Hi TomC ++,
so here my pics:
#1 : That's how it started, just the SDS9302 at 2mV/Div and the Tek SG505 with output on.
#2 : Same but just screen shot.
#3 : As #1 but SG505 output switched off.
#4 : As above but just screen shot.
#5 : Just Tek SG505 and 475A (at max sensitivity - 5mV/Div) together.
#6 : As above, 475A screen shot only.
#7 : Tek SG505 and 475A with SDS9302 not shielded.
#8 : As above 475A screen shot.
#9 : As above SDS9302 screen shot.
#10 : Modified oil can.
#11 : Owon put into oil can - 475A screen shot.
#12 : As above - display detail version 1.
#13 : As above - display detail version 2.
#14 : As above but SG505 output Switched off.
Screen shots of the caged SDS9302 I will do after I cut a window in my oil can. And I think about some kind of metal grid to cover the window which then I can put on and off.
Perhaps I have one of this very fine meshes Tek offered as an option back then but have to search my stock - don't know yet...
The detail pics (#12+13) show very little residual noise on the peak of the sine waves after the Owon had to go into the can and the last pic also shows what's left of the spikes you can clearly see on both displays as long the Owon is 'free' (#7+8+9).
Last thing to add: The Tek 475A connected to the Owon 'swallows' a certain amount of Owons emissioned noise due to its solid mass some how (another effect for you to think about - I have no absolute clear picture yet because where does it go then? Perhaps is it just spread out more widely?). So for the moment its just the reduction achieved by caging the Owon that I can show (pics #7...9 versus #11...14).
So hope all pics are OK so far (turned 475A's intensity up to make anything in the backgroud visible but that also blurres the trace a bit).