What else can we do to manifest that this is a bug ?
One key aspect seems to be the definition of a "point".
The range of “dx”in the d/dtmenu is2~20. The measurement unitsarepointand thecorresponding time difference range is 0.02~0.20div. “div” indicates the number of the pixel points that each division has and is 100 for the SDS2000X Plus. If dx = 10 points, the time difference is 0.01*10 = 0.1div Then the differential operator calculates the average slope in10 points of the selected sourceand dx represents the time difference between the 10 sampled points.
On the one hand it talks about
pixel points, on the other hand it talks about
sampled points (which I would associate with samples). So what is really a "point"
At 1us/div, 4 "pixel points" were 40ns, and at 2us/div, 4 "pixel points" were 80ns (according to the definition in the handbook: 1 div = 100 pixel points).
But that's not what we see. The spectrum with the two big lobes tells us that the actual dx was 2ns, at all timebases >= 50ns/div. And 2ns are 4 samples @2GSa/s.
So the implementation obviously assumes that dx is
in samples, and the stuff in the handbook regarding div and pixel points seems to be wrong an just leads to confusion.
Nevertheless, "number of samples" is still an incomplete time specification if the sample rate of these samples is not specifed as well.
For your experiments at > 50ns/div, the scope obviously assumed the raw sample rate of 2GSa/s, even if the d/dt operator is applied to interpolated samples @40GSa/s.
While this could be considered correct, if it were unambiguously documented, I still find it a significant limitation, since It hiders you to do what I intended to do.
[ Similiar to a camera in "auto" mode, which does whatever it thinks -- just not what the photographer wants it to do
]
For <= 20ns things still need more investigation. Could you please capture a single shot of say 4,000,000 raw samples (@2GSa/s) of this signal (I guess 200µs/div gives you that many points?), save them to an ASCII file, and post a link to the file? I would like to get a feeling for what can be extracted from these data, and what to expect.