Products > Test Equipment
Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)
TimFox:
"Non causal" usually means that the output can chang before (in time) the input does: not realizable in the time domain.
https://en.wikipedia.org/wiki/Causal_filter
A causal filter's output depends only on past and present inputs, not future values of the input.
Digital filters operating on a data set can be non-causal.
Mechatrommer:
--- Quote from: Fungus on October 26, 2023, 10:39:12 pm ---sinc isn't the problem, lack of bandwidth is.
--- End quote ---
so then my 230MHz "DHO924" is in better hand than your 100MHz "DHO814" ;D
--- Quote from: Fungus on October 26, 2023, 10:39:12 pm ---PS: There won't be a way to turn it off. It would be a disaster to just draw lines between the dots.
--- End quote ---
thats too bad. DS1000Z can be switched off. this is useful to visualize and verify (qualitative) what we are seeing is true or possibly a false interpolation. what kind of disaster if we turn it off? at worst we see aliasing. or apparent low BW signal.. interpolation is meant to attempt reconstruct accurate representation, but its proven its not. you are on the side that think the "non-causal"/precursor/gibbs ear ringing is for real do you? |O i'm on the side with R&S and Lecroy ;) are you saying directly download raw sampled data and plot point to point in PC is a disaster? i've had fair amount of time doing that, apart from sharp edges/triangulated plot instead of nice curvy interpolated plot, there is nothing to be afraid of, brain can certainly make better judgement ;)
EEVblog:
--- Quote from: ebastler on October 26, 2023, 07:44:02 pm ---Two things are important here, in my view:
(a) It's not the case that the ringing is actually present on the Bodnar pulser's output and the DHO800 somehow "glosses it over" while Siglent shows the truth. Tautech had claimed that early in the discussion a few weeks ago, but dropped that claim later.
--- End quote ---
I showed in my review video two R&S scope responses, MXO4 and RTB2000 and both of them matched the DHO800. The Siglent was indeed the outlier.
The MXO4 is a 1.5GHz bandwith scope, so it should show everything on the Leo Bodnar generator warts and all, yet there is nothing there.
The Siglent clearly has the problem.
I can do more scopes if needed, but if I'm going to trust any scope in my lab it's the MXO44.
Mechatrommer:
--- Quote from: EEVblog on October 26, 2023, 11:16:20 pm ---The Siglent was indeed the outlier.
--- End quote ---
its clear to me now so far, the problem is imperfect sinc reconstruction. on both siglent and rigol if condition is met. so the argument if this scope is more accurate representation than the others is moot.
Mechatrommer:
--- Quote from: Fungus on October 26, 2023, 11:39:50 pm ---Try it with a single channel and 1.25GSa/sec. It should look the same as my 200Mhz DHO804 if you do that. :)
--- End quote ---
can we upgrade to DHO824 meh? i read its impossible, there is no BT7TO20 option, or did i get outdated? btw i saw your leo pulse when hacking to DHO924, its the same with me now (extra overshoot) but last time i read you downgraded to 100MHz DHO814 right?
--- Quote from: Fungus on October 26, 2023, 11:39:50 pm ---Nope, you've set up a pathological case there and you know it. What you're seeing there is aliasing.
--- End quote ---
aliasing on fast risetime square 10MHz pulse? i suspect you are confused right now. or am i misinterpreting?
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