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Rigol HDO1000 and HDO4000 12bit oscilloscopes launched in China

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Fungus:

--- Quote from: 2N3055 on February 12, 2023, 11:52:36 am ---But it does look weird...

--- End quote ---

It looks typical of most FFT images on the web.

eg. https://www.gaussianwaves.com/2020/09/window-function-figure-of-merits/

As you say, it's probably related to number of bins/number of sample points in the FFT.

Alex-lab:
Hi, Anybody knows, if that HiRes issue was fixed in available FW updates? 02.04? Thanks.

switchabl:
The "flattop" screenshot definitely looks weird. At first glance it might look like "a" windowed FFT. But look closer:
- It is nothing like a flattop window. A flattop produces a wide main-lobe and the side-lobes shouldn't have a smooth envelope.
- Why do we see wide side-lobes at all? Has the number of points suddenly dropped? The RBW display hasn't changed but unfortunately that is bugged anyway (it seems to be off by a constant factor of 1000 though; that would suggest we are still at 1 Mpts, the maximum according to the datasheet).
- Look at the main-lobe again. It actually hasn't changed much at all, it is still very sharp. And so are the harmonics. So we must still be at full resolution.

Maybe there is just a typo in the formula for the window function.  :-// It is definitely possible to construct a window that behaves like this (for example take a "normal" window function and superimpose it with a low-amplitude, much narrower window), but you wouldn't really do that on purpose.

2N3055:

--- Quote from: Fungus on February 12, 2023, 11:59:51 am ---
--- Quote from: 2N3055 on February 12, 2023, 11:52:36 am ---But it does look weird...

--- End quote ---

It looks typical of most FFT images on the web.

eg. https://www.gaussianwaves.com/2020/09/window-function-figure-of-merits/

As you say, it's probably related to number of bins/number of sample points in the FFT.

--- End quote ---

No it does not.

If you look at images on internet (wikipedia for instance), they demonstrate windowing with 11 or 13 sample points..
That is why you see something similar... With 1 million points FFT you don't see it.

And if I had to choose what it looks like it looks more like Parzen window with 11 sample points......

Because of all that i presume there is some "magic" happening with Rigol's FFT choice of how many bins it uses automatically...

Also one thing to note: They state RBW : 4.999m  ???????? What is that ???

FFT is definitely buggy and to me not finished. Few critical control variables user cannot control, and are not reported. 

Njk:
Looks like FFT is still a toy function in any scope. It's not for measurements, it's just for reference. The values for SNR or dynamic range are not provided. The only related parameter in the spec is channel isolation, which is of 1:100. That's 40 dB, so anything on the FFT chart that is below that level (-60 dB, -100 dB, whatever) is just FYI. Accuracy is not officially specified. The most fierce debates are usually about toys  :)

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