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Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)
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nctnico:
Nope. Your scope is showing the real signal. Not 'virtual' Gibbs ears. The dead-giveaway is that the signal doesn't change between vector, dot and sin x /x mode.
Fungus:

--- Quote from: wasedadoc on October 29, 2023, 01:51:51 pm ---Scope is Rigol DS1054Z enhanced to 100MHz.  The 20MHz BW limit is not enabled on any channel. CH3 is turned on but not used.  This is to enable the button to turn off sin(x)/x on the scope.

--- End quote ---

Just a note: The trick of turning on three channels on a DS1054Z to enable the menu item that says "sin(x)/x on/off" doesn't really work.

It replaces sin(x)/x with a different filter, but it's still a filter. You do NOT get raw data by doing that.

It's much better to turn off channel three and get double the sample rate.
Mechatrommer:

--- 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.




Mechatrommer:

--- Quote from: 2N3055 on October 29, 2023, 01:29:41 pm ---LeCroy scopes have Enhanced sample rate mode (ESR), that is upsampling by factor of 2, from 5GS/s to 10GS/s. That being a controversial point is irrelevant. If you don't like it,  just disable it and stop bitching about it. I also prefer not to use it, for various reasons.
--- End quote ---
10GSps quad channel, 20GSps dual channel to be accurate, and i've disabled that feature in screenshot, you can see. where did you get SDA6000 upsampling from 5GS/s to 10GS/s? its also in the setup picture cant you see? ;)


--- Quote from: 2N3055 on October 29, 2023, 01:29:41 pm ---Those who don't understand that, back to school.

--- End quote ---
who's insulting who? and who got insulted? (by facts) are you trolling so this thread can get locked? by involving your unstable emotion here? answer academically please.
Mechatrommer:

--- Quote from: wasedadoc on October 29, 2023, 01:51:51 pm ---Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

--- End quote ---
yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks! i didnt rule out the possibility of it existing... so thats why i asked for evidence. if we have yellow trace only, we could have mistakenly assume its non-causal Gibbs effect, but actually its causal real Gibbs. from picture its about 1us delay. mind to tell what filter is that? or if that feasible to put on DSO front end?
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