the demodulation method - how to know

[mikhaylova_anna]

Hello,

I have a general question, not about the code itself.

I measure a signal with a sample rate (now it doesn't matter, which one exactly). I have got a series of numbers, which is my signal in the exact time points. Then I use Extract Single Tone Information.vi  and can get the amplitude of my signal (and frequency, and phase). If the sample rate is matched with signal frequency, I expect to get the right result. It's the procedure.

I can suppose for sure, that Extract Single Tone Information.vi implements the demodulation.

The question - what demodulation method does it use? I can assume, of course, but how to know it exactly. I mean, if I can get some results and somebody asks me, how they have been got, I can't say something like "I don't know, it is just system shows it." (it is important to me, because we use DAQ board in scientific area)

I don't need the code of this vi (I don't neeed, of course, the commercial secrets), but can I know the ideas and methods?

Thank you in advance.

Anna

[johnsold]

Anna,

You have asked an important question, one which too often is not asked.

The first place to look for information is the help files. For many VIs the detailed help describes the algorithm used. Unfortunately, the Extract Single Tone Information.vi help file does not have this information.

Next, open the diagram and look at the code. In most of the VIs provided with LV by NI, the code is not secret. If you do this you will find that the VI uses a Hanning Window and a standard FFT, both of which have formulas or algorithms listed in the help.

These are not demodulation functions although you can get some information about modulation types from the spectrum. The Single Tone VI will not give any modulation information because it is designed to look at only one frequency. If you need to analyze a modulated signal, other tools than the Single Tone VI will need to be used.

Lynn