Products > Test Equipment
SDS800x HD vs DHO800x FFT
tautech:
--- Quote from: cyo3fff on July 14, 2024, 09:11:28 pm ---One of the main feature of the scope should be good and fast FFT cause I need to use it as a kind of spectrum analyzer for EMC debugging.
Coming back to my question, is there anybody with a SDS800x HD (particularly SDS824x HD) who can help me with FFT refresh rate (how many fps it has for the above test case)?
--- End quote ---
Lake a proper analyzer, sweep speed is related to the settings you make.
Points, Span and Averaging settings provide speed or precision, pick your poison.
There are many examples of FFT use here:
https://www.eevblog.com/forum/testgear/sds800x-hd-review-demonstration-thread/
However these low cost DSO's don't provide a proper EMI mode like for example the SSA3000X Plus range which have preinstalled the many EMI standards and their respective level limits.
SSA3015X Plus is a good model for these LF analyser needs.
Martin72:
--- Quote from: cyo3fff on July 12, 2024, 04:51:43 pm ---Second, can you detailed a bit your thought (above)? What is better on SDS800x than in DHO800?
--- End quote ---
First would be the partially faulty windows of the FFT function, here a user had proven that they could be easily corrected, but actually this is Rigol's job to do this.
Secondly, the Rigol, like all Rigol models, lacks useful additional functions such as average and peak detect.
At least average should be "mandatory".
This would also be easy to solve if rigol were to attach importance to it.
Let's get back to your main concern, the measurement of "speed", the FPS.
I still don't quite know what you mean by that, as you mentioned realtime spectrum analyzers as a comparison.
This is a different technique behind it, the FFT function in a scope is, as the name suggests, a function, calculated mathematically.
This cannot be done/displayed in real time per se.
The "speed" then stands and falls with the number of points, the time base and the memory.
Just as an example, if the time base is set to 100ms/div in order to keep the RBW small, for example, an acquisition takes at least 1 second.
Then there is the calculation and finally the display of the function, i.e. either way you would be miles away from your 60fps.
If I were you, I wouldn't get stuck on that, instead I would focus on other qualities.
Nevertheless, I can make an FFT according to your specifications.
Fungus:
--- Quote from: cyo3fff on July 12, 2024, 04:44:43 pm ---Thank you for your comment. Believe it or not, one of the main reason I give DHO804 away was...it smell! It has a very steep plastic smell and I think I'm a bit allergic to that cause if I leave it in the lab for few days, I can't stay there...so it was something serious for me.
--- End quote ---
That completely goes away after a week or so.
(OKl, I left mine powered on for a week in a spare room so it was warm so YMMV but the smell definitely goes away)
No idea why they chose that plastic. Is it still the same in new ones...?
Fungus:
--- Quote from: Martin72 on July 14, 2024, 10:10:15 pm ---Let's get back to your main concern, the measurement of "speed", the FPS.
I still don't quite know what you mean by that, as you mentioned realtime spectrum analyzers as a comparison.
This is a different technique behind it, the FFT function in a scope is, as the name suggests, a function, calculated mathematically.
This cannot be done/displayed in real time per se.
--- End quote ---
There's a big difference between doing the math 60 times a second and doing it 6 times per second.
The Rigol may have a simplified FFT but it is fast.
cyo3fff:
--- Quote from: Fungus on July 15, 2024, 06:21:12 am ---The Rigol may have a simplified FFT but it is fast.
--- End quote ---
Hello Fungus,
Thank you for answering to my question or at least to try to answer briefly.
What I liked much to Rigol (DHO804) was its FFT speed and could compare it with the old 1054z which has a"joke" FFT in terms of speed! It take a loooot of time to do even a "few points" FFT therefore I cannot call it even close to "real time".
Just to align with everybody here, particularly in this case, by "real time" I mean at least 25fps or if you like, FFT calculations/second.
I know that this not "real time" such it is with a real time spectrum analyzer which can do a full span measurement in 1us or so but it is all right for my particular needs.
So, one conclusion is that for the same FFT settings, DHO804 (Rigol) is "way faster" than SDS824x HD.
Am I getting right? Because this is one of my main concern.
Thank you.
BR,
Cristian
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