low frequency reslution

[sky1981]

Hi,

I am using labview to get the frequency spectrum of different waveforms, Has anybody got an idea how shall I increase the frequency reslution of a waveform because I have 6 different waveforms simillar to each other and I need to differentiate between them. so what shall i do to increase the reslution?

[Coq_Rouge]

The frequency interval is given by the following equation:

df=Fsample/n
where n is the number of samples in the sequence.

So you can increase your sample rate and/or the number of samples analyzed. Have you tried a Hanning window?

[cebailey]

If you are using Fourier transforms you should consider that the transformed dataset will have an amplitude measurement for exactly one cycle per the duration of your original dataset, and for exactly two cicles per your dataset, and three, and other integer values up to half the number of measurements you took.

There will be no information about any frequency that does not correspond to an integer number of cycles in your dataset.

[MattBradley]

Your minimum sampling rate should be 2.56 x the maximum frequency you expect.  Sampling at Nyquist (2x) will only preserve frequency info, not amplitude info.  Generally, I like to sample about 10x if possible and for as long as possible.