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

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rf-loop:

--- Quote from: Mechatrommer on October 28, 2023, 01:19:10 pm ---Turn off sinc, turn on dot mode, calculate how many points and sample rate there is. If you are lucky, and the scope is not transparent enough, you'll be surprised dho800 or low entry siglent can do 10GSps on screen on single channel smallest time div. Where do all those extra points come from? Sampled from actual event? Or simply.. approximated? If your eyes sharp enough, Lecroy sda6000 snapshot i linked earlier did 100GSps.. wow? No!

--- End quote ---

Please, explain this part in bold.
Do you know what you are saying or was it just what you just believe. My opinion is that religion is not for this forum.

I have used and examined many (nearly all) Siglent SDS1000 models including the 1000X HD and all 2000 (2000, 2000X, 2000X Plus, 2000X HD) models... also some 6000 models.
Based on these my experience and knowledge, your statement is not a general truth.
Be it anyone, it would be nice to stay as close to the truth as possible.

rf-loop:

--- Quote from: Fungus on October 28, 2023, 10:17:36 am ---
Turning off sinc is NOT a good idea. Learning to interpret what you see IS.

--- End quote ---

In many cases turning Sinc off (least momentarily and in some cases) is very good idea. But also, sadly, impossible in some oscilloscopes.

But hey, just keep your bullshit generator running, you'll get good numbers in the message counter if you get any pleasure out of it.

mawyatt:

--- Quote from: Mechatrommer on October 28, 2023, 09:47:30 am ---
1) try drawing a square wave on paper, (a realistic signal you can think) with a little bit distortion in 2nd, 3rd etc harmonics... and then think yourself as sampling machine creating sampling dots a little higher rate than fundamental frequency * 2.5 and connecting lines among dots. fundamental will not alias, i think we both agree, you'll see trapeziods or triangles that still can (barely) capture data (if its like digital serial data transmission). now increase a little bit sampling rate just below 2nd harmonics / 2... yes 2nd harmonics will alias, but when you connect the dots, you can still see square waves closer to original signal and if its serial transmission, you can still recover its data content.

2) now on to 2nd, 3rd etc harmonics. if they alias so badly up to a point rendering fundamental (1st harmonics) unrecognizable, then we have problem with signal integrity, reflection, mismatch and all... or analog signal distortion or oscillations so badly, yes we need higher priced DSO. if we dont have money, we can low down our cheap DSO to single channel only at max sampling rate to tackle problematic signal one by one. but since discussion is on a "fairly good" square waves, then imho aliasing will not affect much our judgement (given the bad Sinc interpolation is turned off)

--- End quote ---

Note a proper squarewave has no even harmonics, even a terrible rise/fall time "squarewave" at limit, a triangle wave if you will, has little or no even harmonics (triangle has no even harmonics). A pulse waveform can have even and odd harmonics of varying intensity depending on duty cycle, in the limit of "zero" pulse-width becomes a repetitive "impulse".

We mention this because it seems many folks are a bit confused about this topic.

Best,

Mechatrommer:

--- Quote from: rf-loop on October 28, 2023, 01:38:12 pm ---
--- Quote from: Mechatrommer on October 28, 2023, 01:19:10 pm ---Turn off sinc, turn on dot mode, calculate how many points and sample rate there is. If you are lucky, and the scope is not transparent enough, you'll be surprised dho800 or low entry siglent can do 10GSps on screen on single channel smallest time div. Where do all those extra points come from? Sampled from actual event? Or simply.. approximated? If your eyes sharp enough, Lecroy sda6000 snapshot i linked earlier did 100GSps.. wow? No!

--- End quote ---

Please, explain this part in bold.
Do you know what you are saying or was it just what you just believe. My opinion is that religion is not for this forum.


--- End quote ---
i dont own siglent, i only assume. But please!  Show me gibbs effect in dot mode in siglent scope, a good scope should tell the truth about where its sampled points are located. What religion got to do here? Are you trolIing? empty talk without proof is that..

nctnico:
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. There is a tradeoff to be made by the user.

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