Products > Test Equipment
Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)
tautech:
--- Quote from: Mechatrommer on October 27, 2023, 02:25:41 pm ---imho we should turn off the questionable digital filter (sinc) feature in scope, use vector or dot plot, turn on peak detect etc and then claim it to be the most accurate. like in this capture...
--- End quote ---
:-DD
You have been busy digging out my previously posted screenshots from SDS6204A. :)
iMo:
That is the same as this example :) :
I give you 0 apples on Sunday, 1 apple on Monday, 2 apples on Tuesday, 3 apples on Wednesday.
On Thursday I calculate the average (for example), like (0+1+2+3)/4 = 1.5 and I write on your DHO804 LCD "You got from me 1.5 apples per day since Sunday".
Where the 1.5 apple on Sunday came from ??
>:D
Mechatrommer:
--- Quote from: tautech on October 27, 2023, 02:33:50 pm ---
--- Quote from: Mechatrommer on October 27, 2023, 02:25:41 pm ---imho we should turn off the questionable digital filter (sinc) feature in scope, use vector or dot plot, turn on peak detect etc and then claim it to be the most accurate. like in this capture...
--- End quote ---
:-DD
You have been busy digging out my previously posted screenshots from SDS6204A. :)
--- End quote ---
On to perusing this thread ;D https://www.eevblog.com/forum/testgear/split-from-rigols-new-dho800-oscilloscope-unbox-amp-teardown/msg5136138/#msg5136138 then i came across some "hilarious" posts imho thats difficult for me to let go ;D not particularly you, but whoever did that ;D even now i have to face one of rigol fanboyism :-DD will that made me change side? no! i'm just here, on my own side ;D cheers.
2N3055:
--- Quote from: Mechatrommer on October 27, 2023, 02:25:41 pm ---
this is trying to prove thing at it worse as we can see Sinc is messing the otherwise perfectly square wave.. and OT on that subject, he should feed the siglent while at 100MSps with > 50MHz sine or square signal instead of 16MHz arduino clock, aliasing guaranteed! whether Sinc is turned on or off. but then it seems even "aliasing" can be confusing to some people discussing it. cheers.
--- End quote ---
Could you please stop twisting what people said and misrepresenting data? Please?
You are taking images I made for specific purpose with very specific set of parameters to illustrate something.
Then you use that image and say it is something else and babble about evil Sinc reconstruction filter..
It has been explained in 1948. Long ago..
What I have shown is what happens when you undersample square wave signal, how it looks.
I used 16 MHz deliberately to illustrate point of very common signal (Arduino clock), being square wave, will have much larger frequency content of 16 MHz. This is common mistake with beginners, they buy 100 MHz BW scope to look at 50 MHz square wave because it is only 50 MHz, right.
With square wave, how much frequency BW is there in signal is visible in rise/fall time of the signal.
You can have square wave signal that has repetition frequency of 1 kHz, that will have 4GHz BW of spectrum..
16 MHz square wave (with 30ps edges) will have harmonics into gigahertz range. Any of these harmonics above nyquist will alias. And then at reconstruction will be mixed back into waveform as lower frequencies, distorting pulse shape.
Undersampling will also result in not enough timing accuracy for digital triggering. That will result in trigger jitter.
So combine that with changed pulse shape and you get that shape.
Scope cannot violate math and physics. But it is not ideal representation of infinite functions.
In attachment:
10 MHz square wave on:
Keysight 3104T : 1GHz full BW 1ns/div
nctnico:
--- Quote from: Mechatrommer on October 27, 2023, 02:25:41 pm ---
--- Quote from: iMo on October 27, 2023, 02:03:10 pm ---You cannot get those ears before the rising edge starts to rise in a real hw system.
You see it on the LCD display because the sinc interpolation has been used to interpolate between couple of sampled points as I wrote above. No FFT or any miracles are involved.
If you looked on raw data (off the memory after the ADC sampling) you would not see the ears before the start of the rising edge of the signal (for example).
--- End quote ---
yes this is exactly my point. i think when we present educational materials in public we should be careful by removing other factors that may mess up the subject we are discussing. the issue was "accurate representation" of the actual signal... imho we should turn off the questionable digital filter (sinc) feature in scope, use vector or dot plot, turn on peak detect etc and then claim it to be the most accurate. like in this capture...
--- End quote ---
No. Dot and vector mode will show a signal which is even further from what the signal looks like in reality. As I wrote before: if you want to prevent Gibb's ears then make sure the signal has a limited bandwidth.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version