or the time interval between the values in the vector..
Attached is a sample sheet done as I transitioned from real Mathcad to Prime Express. It explains the concept of sampling frequency, then moves on to a whole lot of things you may not care about.
Don't forget--the FFT can only tell the truth at frequencies below half of the sampling frequency (Nyquist frequency), so you need to be sampling pretty fast!
File is Prime 4.0 Express.
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Okay, I knew the Nyquist frequency existed.. So, if I sample at a 1 microsecond interval, my sampling frequency is 1 megaHertz, and the x axis of the MathCAD plot needs to be read in terms of megaHertz. In other words, the 1 on the output plot is 1 Megahertz? It plots up to 500 Mhz due to Nyquist limit?
Thank you, sir.
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Sorry that should be up to half a Megahertz as the max frequency. 500 kHz.
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This is your 500 kHz spectra 200 and 201 row. Plot it by green line.
