Products > Test Equipment
Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)
<< < (32/48) > >>
2N3055:

--- Quote from: Mechatrommer on October 29, 2023, 01:59:41 pm ---
--- Quote from: 2N3055 on October 28, 2023, 08:23:21 pm ---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.

--- End quote ---
sorry i miss this post... i was distracted by other posts ;)

from eyeballing your picture, sampling at 25MSps, nyquist limit is 50MHz, but you claimed 200MHz limited. by theory, its should already violates nyquist law and unable to reconstruct, yet you showed perfect reconstruction, somethings not right. is your scope can switch down to 50MHz BW at front end? i'm unable to make conclusion, not enough data and something not add up, such as....

in your other "properly designed" scope, even 100MSps sampling on "properly cutoff" 200MHz scope, it cannot reconstruct 1MHz square accurately, we got nasty Gibbs! can you answer why? before i can make firm conclusion. here comparison:

1) sampling 10MHz square, 25MSps = perfect
2) sampling 1MHz square, 100MSps = bad
why? please elaborate. i suspect you hide some setup i'm not aware of... you didnt explain anything in your post where i usually linked.





--- End quote ---

Stating that I'm hiding things is offensive, especially because it is your refusal to try to read and understand what other people are saying.
I'm not hiding a thing, you pompous baboon...

As I explained one is made with dot mode, other one is with Sin(x/x) interpolation...

Do you, in your infinite wisdom and omnipotent knowledge know why it was possible?




ebastler:

--- Quote from: Fungus on October 29, 2023, 02:53:40 pm ---[...] we know that "Gibbs" doesn't happen in a circuit.
Pre-ringing might, but that's not "Gibbs".

--- End quote ---

Prey tell, what is the difference? If we filter a square wave to let only its fundamental and a couple of harmonics pass, and do so with a linear-phase lowpass filter -- in which way is the output signal not a direct demonstration of the Gibbs phenomenon?
rf-loop:

--- Quote from: 2N3055 on October 29, 2023, 02:59:48 pm ---
--- Quote from: Mechatrommer on October 29, 2023, 01:59:41 pm ---
--- Quote from: 2N3055 on October 28, 2023, 08:23:21 pm ---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.

--- End quote ---
sorry i miss this post... i was distracted by other posts ;)

from eyeballing your picture, sampling at 25MSps, nyquist limit is 50MHz, but you claimed 200MHz limited. by theory, its should already violates nyquist law and unable to reconstruct, yet you showed perfect reconstruction, somethings not right. is your scope can switch down to 50MHz BW at front end? i'm unable to make conclusion, not enough data and something not add up, such as....

in your other "properly designed" scope, even 100MSps sampling on "properly cutoff" 200MHz scope, it cannot reconstruct 1MHz square accurately, we got nasty Gibbs! can you answer why? before i can make firm conclusion. here comparison:

1) sampling 10MHz square, 25MSps = perfect
2) sampling 1MHz square, 100MSps = bad
why? please elaborate. i suspect you hide some setup i'm not aware of... you didnt explain anything in your post where i usually linked.






--- End quote ---

Stating that I'm hiding things is offensive, especially because it is your refusal to try to read and understand what other people are saying.
I'm not hiding a thing, you pompous baboon...

As I explained one is made with dot mode, other one is with Sin(x/x) interpolation...

Do you, in your infinite wisdom and omnipotent knowledge know why it was possible?

--- End quote ---

And, to Mechatrommer.

This dots mode, SARI (Sequential Acquistion Random Inteleaving), (not same as LeCroy RIS ut its litlle cousin) have explained and handled in many threads over years when we have handled these things about  Siglent scopes.

So you need not even think yourself, just look old threads. They ara allthere and multiple times and places.

Also many years ago here.


Sorry sides are finnish language but if you look images 9 and 10...(note signal frequency and samplerate)  perhaps you hit it.
And note. this old oscilloscope was quite slow in zoom mode and tb (but also this slow update give it better visible what happen there
in random interleaved sequential acquisition (interleaving happen due to wfm/s speed where in same frame is overlayed many acquistions. In image 10 there is red highlighted ONE acquisition... and if scope is now faster etc there can be so many acq on one image frame that it looks nearly continuous line. 
Mechatrommer:

--- Quote from: 2N3055 on October 29, 2023, 02:59:48 pm ---Stating that I'm hiding things is offensive

--- End quote ---
i wrote "i suspect"


--- Quote from: 2N3055 on October 29, 2023, 02:59:48 pm ---As I explained one is made with dot mode, other one is with Sin(x/x) interpolation...

--- End quote ---
oic, so you are comparing elephant to apple then... i got distracted again... in that case... my answer is...

1) there is no Sinc in dot mode, no wonder! there is no "reconstruction" actually happened in there, its just try to overlap REAL sampled data too many times, of course no Gibbs effect! read nctnico post. or even literatures i've provided earlier. Gibbs only happened when you turn on fancy interpolation such as Sinc. when we talk about "reconstruction", it means Sinc interpolation. not overlapping real data to many times, thats statistical. different animal! no Sinc, no "reconstruction" (interpolation) period. sorry if you dont understand that earlier.

2) now 2nd pic Sinc is turned ON (5GSps), but 1st pic not (25MSps), thats why i said comparing elephant to apple. my answer is... at 2nd picture, at 5GSps is 0.2ns samples interval, that means 500 points for each cycle, you showed 5 cycles, meaning 2500 points, that means more dots than your monitor can handle, lets just assume for simplicity the dots are 1080 dots filling your monitor. even if there is Gibbs, its too small to see the interpolation on sub-pixel level ;) do you have any idea what you are posting?



here what i suggested for you to do earlier.... check my challenge posts earlier. dial back to where you got the gibbs effect like in this picture you showed here...



screen capture it again to show the gibbs effect as reference... and then.... this is the most important part you need to get right.... change your scope to Sinc OFF, dot mode ON, and single trigger it, until it triggered and stopped. so we can see few points on screen paused, not overlapping around. and do the 2nd capture, and post here again for comparison and analysis... cheers.

here an example of the 2nd capture i need, like tautech have made... (i would love to see same time scale as the one you got the gibbs effect above 200ns/div)



or like this as an example except i need it at 200ns/div same as gibbs effect setup above.. except the settings i've mentioned.


wasedadoc:

--- Quote from: nctnico on October 29, 2023, 02:39:14 pm ---For the umpteenth time: Gibbs ears are never in the actual signal. They are a digital filtering artefact from sin x / x that can show up on the display of a DSO. But Gibbs ears are never present in a real world signal you feed into a DSO. So you can't make Gibbs ears appear by performing any kind of operation on a real signal.

--- End quote ---
Nonsense.  Digital filtering and sin(x)/x are not the only ways to create Gibbs ears. I no longer have access to an analogue Cathode Ray Oscilloscope, but before 1980 (when Digital Sampling Oscilloscopes were but a gleam in someone's eye) I could observe the same effect when passing video test signals through a low pass filter and looking at the result on a Tektronix waveform monitor. (Similar to one in the photo.)
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod