setting video bandwidth spectral measurement

[intern_tuv]

Hello, I am a german intern (please do not look on my grammar!) in a US company and my last weeks consisted of playing with arrays, clusters and tab controls to set up a new design for a control panel in LabVIEW. So, I am a real beginner in using LabVIEW.
My next task is to build an individual spectrum analyzer with different functions. Our Hardware: NI 5600 Downconverter, 5620 Digitizer, 5610 Upconverter, 5421 AWG. Software: LabVIEW Full 7.1, Spectral Measurement Toolkit....
I was really impressed to find this great amount of examples for perfoming spectral measurements. And I think I will try to mix a few examples and make later a few changings to get my own analyzer.
My question concerns the following: is it possible to set the sweep time and video bandwidth like with an ordinary spectrum analyzer.
Do I have to create a special vi or is there an earsier way for such individual settings.
Thank you very much for all answers.
Norbert

[Evan R]

Hi Norbert,

Dien Englisch ist zehr gut! Wie ist mein Deutches?

There are examples available on our website of methods to perform frequency sweeps. Essentially, a program must be written in LabVIEW to do this.

Please review the following link:

LabVIEW Frequency Sweep Example for the NI PXI-5404
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B9F1D43AFA2F28B3E034080020E74861&p_node=DZ52285&p_source=External


Good luck with your application!

Best Regards,

Evan R.
Applications Engineer
National Instruments
http://www.ni.com/support

[LV_Pro]

I'm not sure that what you are looking for is valid. In the standard "traditional" spectrum analyzer a narrow bandwidth variable frequency filter is swept across the band of interest, but when you are doing it digitally you basically are getting everything and then using an FFT to resolve, from the complex waveform received, the components that make up that waveform. Usually the only filtering is to limit the maximum frequency to below 1/2 of your sampling frequency to prevent aliasing (Nyquist theorem) Similarly, I'm not sure what in the FFT realm cooresponds to "video bandwidth" on your Agilent or Rhode & Schwarz Spectrum Analyzer. The width of your FFT's bins, which might be coorespondent, is related to the sample rate/sec and the total number of samples (which needs to be a power of 2), i.e. sampling at 11025 samples/sec, analyzing a sample set containing 8196 produces 11025/8196 = 1.35Hz wide bins. Now cooresponding with the sweep time on a SpecA the time needed to collect those samples would be #S* period, or #S*(1/fS) = 8196*(1/11025)= 0.743Sec. The more samples (higher resolution, narrow bin widths) the longer "the sweep".

P.M.

[intern_tuv]

thanks everybody

I think at first I have to speak with my supervisor about the difference between analog and digital spectrum analyzation and than again about the targets in my project.
Hey, but I think I will often refer to this forum in the future, when I have more problems.
And I think there will be a lot of problems