Spectrum Analyzer with Tracking Generator - do I have what it takes?

[therealkilkenny]

Hi Guys and Gals,

I need to profile the response of some filters in an ultrasonic bit of hardware. I've been told that a Spectrum Analyzer with a Tracking Generator will do what I want in a short space of time, but I don't have one. Problem is I don't know what a spectrum analyzer is (beyond the obvious - analyses the frequency spectrum response).

I have a 100MHz Arbitrary Function Generator under LV control and I have a LeCroy 600MHz Oscilloscope under LV control and I know a bit about writing LV.

The question is, can I use the AFG, the Oscilloscope and LabVIEW to make myself a Spectrum Analyzer to do the job?

Any suggestions or pointers gratefully received.

Dr Phil

[Darin.K]

I believe a Network Analyzer will be of use to you, and fortunately you have the makings of one.  A NA will tell you the amplitude and phase response.  The easiest thing to do is to split the signal from the AFG (use a T) and send one signal straight to the scope and the other to the input of the DUT (device under test).  Connect the DUT output to the second channel of the scope.  Simply measure the ratio of the amplitudes and the relative phase of the two channels and you are all set.  The scope probably has these functions built in, otherwise acquire the time series and let LabVIEW do the work (you can also take the power spectrum if you really want a spectrum analyzer).   If you want to be careful, make sure that the cable lengths in the two paths are equal, but at ultrasonic frequencies I wouldn't worry about it at all.

-Darin

[Tony_G]

Hi Dr Phil,

Some of the LeCroy Scopes have Spectrum Analysis in their Math Functions such as in the WaveSurfer range.  Which one do you have?  If not, bring the waveform in to LabVIEW and then let LabVIEW do the Spectrum Analysis instead (you would need a LabVIEW Full Development or higher).  If the LabVIEW version you have is Full Development v7.0 or higher, then you can use an Express VI called Spectral Measurements.VI, which will get you running quickly.

Best regards,

Tony Gibbs

Applications Engineer

NIUK

[alanjb]

Hello Dr. Phil,

Alan from LeCroy Tech Support here... As mentioned previously, your scope quite likely has the "FFT" math function which performs a spectral analysis of your waveform.   Feel free to contact me if you have any questions.

Best Regards,

Alan