> On 06/06/11 18:40, J. Forster wrote: >> IMO, the lesson is that digital scopes do not always accurately depict >> what a circuit is doing. Even a $50 analog 'scope would never have this >> issue. > > Out of idle curiosity, what sampling mode were you using? (ACQUIRE menu > on my TDS2024B). > > In SAMPLE mode, you're guaranteed to see this kind of aliasing. It's > usually best to run digital scopes (especially the cheaper ones with > limited acquisition RAM) in PEAK DETECT mode.
OK. It was a couple of weeks ago so I can't tell definitively, but probably SAMPLE, with 4 WF average. > What this does is keep the acquisition front-end running at maximum > speed and stores the minimum and maximum values recorded in each 'sample > bin'. You still only have 2500 data points out of the (say) 2.5 million > the scope might have analysed, but the min/max will at least tell you > "there's a signal here" even if the scope doesn't have the memory / > resolution to tell you what that signal *is*. > > If you decide that the burst is interesting enough to look at (and you > know what the repetition rate is), you zoom in (TIME/DIV and H POSITION > controls) as normal. > > I seem to recall someone covering this in a Youtube video. Probably Jeri > Ellsworth (jeriellsworth on Youtube or Twitter) or Dave Jones (EEVBlog). > > > It's a big, nasty beartrap and one that's all too easy to fall into. Yup. That's my point exactly. Best, -John =============== > > > -- > Phil. > li...@philpem.me.uk > http://www.philpem.me.uk/ > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.