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Rigol HDO1000 and HDO4000 12bit oscilloscopes launched in China

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2N3055:

--- Quote from: Fungus on January 30, 2023, 04:34:02 pm ---
--- Quote from: 2N3055 on January 30, 2023, 04:12:57 pm ---It's all right to not know something..

--- End quote ---

FFT mirroring is a thing. Here's a Teletubbies video:

(skip to 5:33...)




--- Quote from: 2N3055 on January 30, 2023, 04:12:57 pm ---But you're not helping HDO1000 users by pretending there is no problem.

--- End quote ---

I'm not pretending there's no problem, just that we need to know every last setting ... and the same settings tried on other devices.


--- Quote from: 2N3055 on January 30, 2023, 04:12:57 pm ---And even if we presume basic math behind this FFT is correct, how do you use this thing?

--- End quote ---

You make sure that Nyquist is high enough for the signal you're looking at.

(Which you're supposed to do anyway)

--- End quote ---

Why are you doing this? Now you want to derail topic about Rigol ...

Of course mirroring is a thing. You didn't say that. You said spectral leakage...Which is not same. That is why I said you should stay out of this discussion. You are just repeating some terms you saw on internet without understanding.
I don't need Teletubbies video for that, thank you. I know it from school...
OTOH, that video is actually not bad for someone new to topic...

Also it is obvious that user had great problems not being able to actual set FFT parameters effectively.
That is why there were dozens of posts...

skander36:

--- Quote from: 2N3055 on January 30, 2023, 06:24:07 pm ---
Also it is obvious that user had great problems not being able to actual set FFT parameters effectively.
That is why there were dozens of posts...

--- End quote ---

If you are talking about me, I remember that I set the parameters as requested. This is why I request a specific setup.
If it was after me I can present a nice looking FFT and say : "Look how good it is!"

2N3055:

--- Quote from: Fungus on January 30, 2023, 05:48:45 pm ---
--- Quote from: tv84 on January 30, 2023, 05:17:19 pm ---Shouldn't the FFT stop at 100kHz if you have the 200kSa/s ?

--- End quote ---

You mean simply display nothing on screen above that frequency?

That's a good question. Logic says "yes"... but it would look weird and I'm sure people would complain just as loudly.  :popcorn:

I don't know what other 'scopes do in this situation - I don't own them all. It seems suspicious that they claim an "FFT frequency" at double the sample rate so I'd guess "2x upsampling followed by a low pass filter" to try and minimize the effects of mirroring. If this is the case then there's a bug somewhere...

(yes, I know "2x upsampling" already involves a low pass filter so it can be a single step in practice...)

--- End quote ---

FFT must not plot anything above Nyquist because there is nothing. That is mathematically correct.

Upsampling followed by lowpass filter is nonsense that doesn't achieve anything. Frequencies folding back are because of samples having specific sampled content at sample time... You cannot do anything afterwards. It's entropy, data is lost...

Why would 2X upsampling involve lowpass filter? Is there some new DSP opposite universe that I don't know about?

Could you please explain, because I'm genuinely confused about this?

2N3055:

--- Quote from: skander36 on January 30, 2023, 06:35:41 pm ---
--- Quote from: 2N3055 on January 30, 2023, 06:24:07 pm ---
Also it is obvious that user had great problems not being able to actual set FFT parameters effectively.
That is why there were dozens of posts...

--- End quote ---

If you are talking about me, I remember that I set the parameters as requested. This is why I request a specific setup.
If it was after me I can present a nice looking FFT and say : "Look how good it is!"

--- End quote ---

Problem is that scope does not let you set these parameters the way FFT should be set.
Also you say problem is only with 10kpts or less..
But that is a big problem, because number of points shouldn't matter. FFT is routinely done on 1024 or 512 points for that matter..
Scope at one point shows both 200 ksps/s and 400ksps for FFT and shows wrong data. No setting should produce that. Where do you set FFT points ?? Is there a setting for that?

2N3055:

--- Quote from: tv84 on January 30, 2023, 05:17:19 pm ---
--- Quote from: Fungus on January 30, 2023, 05:02:20 pm ---Yep. See video three posts up ^^^

--- End quote ---

Sorry, I spoke too soon. Then I saw the rest of the posts.

Shouldn't the FFT stop at 100kHz if you have the 200kSa/s ? That would solve the picture at 200 kSa/s and save Rigol's honor.  :)

But then, why does the 400kSa/s show the same mirroring?  :palm: 

These are the moments where you need an engineer next to the GUI programmers or in the betatesters group...

I wonder how such a bug passed the FFT QC tests?!?  :-//

--- End quote ---

It should stop at 100kHz. And it is not happening all the time.. If you put scope in Auto memory mode, it will have high enough sample rate and you won't see this..  It wasn't tested properly, it was rushed to market... I refuse to believe Rigol engineers don't know this. They were not given enough time.

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