REL #13 RTB2000, SDS2000x Plus and DSOX1000 Oscilloscopes, Episode 6c FFT Analysis

[@queuerious]

superb FFT discussion and demonstration. I've learned more from your tutorial on FFT in my RTB2004 than hours with their manual! thanks for sharing!

[@rudiselectronicslab861]

Thank you, appreciate your reaction!

[@jeanlouisjoyeux4901]

very interesting comparison and a good introduction to FFT analysys

[@rudiselectronicslab861]

Glad to hear that!

[@daveevans9809]

Can't believe you haven't got more subs but I'm sure the word will get round. You may be the only publisher on here that doesn't use "Insane"' or "It's over!" or whatever will be the next click bait meme. 🙂Keep it up, and thanks.

[@aviationodyssey1892]

Such a great educational video. Love it!

[@rudiselectronicslab861]

Glad you enjoyed it!

[@miqueles5783]

I really like this series, thank you.

[@rudiselectronicslab861]

Thanks for the compliment, appreciate it. Costs a lot of time and energy...

[@todaysfigures598]

thank you! it's a fantastic comparison

[@hallolo2]

Hi, thanks for the great video series. It helped me a lot with the purchasing decision. There's just one thing I'd like to mention. You said that the Keysight Scope would be the only one in this comparison that could calculate the phase of the FFT. However, the Siglent SDS2000X Plus Series can do that as well. While it (currently) won't display it on the scope, when you export the measurement to a .csv file it contains the Amplitude, Real and Imaginary part, and Angle of the FFT.

[@rudiselectronicslab861]

Dear Wieland, thanks for the compliment and happy it was useful to you. You are totally right about the SDS being able to save phase (angle) data for FFT (I mention it in the background comparison document that comes with these videos). But when I was discussing it in the video, I was referring only to results the devices can show on their screen. Enjoy your purchase!

[@pauldenisowski]

Hi Rudi - Very nice video! Thanks for making these. With regards to the RTB and FFT, two small points: 1) You can change the horizontal scaling of the spectrum using the horizontal knob 2) Autoset sets both the channel parameters and the FFT parameters Thanks again!

[@rudiselectronicslab861]

Thank! I think I had (1) already covered in my video. Concerning (2), yes, that is interesting, had not realised it. It is not mentioned in the FFT chapter of the RTB manual, though, and only quite limited general section (page 51). So this feature could be highlighted a bit more in the manual!

[@serwiselektroniki4638]

Hi, nice video serie about comapring, a thorough and detailed analysis will definitely allow to decide on the choice of equipment. A pity there is no rigol MSO5000 but anyway it's a great piece of work. Thanks.

[@rudiselectronicslab861]

Thanks! Yes, it would be nice to add other scopes, and the Rigol MSO5000 would be a candidate there. But, to be honest, I am reaching my limits in terms of the time it takes to make these videos, and the budget to purchase these instruments :-|

[@Markus2801A]

Thank you very much for doing those reviews on comparing different oscilloscopes! I always try to reconstruct a Wave from the FFT in mathematical terms to show my student "its working". But yes its not :-) There are so many types of implementations or lets say how the manufacturer interprets the FFT, so the goal to make the FFT understandable with a real example and measurement to prove its trueness always leads me in tweaking the input and the scales and other options in the scopes to get a proper result. I also was able to test RTB2004, DSOX and have at home the Siglent SDS2104X and the Rigol DS1054 (both function and BW liberated) :-) IT would be nice to find a Oscilloscope which does the FFT "right" :-) out of the box without the need of extensive tweaking. Greetings from Austria - stay healthy and keep up your great work!

[@rudiselectronicslab861]

Thanks. Yes, it's not always easy to do a convincing demonstration to students (not even talking of Murphy's law). But it can also demonstrate them that reality can be more complex than theory, that there are all sorts of reasons (like aliasing) why actual FFT implementation on scopes shows us different things from what we expect to see...

[@Markus2801A]

@@rudiselectronicslab861 exactly, I fully agree! The faces of the students after me explaining them FFT-Theorie (mathematically) and afterwards showing, here is the result, as we see it does not match the math! :-) And then the big question: WHY? This is also very helfpful in understanding real world and what to expect and what to get in reality ;-)

[@jeanaimarre8605]

I was about to say it’s a pity that no Tektronix in your comparison. Another comment talking about Rigol. But wait, Tektronix is a must when we talk about oscilloscope, no ? Anyhow, nice and interesting work.

[@rudiselectronicslab861]

Yes, would be nice to add a Tektronix scope to the comparison, also a Rigol (and I can think of some others, too). But there are limits both to budget and available time...

[@sarming]

The peak sorting setting on the SDS only affects the table. The peak numbers themselves are always by frequency.

[@rudiselectronicslab861]

You are right, found that out after making the video. But the fact the SDS manual says "Sort peaks by amplitude or frequency" instead of "Sorts the table by amplitude or frequency" does not help, though. But the function is no 'broken', as it is... Thanks for the feedback!

[@meindertsprang7491]

Rudi, do you know that the FPC1500 can also be set to FFT mode instead of the classical Spectrum Analyser mode? It is somewhere in the setup menu.

[@rudiselectronicslab861]

Dear Meindert, yes, I have seen that in the manual too and it’s on my (long) lift of things to further explore ;-)

[@meindertsprang7491]

@@rudiselectronicslab861 If you press the Setup button, then choose "user Preference", you can scroll down to "Spectrum" and set it to FFT. I can then set the center frequency to 20 kHz, span to 200 Hz, RBW and VBW to 1 Hz. The "sweep" time will then be 3.85 s and produces a nice defined spectrum of the 20 kHz signal with 50 Hz modulation. Same settings when set to Sweep mode takes 1000 s for one sweep! R&S should have implemented a (soft) button to be able change between FFT and Sweep mode quickly. In FFT mode, thew FPC offers a slightly better resolution and sweep with than the RTB.

[@egonotto4172]

Thanks. Nice cat.

[@rudiselectronicslab861]

Yes, often nice, sometimes not. Like a cat ;-)

[@egonotto4172]

Sorry, but not every periodic function is the sum of sine waves. This is not true, even if it is often said. The great mathematician Kolmogorov took place in 1923 and 1926 examples that the claim is false. He constructed a periodic function whose Fourier serie does not converge anywhere. Kolmogorov, A. (1923). "Une série de Fourier-Lebesgue divergente presque partout" [A Fourier-Lebesgue series that diverges almost everywhere] (PDF). Fundamenta Mathematicae (in French). 4 (1): 324-328. doi:10.4064/fm-4-1-324-328

[@rudiselectronicslab861]

Interesting, was not aware of that! We indeed seem to read in almost any document that any periodic waveform can be expressed as a Fourier series and then take that for granted, but this is apparently not universally true. That is one of the reasons we have science: to falsify (the fundamentals of the science philosopher Karl Popper)