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

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Mechatrommer:

--- Quote from: Fungus on October 28, 2023, 10:03:34 pm ---
--- Quote from: Mechatrommer on October 28, 2023, 10:00:58 pm ---
--- Quote from: Fungus on October 28, 2023, 09:58:08 pm ---
--- Quote from: Mechatrommer on October 28, 2023, 09:32:28 pm ---good! thats "more accurate"

--- End quote ---
This still needs explaining though:
[img]

--- End quote ---
thats where turning Sinc off, or plot in dot mode

--- End quote ---
That is in dot mode...
(according to tautech)

--- End quote ---
then that probably causal... a real signal. who knows whats inside semiconductors IC? that one is not as fancy as other examples presented before. someone mentioned high order "physical/analog/real" filter that can cause apparently non-causal ringing, but i have not be presented with one real life example, and i dont know if the scope has it. or what it does internally in DSP. probing with other scopes, compare and peer reviews may help.

Mechatrommer:
here talking about improperly designed scope? 6GHz BW SDA6000 @ 10GSps, what? (bought used probably phased out from company and out of cal) ;D feel free to pick which one to believe, i would say... close enough... if you still got concerned, really you need more BW and sample rate, and a new one! ^-^

tautech:

--- Quote from: Fungus on October 28, 2023, 10:03:34 pm ---
--- Quote from: Mechatrommer on October 28, 2023, 10:00:58 pm ---
--- Quote from: Fungus on October 28, 2023, 09:58:08 pm ---
--- Quote from: Mechatrommer on October 28, 2023, 09:32:28 pm ---good! thats "more accurate"

--- End quote ---
This still needs explaining though:
[img]

--- End quote ---
thats where turning Sinc off, or plot in dot mode

--- End quote ---

That is in dot mode...

(according to tautech)

--- End quote ---
No.

The scope menu clearly shows the scope is in Dot mode.
However this was a running capture, not one from Stop mode where many fewer dots get shown.
Yet, even with a capture we can toggle to Vector or Sinc etc modes.
There's good reason why we show full menus so to accurately display scope settings.

Mechatrommer:

--- Quote from: tautech on October 29, 2023, 01:09:29 am ---However this was a running capture, not one from Stop mode where many fewer dots get shown.

--- End quote ---
analyzing those fewer dots may reveals whether the scope showing sampled data only, or sampled data along with interpolated data, like Lecroy snapshot is combination of vector and dots, but the dots are interpolated data.

since at it, Rigol DHO800/900 cannot turn off Sinc, i searched last night.. this is :-- point on them (not to forget the other  :-+ points to be fair, but thats OT, Fungus starts to cringe
i suspect ;D) so i have to download and analyze data in PC as screenshot shows... lets analyze this "improperly designed" scope..

1.jpg = the dso respond to a "pulse" (a reality approximation to a theoretical "step") here we dont see Gibbs, only under-damped front end respond
2.jpg = reducing sample rate by enabling all channels, bingo! Gibbs Phenomenon. newbies need to be educated to avoid this delusion. or even long time users can usually forgot the fact. if not careful
3.jpg = increasing time scale to see how Gibbs represent differently
4.jpg = increasing time scale more, the "imaginary" part of Gibbs disappear, maybe got folded back (aliased) during interpolation process?
5.jpg = this is where downloadable data to PC comes to rescue. vector plot without fancy Sinc shows how the signal was sampled. no Gibbs! this what i tried to explain.
6.jpg = look closer at sampled data vectored

with PC data available, one can do further fancy interpolation (or countless amount of analysis types) if needed, but i'm not a fancy guy, so vector plot is enough for me. i'll do interpolation and judgement in my head myself. imagine even if raw/sampled data pulled from scope is the one with interpolation/Gibbs, user will not be able to further analysis correctly, such as when plotting our own FFT (7.jpg.. there's bug or misconception i know Fnd'tl should be the 1st Hm :palm:) imagine a process... sample data -> fft -> sw bw limiting -> ifft -> pull data to PC -> fft -> display.... the resulting end FFT will looks funny i suspect.

i've been searching for siglent programmability and sw/program example in pc to no available. since ds1000e or ds1000z i think. but recently i see siglent is following the path of using ni-visa driver as its API, now its a good step imho for me long time using ni-visa in rigol. lets hope there will be good sw to post process raw data from siglent's scope. as for now, i got cheap dho800/900 to play with, and its 12bits is the main reason i bite the bullet getting it, to further push boundary down the noise floor of my FFT. one funny thing i realized is i eventually hit the limit of my fft library memory points. it cannot do more than 25Mpts FFT analysis, maybe Windows is limiting memory quota for my program/library thread. so i cannot utilize fully the 50Mpts DHO900 memory. even more so for siglent with much larger memory.

since its the lowest price and already familiar with the workflow thats why DHO800 is the chosen one. siglent? maybe later when i'm rich enough to spend money for minor minor things. back to my sw, i was planning to add LA/serial decoder (from long memory data) functionality 7 years ago, which the main drawback in DS1000Z toyish serial decoding function. but then i lost enthusiasm during development and leaved my VisaDSO as it be. since i dont use serial decoder much, and i already have cloned salae 8 channels if i really need the job done. if minor upgrade/fix thats not requires very long time to do, then i come back to VisaDSO.. like few weeks ago.

with diy PC SW, there is no limit to where your imagination can go... (ahaks the marketing tone BS)... fwiw.

tautech:

--- Quote from: Mechatrommer on October 29, 2023, 07:04:51 am ---
--- Quote from: tautech on October 29, 2023, 01:09:29 am ---However this was a running capture, not one from Stop mode where many fewer dots get shown.

--- End quote ---
analyzing those fewer dots may reveals whether the scope showing sampled data only, or sampled data along with interpolated data, like Lecroy snapshot is combination of vector and dots, but the dots are interpolated data.

--- End quote ---
Want some special screenshot ?
Just ask.

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