Hi. In the manual of the qa402 I have not found the definition of the measures that can be carried out (at least I have not found them), while in the manual of the qa401 (from page 33) there are. I noticed that among the measurements that can be done with the qa402 there is also N - D, but I have not found the definition. In the qa401 manual I found the definition of the N + D measure. Do the two measures have the same definition or are they 2 different measures? Thank you

Hi @Claudio, the definitive source for the definition of measurements is at the Analog Devices link below. That can help untangle SNR, THD, THDN, etc.

The N-D, as you point out, is potentially confusing as that terminology isn’t used elsewhere directly. In a SINAD measurement, the numerator is signal, and the denominator is “noise and distortion”. Usually, if you are talking about a noise measurement, the noise is “without distortion”, which is why SINAD references noise AND distortion. So, when you see SNR, the denominator is noise only (no harmonics).

SINAD compares the carrier to N+D, and SNR compares the carrier to N-D

So, the N-D is just the noise minus the distortion, which is, conventionally, just noise. There probably should also be a N+D measurement to make things a bit more orthogonal.

I think there’s a work item to add a tooltip so that you see more info on the measurement when you hover over it in the picker dialog.

it’s a good idea. Thanks Matt