That's an interesting, if unexpected, obsveration.
It's really not unexpected and it is a form of, or at least closely related to, aliasing as mentioned earlier by
gf.
Anyway, that peculiar 'wiggle' is an artefact of the SDG after all!
You may be able to reproduce a similar artifact from an AWG using interpolation to generate square waves or pulses, but that isn't the only cause of an effect like this. There's a couple of differences and ways to tell them apart. I don't get any such artifact from my SDG at exactly 1kHz and I would not expect to. If you do, then perhaps yours is special! However, I do get a similar but discernably different artifact at 1.0001kHz, which I do expect since you can't get that exact frequency by dividing the clock. You can see that the rise time varies, but there are no significant varying 'waves' beyond the transition as there are in my first video.
https://youtu.be/Nr_ySvSPa0UThe difference between this and my first video and the one from
oz2cpu is that here there are plenty--30 or 40 at least--samples that cover the event in question. That is enough so that even if you shift them around, all of the sinx/x interpolations will be virtually identical. The other two only have 3-5 samples for the entire event which is not enough to accurately capture the overbandwidth components of the edge and shifting them around results in significantly different sinx/x interpolations for each capture.
So some of the ways that you can tell the difference between the effect I'm describing and the one you describe are:
1) switch from vector to dot display and use a little persistence if you need to--your effect will remain, mine will not
2) consider the number of samples and the BW/rise time of the various instruments. In the YT video
oz2cpu posted there are 4 samples per division and IMO the varying sine wiggles reflect that, not any actual signal.
3) use a non-DDS source like I did in my first video to see how the scope can perform with a known consistent fast edge.
4) look and see if the rise time alone is shifting or if the whole thing is wiggling like a snake or at higher wfm/s, showing a wide trace at and around the tops and bottoms of the rising edge. The latter is due to the effect I describe.
oz2cpu can rest assured that his SDS2000X+ isn't the culprit after all in this case.
Well obviously I completely disagree and I've shown the video previously of the same effect where it clearly isn't the source. My fast edge is much, much faster than the scope, so there's no doubt that the effect is all scope. In
oz2cpu's video, I suppose it is less clear since the AWG and scope rise times are in the same ballpark
if the scope has been upgraded and is not the original 200MHz. But as I observed earlier, I wouldn't expect any Easy Pulse interpolation at 1kHz. If the scope has been upgraded to 500MHz+, then perhaps some of the effect could be AWG interpolation at the frequencies that don't divide evenly.