Thank you JBG for your answer.
Indeed it must have been some crosstalk or crossmodulation between channels or external modulation of a special kind.
If I set both channels to square wawe this triple curling appears in both channels!
(you can set your player to continuously replaying this short clip, so you can better see what is going on)
If I push Single on scope, there are always just thin lines (yellow and blue ones), but always they have another shape.
Photos in next post.
That was a more informative video clip. I tried setting VLC to play those 1 second clips on a continuous loop but the best I could do was to get it to play two passes at a time. I had more luck with this 3 second video and the trick appears to be to set the B point a few frames short of the bitter end to achieve continuous loop play. I guess the brevity of those 1 second clips was the reason for my limited success with loop play.
It's surprising what a difference reducing the resolution from full HD down to a 1280x720 clip does for the playing time you can get out of a 4.5MB clip. I'd expect just mounting the camera onto a tripod, locked off to eliminate any camera wobbles would let you get more time for a given file size.
All the common video formats use lossy compression to minimise storage requirements (and reduce writing speed to the media), so the less changes, frame to frame, that have to be recorded, the less the amount of picture data that has to be sent in each group of pictures (GoP), typically half to one second's worth of frames between a total refresh of each key frame during which only frame to frame differences are recorded.
"Wobbly-cam" recordings aren't much of an issue when you're hosting your home movies on Youtube but when it comes to trying to cram a few second's worth of video into a 4 or 5 MB attachment limit, this sort of care in the camera work becomes rather more critical. If you don't have a tripod, you can arrange some sort of stable support to rest the camera upon (a stack of hardback books for height adjustment on a chair or small table for example).
Anyway, having noted those points regarding video technique, I can comment on the effect of this "Magic Pulse" you'd managed to capture. The "Magic" has obviously eliminated the gross 4ns jumps you'd otherwise be seeing with a 6600 or 6800 function generator, lending the movement a more liquid, if ripply, appearance.
It looks like the 'jumps' in phase are now around the 1.5ns mark. The tripling up looks like it could be the effect of the 'scope using some sort of persistence (a one second persistence setting perhaps?), otherwise I'd expect this tripling up effect to produce a blurred image rather than the crystal sharp images of seemingly three horizontal scans worth overlaid on top of each other.
It's quite obvious that you're terminating the 'scope end of those BNC cables with 50 ohms (5Vpp settings with the scope showing circa 2.5Vpp values) so we can't blame badly matched cables for any of these effects. It would be interesting to see whether others in your priviledged position of FY6900 ownership would see the same effect using a different make and/or model of DSO like a Siglent SDS1202X-E for example
Anyway, that's something to ponder on and I thank you for your contribution, both for this longer clip
and for reminding me about the forgotten loop playback option in VLC.
JBG
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