how to find the ratio of two frequencies in fft

[johnsasikennedy@gmil.com]

Hi i am john,

I need to find the ratio of 1st and 2nd frequencies in fft graph.

Already i got information from this site only. Mr. Alten helped me.

Now i have to continue the same problem and need to find the ratio of the frequencies.

Please someone help me guys....

I will attach my vi file and text file.

[johnsold · Accepted solution]

john,

Do you need the ratio of the frequencies or the ratio of the amplitudes of the components at those frequencies?

The Extract Multiple Tone Information.vi from the Signal Processing >> Waveform Measurements palette should do what you want.

The frequency resolution is not very good because you have relatively few cycles of the waveforms (~2 for the lower frequency). I added some zero padding to improve the resolution, although a larger data sample would be better.

Lynn

[johnsasikennedy@gmil.com]

Thanks a lot  Mr.JohnSold. 

But i need to find fft for the other sample of datas. i cant be able to get it through the vi which u have posted. please check it and send me the new program. Sorry for disturbing u. 

PFA

[RavensFan]

Why can't you use the same VI on a different set of data?

Why did you post the exact same response to your other, very similar message trhead about FFT.?

http://forums.ni.com/t5/LabVIEW/How-to-get-fft-for-my-xy-graph/m-p/2685637#U2685637

Don't create a new thread for the same question.  Keep your responses in the other thread.

(PS.  There is no word spelled "u".  There is, however, a word that is spelled "you".)

[johnsasikennedy@gmil.com]

sorry. But i need it urgent. Please do the needfull

[johnsold]

The negative times in the two files you posted may be part of the problem. Shift the time axis so that all the data occurs at non-negative times and see if that helps.

Lynn

[johnsasikennedy@gmil.com]

Its not coming properly. Will you be able to help with the program

[altenbach]

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johnsasikennedy@gmil.com wrote:

Its not coming properly. Will you be able to help with the program

---

Look at my reply in the other parallel thread.

The negative times are not a problem, because we only care about dx in the resampled data. You simply need to ensure to trim the leading zeroes due to the non-numeric file header. (or edit it out manually from the file).

(Also please don't use these doule-extension. *.lvm.txt. That only confuses!)