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

--- Quote from: rf-loop on October 28, 2023, 08:34:27 am ---
--- Quote from: Mechatrommer on October 27, 2023, 05:28:08 pm --- as long as "fundamentals" is not exceeding nyquist limit, there will be no aliasing.

--- End quote ---

In my opinion, this statement is a bit false.

But of course.
When the system does not produce an alias frequency from fundamental (aka 1st harmonic) then fundamental is not aliasing.

When harmonics are downconverted by ADC these down conversion products are there. And these down converted "false" signals we call a bit carelessly aliases. This is true with all harmonics, including also 1st. 1st harmonic aka fundamental.


--- End quote ---

Many seem to forget an ADC is actually like an Impulse Sampler in the time domain (Zero order hold), or close approximation of such. This is true because the ADC produces a digital output rendering of the analog input signal at precise time interval sample points.

This along with Nyquist, produces frequency translation similar to a classic heterodyne mixer from the RF world. We utilized this Nyquist "Feature" with custom ultra-high speed Sampling CCD Convolvers (Chirp Z Transform) which operated in various Nyquist "Zones" back in 1980 for a handheld RTSA we developed.

The reverse is also true as one can employ Nyquist to "Produce" output signals from a DAC in various Nyquist frequency "zones", very powerful techniques indeed!!

Best,
Fungus:

--- Quote from: Mechatrommer on October 28, 2023, 01:27:14 pm ---
--- Quote from: Fungus on October 28, 2023, 10:17:36 am ---Turning off sinc is NOT a good idea.
--- End quote ---
i give up! You win! do whatever you like! ;D

--- End quote ---

What do you propose the 'scope should show instead?
Mechatrommer:
As you (rf loop) also agree, this is not siglent vs rigol war.. this to increase awareness.. if you dont nitpick, you should see there i put rigol name there as well.. not for tug war, but thats 2 name we usually own, and S people usually come and degraded cheaper R based on delusion. I can as well ask you to do it on r&s, lecroy, tektronix et al, for the sake of technical/theoritical/academic discussion.. but probably hi end brands implements interpolation a bit differently.. please also do so whats on your bench and convenient to you.
Mechatrommer:

--- Quote from: Fungus on October 28, 2023, 02:28:45 pm ---
--- Quote from: Mechatrommer on October 28, 2023, 01:27:14 pm ---
--- Quote from: Fungus on October 28, 2023, 10:17:36 am ---Turning off sinc is NOT a good idea.
--- End quote ---
i give up! You win! do whatever you like! ;D

--- End quote ---

What do you propose the 'scope should show instead?


--- End quote ---
what good proposal is? if only for you to deny? And you keep putting 2 contradicting statements in one post. Amazing!
Mechatrommer:
here i tried to replicate 2N3055's capture of Gibbs Effect in my DS1054Z. i dont have fast rise time 16MHz that can produce 10mVpp, but since the focus is on Gibbs Effect (whether its real or not?), the closest i can get is Leo Bodnar's pulse 10MHz @ 1Vpp. and then i figured i was actually struggling to get as low sampling rate i can get similar to 2N3055, i have to turn all channels ON and have to go up to 2us/div, reduce memory depth down to minimum 3Kpts/ch, then only i get 125MSps, but at this time/div, the cycles are too densed together to give any useful info for the purpose. so i have to dial back down 20ns/div and thats at 250MSps, thats the closest i can get. we cant set sampling rate to our heart content in Rigol, apart from reducing mem depth and increase time/div... other than that its automatic, maybe to avoid nasty Gibbs? who know?

turn on Sinc, vector plot (sinc_on.jpg)
turn off Sinc, dot mode (while running/capturing) (dot_on_run.jpg)
turn off Sinc, dot mode (Stopped to better see points) (dot_on_stop.jpg)
turn off Sinc, vector plot (sinc_off.jpg)

Gibbs effect succesfully produced in (sinc_on.jpg), but when in dot mode (dot_on_run.jpg or dot_on_stop.jpg) Gibbs dissappear, if you try imaginatively (if you dont want to try it on paper) to connect straight line between point to point in dot mode, you wont see any Gibbs effect. Gibbs only appear when Sinc interpolator is turned on in scope. do you understand what i meant before posting?

so tell me Mr sharp trained eyes Fungus (and others who have sharp eyes or brain) which signal do you like? or think its true happening on circuit?.. sinc_on.jpg? sinc_off.jpg? or dot_on_stop.jpg? or all true? because when i turn on Sinc, suddenly something on front end DSO pcb clicked and activate 8th order non-causal Chebysev?

and can any S or other brand DSO to do this test? and demonstrate here? cheers..
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