There is, what seems to me, an error with coherent averaging.
I first noticed that with certain sampling rate and FFT length ratios, when coherent averaging is turned on, measured signal and harmonics would start to jump down and up by several dB and up to 10 dB or more in some combinations. As a result, measured distortion would with averaging go down considerably.
However, if option “Show phase of harmonics” is checked, then signal and harmonics remain stable with any sampling rate/FFT length combination and only noise floor goes down reveling low level signals.
I wonder which is correct application behavior, suspecting it to be the latter.
Measuring across distortion range from -120 dBc to -80 dBc, produced 4-6 dB worse results with harmonics phase turned on.
Regards,
Boris
I first noticed that with certain sampling rate and FFT length ratios, when coherent averaging is turned on, measured signal and harmonics would start to jump down and up by several dB and up to 10 dB or more in some combinations. As a result, measured distortion would with averaging go down considerably.
However, if option “Show phase of harmonics” is checked, then signal and harmonics remain stable with any sampling rate/FFT length combination and only noise floor goes down reveling low level signals.
I wonder which is correct application behavior, suspecting it to be the latter.
Measuring across distortion range from -120 dBc to -80 dBc, produced 4-6 dB worse results with harmonics phase turned on.
Regards,
Boris