Power Spectrum.vi changes in LabView 2012?

[cochenob]

Call me crazy....but....

If I open up ANY of the shipped USRP examples dealing with receiving...just about all of them use "FFT Power Spectrum.vi".  This returns a 2-sided power spectrum centered at the carrier (going from -Fsamp/2 to +Fsamp/2)

I can't find this same VI in LabView 2012.  I DO find a similar VI called "FFT Power Spectrum and PSD" under the Signal Processing collection....however this VI returns the spectrum with the carrier at 0 (going from 0 to +Fsamp).

If I try and copy the "FFT Power Spectrum.vi" from the shipped examples into a new blank VI in LV 2012...it appears to automatically revert to the 'newer' "FFT Power Spectrum and PSD".

It seems as if the Power Spectrum VI got 'updated' in LV 2012?  The old one (centered spectrum) still works so long as the VI you wrote it in is pre-2012.

Can anyone confirm this?  I sort of enjoyed (and preferred!) the centered spectrum.  Was intuitive to interpret.  Looks like I need to either recalibrate my brain or try and re-center things on my own after calculation.

---

Brandon

[cade]

Hi Brandon,

I just want to clarify which VI you were using in the earlier version of LabVIEW. Were you using "FFT Power Spectrum.vi" or "Power Spectrum.vi"? If using the later, then the VI still exists in LabVIEW 2012 as shown in the help document linked below.

Power Spectrum VI:

http://zone.ni.com/reference/en-XX/help/371361J-01/lvanls/power_spectrum_sxx/

Thnaks,

[cade]

Hi Brandon,

I just want to clarify which VI you were using in the earlier version of LabVIEW. Were you using "FFT Power Spectrum.vi" or "Power Spectrum.vi"? If using the later, then the VI still exists in LabVIEW 2012 as shown in the help document linked below.

Power Spectrum VI:

http://zone.ni.com/reference/en-XX/help/371361J-01/lvanls/power_spectrum_sxx/

Thnaks,

[cochenob]

If you look at the label in any of the shipped USRP Rx programs...the vi is indeed, "FFT Power Spectrum.vi".  If you dig down far enough into that VI...you will eventually come to the "Power Spectrum.vi" that you mention.  So...the "FFT Power Spectrum.vi" basically takes the more simple "Power Spectrum.vi" and wraps it up with a bunch of different features (averaging, unit conversions, etc.).

Perhaps the best solution is just to take the simplier "Power Spectrum.vi"...copy over the code that does the spectrum centering...and save it as my own special VI.  I tended not to use all of the averaging and unit conversion features anyway.

[Anthony_F]

---

@cochenob wrote:

It seems as if the Power Spectrum VI got 'updated' in LV 2012?  ...

Can anyone confirm this? 

Brandon

---

Hey Brandon,

You are indeed correct that at some point those LabVIEW functions were combined into a single VI. I don't have the specific dates or info aside from the fact they "have identical API and similar functionality."

If I understand you correctly, the older Power spectrum VI doesn't center the graph at 0Hz, it displays it at whatever carrier frequency you are at? If so, you should be able to change the f0 appropriately to have the scaling like it was before.