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Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)
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Mechatrommer:

--- Quote from: nctnico on October 28, 2023, 02:06:09 pm ---In dot / vector mode, you won't get the Gibbs effect because it comes with sin x /x reconstruction. Still, the sin x/x reconstructed signal is the closest you'll get to seeing something that resembles the real signal when you are getting near the nyquist limit....

--- End quote ---
no... see above...
gf:

--- Quote from: Mechatrommer on October 28, 2023, 05:52:38 pm ---Gibbs effect succesfully produced in (sinc_on.jpg), but when in dot mode (dot_on_run.jpg or dot_on_stop.jpg) Gibbs dissappear, if you try imaginatively (if you dont want to try it on paper) to connect straight line between point to point in dot mode, you wont see any Gibbs effect. Gibbs only appear when Sinc interpolator is turned on in scope. do you understand what i meant before posting?

--- End quote ---

I guess that your signal is undersampled. Then It is expected to happen. Consider it an aliasing artifact. A properly bandwidth-limited signal is reconstructed almost exactly by sinc reconstruction, but if the signal fed into the ADC violates the sampling theorem, then perfect reconstruction from the samples fails and the reconstructed signal looks different from the original signal you fed into the ADC.
gf:

--- Quote from: Fungus on October 28, 2023, 02:27:15 am ---To me that looks exactly like a bandwidth limited square wave:
...
Nothing to do with sinc function.

--- End quote ---

The relation is the inverse Fourier transform of the frequency response of a linear phase brickwall filter. It is a sinc function in the time domain. IOW, applying such a brickwall lowpass filter in the frequency domain is equivalent to a convolution with a sinc function in the time domain.
Fungus:
turn off Sinc...
[/quote]

You can turn off sinc on a DS1054Z when there's 4 channels enabled but it replaces it with a different filter. You're not seeing raw data.
2N3055:

--- Quote from: Mechatrommer on October 28, 2023, 05:52:38 pm ---here i tried to replicate 2N3055's capture of Gibbs Effect in my DS1054Z. i dont have fast rise time 16MHz that can produce 10mVpp, but since the focus is on Gibbs Effect (whether its real or not?), the closest i can get is Leo Bodnar's pulse 10MHz @ 1Vpp. and then i figured i was actually struggling to get as low sampling rate i can get similar to 2N3055, i have to turn all channels ON and have to go up to 2us/div, reduce memory depth down to minimum 3Kpts/ch, then only i get 125MSps, but at this time/div, the cycles are too densed together to give any useful info for the purpose. so i have to dial back down 20ns/div and thats at 250MSps, thats the closest i can get. we cant set sampling rate to our heart content in Rigol, apart from reducing mem depth and increase time/div... other than that its automatic, maybe to avoid nasty Gibbs? who know?

turn on Sinc, vector plot (sinc_on.jpg)
turn off Sinc, dot mode (while running/capturing) (dot_on_run.jpg)
turn off Sinc, dot mode (Stopped to better see points) (dot_on_stop.jpg)
turn off Sinc, vector plot (sinc_off.jpg)

Gibbs effect succesfully produced in (sinc_on.jpg), but when in dot mode (dot_on_run.jpg or dot_on_stop.jpg) Gibbs dissappear, if you try imaginatively (if you dont want to try it on paper) to connect straight line between point to point in dot mode, you wont see any Gibbs effect. Gibbs only appear when Sinc interpolator is turned on in scope. do you understand what i meant before posting?

so tell me Mr sharp trained eyes Fungus (and others who have sharp eyes or brain) which signal do you like? or think its true happening on circuit?.. sinc_on.jpg? sinc_off.jpg? or dot_on_stop.jpg? or all true? because when i turn on Sinc, suddenly something on front end DSO pcb clicked and activate 8th order non-causal Chebysev?

and can any S or other brand DSO to do this test? and demonstrate here? cheers..

--- End quote ---

I repeatedly politely asked you to stop using my images and FALSELY claim what I said they mean and ascribe to them completely wrong conclusions you are spewing.

I explained what they are, how they were made and what they mean.

Your weird explanations are just that. Weird.

You have some grasp about math theory behind and some grasp of how sampling and DSO internals works. Just enough to arrogantly think you know it all. Better than all of the rest of us, including, among others, PhD who designed ADC for living, some people that designed scopes, and other very good engineers.....

Stop doing it and listen to explanation why are you wrong. You are behaving like flat earth people. There is no conspiracy, not everybody except you are stupid. It is simple. You are wrong.

Gf very nicely, eloquently and very concisely said what is going on.

That being said.
You seem to be confused by dot mode.
You are correct that dot mode can (in some cases) better show signal shape when signal is partially undersampled.

Do you understand why?

As an example I can show 10 MHz square wave signal, sampled at very low 25MS/s in dot mode. Signal is band limited with 200 MHz filter, so there are no frequencies (odd harmonics up to 19th in this case) above that. Simple edge trigger. Scope is my Siglent SDS6000.
Reference image is same signal, just sampled at 5GS/s.

Signal sampled with 25MS/s is perfectly reconstructed.
Can you explain why?

Let's start with that. Then we will proceed from there. Explain that first.
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