NI-4461+Signal Analysis

Hi,
We have a NI-4461 Dynamic Signal Analysis card.I need to plot a Freq Spectrum & Bode Plot(Gain Vs Freq & phase Vs Freq).I am able to acquire data using DAQmx functions,but the DAQmx library does not support Signal  Analysis functions such as FFT,gain and phase plotting.I would like to know if a DSA library is available for this card and how do I download it and use it with the card?
Thanks in Advance
G.Bhaskar

Hi Bhaskar,
There's a difference between studying a signal's frequency response and a signals frequency spectrum. For example if you are interested in the response of Vo/Vi as the frequency changes, you would use a Bode plot. A Bode plot is the amplitude vs. frequency or the phase vs. frequency. Usually frequency is logarithmically scaled and the two plots are stacked so you can see their relationship to each other. Phase will change with frequency as well as the amplitude. This is useful in studying transfer functions and how circuits respond to different stimuli.
If you are interested in the spectrum of frequencies that are contained in a signal, you would use an FFT. The highest amplitude would correlate to the fundamental frequency of your signal. This is not the same as phase. If you take an FFT, you will be specifying the frequency resolution (which may not be apparent but your parameters and array length, amongst other things, will set your resolution). So if you're resolution is 10Hz and you're FFT(Vo) = [.2, .2, 51, .2, .4, .3], your fundamental frequency would be 30Hz. Any other peaks above the noise floor will represent harmonics or other tones in your signal. A musical chord, for example, could contain 3 tones but many harmonics.
Please take a look at these documents
The Fundamentals of FFT-Based Signal Analysis and Measurement in LabVIEW and LabWindows/CVI
http://zone.ni.com/devzone/cda/tut/p/id/4278
An Overview of Frequency-Domain Measurements
http://zone.ni.com/devzone/cda/tut/p/id/3011
PBear
NI RF

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