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3224: Best metod for low noise, low frequency spectrum mes?

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3224: Best metod for low noise, low frequency spectrum mes?

Postby Wavelength » Wed Apr 09, 2008 3:49 pm


I need to test the noise on power supplies for clock oscillators. The typical method is to use a spectrum analyzer at the lowest frequency base with AC inputs and get a spectrum of the noise using average and log X axis.

The problem with R5 is that while you can do this and for low frequencies (0-73Hz) the problem is the software does not show anything below -110dB.

With a 12 bit signal analyzer like the HP 356X series they usually go to -130dB and -150dB for 14 bit.

I tried using the ADC-216 which does allow up to -150dB on R5 but it has it's own set of problems.

With the 3224 and R5 I can first do a shorted probe measurement to get a baseline for noise. Then merge that with the UUT and get a better result. Unless the noise floor is below -110 for which then it just dies.

Another problem which I noticed yesterday is that everytime the R5 software does an average it opens a new window. I could not understand why R5 kept crashing until I realized this. I expected it to keep averaging over the same window.

Anyways... I am trying to get some pretty low measurements as I have some new discrete regulators in the 33nV-100nV range. So if anyone can tell me how to use the 3224 to accomplish better testing I would appreciate it.

J. Gordon Rankin
Wavelength Audio
Posts: 4
Joined: Tue Apr 01, 2008 4:09 pm

Postby picojohn » Tue Apr 15, 2008 9:04 am

Hello Gordon,

To achieve a merge using PS6 would require that you export the data in spreadsheet format and perform the manipulation there.

Saving a spectrum view as a .csv file is problematic with the current version of PS6, but will be resolved in the next release.

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I hope that this is helpful.

Zen Master
Zen Master
Posts: 382
Joined: Mon Jun 11, 2007 1:10 pm

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