SNR graph in log scale

[Sharmi]

Hi,

I am working on a project with PXI 5663 and PXI 5673 where I have a complex base-band signal and I want to measure the SNR of the signal. I searched in NI discussion forums and found I could use the SINAD vi. I used it but I wan to plot the results with the Y-axis in dB scale and the X-axis in log frequency scale (like the axes for Bode plot).

Could someone please tell me if there is a vi I could use to do it or how can I scale the axes in graph properties?

thanks so much,
Sharmi

[A_Donfigulation_Error_Has]

Hi Sharmi,

Right-click on the Waveform Graph on the  front panel. Go to X-Scale>>Mapping>>Logarithmic. How did you make the calculation using the Sinad VI? Are you referring to the SINAD Analyzer.vi? Have you tried to scale the Y values yourself using math functions or the Formula Node structure?

Regards,

Jason L.

[Sharmi]

Yes I have used the SINAD analyzer vi. I have not tried math function or formula node since I am not sure how to do that.

Thanks,

Sharmi

[A_Donfigulation_Error_Has]

Hi Sharmi,

Page 6 of this http://www.analog.com/static/imported-files/tutorials/MT-003.pdf explains the relationship between SNR, SINAD, and THD. You can make the conversions yourself from linear to logarithmic and then compute SNR by following the formulas. One way to do this is with the Math Function. Information on how to use the Formula Node can be found here: http://www.ni.com/white-paper/7572/en, otherwise use the math functions found on Programming>>Numeric, etc. I don't believe there is anything already pre-built for this.

Regards,

Jason L