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| Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding) |
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| Martin72:
--- Quote ---That is why I kepp repeating that DHO800 samples properly and DHO900 does not unles in very limited usage scenario. DHO800 with 100 MHz BW should be largely immune to this. Unless you manually reduce sample rate or memory length at long timebases. --- End quote --- Like this. |
| Fungus:
--- Quote from: Mechatrommer on October 26, 2023, 09:18:23 pm --- --- Quote from: Fungus on October 26, 2023, 08:59:22 pm ---that's sin(x)/x for you. --- End quote --- yes i provided the link in my post. sin(x)/x is a highly theoritical and mathematical. iirc i read long ago that you cannot reconstruct back the sampled real signal back on monitor the way its appeared on electrical circuit if you dont do infinite terms reconstruction --- End quote --- Using only the central part of the sinc function doesn't help but the main problem is lost harmonics due to limited bandwidth. Those harmonics are what keeps the line flat before/after the pulse. |
| tautech:
--- Quote from: Martin72 on October 26, 2023, 09:37:22 pm --- --- Quote ---That is why I kepp repeating that DHO800 samples properly and DHO900 does not unles in very limited usage scenario. DHO800 with 100 MHz BW should be largely immune to this. Unless you manually reduce sample rate or memory length at long timebases. --- End quote --- Like this. --- End quote --- Stock or hacked ? |
| iMo:
There are 4 things not to be mixed here: 1. the "aliasing" creating the fake artifacts/spurious (caused by hw&sw because of "BW vs. sampling rate") 2. the "sinc" function used for "creating the nice pictures" via the "sinc interpolation" as seen on the LCD screen (each discrete point sampled is multiplied by sinc function and all that results are added, thus you get "additional points in between", you draw them all on the screen thus you see a solid line instead of just several sampled points, like 5 points for example) 3. the process of a "reconstruction/filtering of a square wave" with help of FFT, like sqrwave->fft->filter->ifft->sqrwave 4. the "ringing" of the hw circuitry (caused by steep filters, unstable circuits, impedance mismatch) Edit: typos.. |
| 2N3055:
--- Quote from: Fungus on October 26, 2023, 09:37:43 pm --- --- Quote from: Mechatrommer on October 26, 2023, 09:18:23 pm --- --- Quote from: Fungus on October 26, 2023, 08:59:22 pm ---that's sin(x)/x for you. --- End quote --- yes i provided the link in my post. sin(x)/x is a highly theoritical and mathematical. iirc i read long ago that you cannot reconstruct back the sampled real signal back on monitor the way its appeared on electrical circuit if you dont do infinite terms reconstruction --- End quote --- Using only the central part of the sinc function doesn't help but the main problem is lost harmonics due to limited bandwidth. Those harmonics are what keeps the line flat before/after the pulse. --- End quote --- Correct! And keep the top flat too.. And somebody mentioned infinite series to properly reconstruct. That is not needed as soon as you reach resolution of screen, noise floor or step response specifications of the scope. |
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