Hi

I did the following experiment to check the accuracy of the Spectrum assistant.

Simple VSIN with 1V peak amplitude series-connected to a 100kOhm resistor and done fft of the output after activating the transient noise up to 100kHz to avoid aliasing. Strobeperiod=1/24MHz was added. Sine frequency was chosen as 3*24e6/8192 to obtain a perfect fit of the signal on fft samples. Number of points is 8192. Hanging window selected. Number of signal samples = 1 as per manual.

My calculation of SNR over a 100kHz bandwidth gives: rms of signal = 0.707V, and rms of noise = sqrt(4*kT*R*100k) = 12.87uV. Hence, SNR = 20*log10(0.707/12.87uV) = 94.7 dB

However, the Spectrum Assistant gives around 3 dB better, i.e. 97.2 dB. It also reports signal power 1e-5 dB so 0 dB. We obtain close to this number if we do 1/12.87e-6.

So it appears to me that SNR function takes signal amplitude instead of signal rms. Where is the flaw in my reasoning if any?

Thanks, best regards.