Rigol MSO5000 FFT Scripts and BUGS - Page 1
Forum section: electronics / testgear

author: BRZ.tech
author_rank: Regular Contributor
timestamp: January 01, 2022, 06:26:01 pm
content: 1. The purpose of this thread is:"Make scripts to use the FFT on the MSO5000, in any situation, and to carry out tests with the internal SG-GI/GII"2. The first case is: “Measuring the Modulation Index of AM Signal using an FFT”, using the signal generated inSG-GI/GII, and thenFFT - Math function in MSO5000 family.3.ORIGINAL CONDITION: To generate inSG-GI or GII:Carrier Sine Signal f = 1MHz, with Vpp = 500mV, and Audio Modulator Sine f = 10 KHz, with AM Depth = 80%.4. ForMeasuring the Modulation Index of an AM Signal using an FFT, I found an application note for theSIGLENT SDS 1204X-E, here:https://siglentna.com/application-note/measuring-the-modulation-index-of-an-am-signal-using-an-fft/?pdf=9065And that's exactly what we want to do, but using MSO5074 or other of family.5. TheFFT measurements in SIGLENT SDS1204X-E, for the sameORIGINAL CONDITIONsignal input conditions are:Carrier: f = 1.00MHz / -14.9dBV, LSB: f = 990 KHz / -22.8dBV, USB: f = 1.01MHz / -22.8dBV.6.The FFT measurements in MSO5074, I got here for the sameORIGINAL CONDITIONsignal input conditions are:Carrier: f = 1.00MHz / -21.17dBV, LSB: f = 990.01KHz / -29.71dBV, USB: f = 1.099MHz / -29.04dBV.7. We can see that for the SameORIGINAL CONDITION, theMSO5074 x SDS1204X-E measurements are very different.Carrier signal and LSB (Lower Side Band) and USB (Upper Side Band) are too far apart.For example, respectively, theCarrier = -21.17dBV x -14.9dBV...A difference between both measurements is(21.17 - 14.9) = 6.27dBV, or 42.08%.In my opinion this difference of6.27dBV (or 42.08%) is Absurdly High.However, when it comes to Measuring Instruments, they should be equal, or with a differencenot exceeding 5%.We are talking about Measurement Accuracy, Not an Entertainment Screen.8.Which of the two instruments: MSO5074 x SDS1204X-E, come closer to reality and accuracy?9. To replicate the essay, I suggest the quick commands onMSO5000:(Enter G2 SINE WAVE Signal 1 MHz with Modulation to CH-1) (With External Cable):(SW-Chanel-1 -> Lights up YELLOW) -> (Attenuation -> 1x) -> (Coupling -> DC) -> (More) -> (Fine <- off) -> (Menu off)(G2) -> (Wave -> Sine) -> (Frequency) -> (Set on Touch Screen -> 1 MHz) -> (Amplitude) -> (Set on Touch Screen -> 500 mV) ->(AUTO) -> (G2) ->(Settings) -> (Type -> Modulation) -> (Type -> AM) -> (Waveform -> Sine) -> (Frequency) -> (Set on Touch Screen -> 10 KHz) -> (AM Depth -> 80%) -> (Impedance -> High) -> (Menu off)Enter FFT-GII Signal to CH-1 - (SINE-1MHz-AM Modulation):(Horizontal Scale -> 5ms) -> (Trigger -> Rotate -> Stop Signal on Screen) -> (Verify -> 500MSa/s -> 25Mpts)(Vertical Scale -> 100 mV) ->(CH1 -> OFF) -> (Menu off)(Math) -> (Math2) -> (Operator -> Select -> FFT) -> (Operation -> ON) -> (AutoSetting) ->(More) -> (Unit – dBm/dBV) -> (X -> Span-Center) -> (Center -> Set on Touch Screen -> 1 MHz) -> (Span -> Set on Touch Screen -> 50 KHz) -> (Window -> Blackman) ->(Peak Search) -> (Peak Search -> ON) -> (Peak Number -> 3) ->(Table Order -> Freq Order) ->(Threshold) -> (Rotate-Function-Knob-LEFT -> Purple Line -> Around the Biggest Peak -> Until See 3 Peak Number) ->(Back) -> (More) -> (Display Lable -> ON) -> (Library -> FFT) -> (Lable -> FFT or Type Other Text) -> (Menu off)(Math) -> (Math2) ->(Scale -> Rotate-Function-Knob or Touch Screen -> 5U or 5dBV) -> (Offset -> Rotate-Function-Knob or Touch Screen -> 34U or 34dBV) -> (Menu off)(Touch Screen -> Drag the Math Table to Any Position)10.There is a suspicion that the MSO5000 SG GI/GII may be faulty, and perhaps can be fixed by RIGOL.

author: 2N3055
author_rank: Super Contributor
timestamp: January 01, 2022, 06:56:49 pm
content: What is the signal source here?Did you do same measurement with both scopes using same signal source?There was a topic some time ago that Rigol on their standalone AWG doesn't properly implement AM modulation depth, i.e. that when you set it to 50% or 100% it is not modulated to level as it should be.This might be problem with signal generator not generating proper modulation....So that needs to be checked first.

author: BRZ.tech
author_rank: Regular Contributor
timestamp: January 01, 2022, 07:09:42 pm
content: 2N3055,The ORIGINAL CONDITION in MS05074 and SDS1204X-E are the same, the picture I took from there, verify the article of SIGLENT link.Carrier Sine Signal f = 1MHz, with Vpp = 500mV, and Audio Modulator Sine f = 10 KHz, with AM Depth = 80%.I have only the MSO5074.About the other topic… Please, inform the link.Why has RIGOL not solved this flaw so far?

author: 2N3055
author_rank: Super Contributor
timestamp: January 01, 2022, 07:57:21 pm
content: Quote from: BRZ.tech on January 01, 2022, 07:09:42 pmOK so you don't have SDS1204X-E to measure same signal.You need to verify signal source first, or find another good known signal source you know it behaves correctly.This way you don't know which one is wrong: AWG modulation or scope FFT.Link is here:https://www.eevblog.com/forum/testgear/new-rigol-16-bit-function-generators-dg800900-series/msg3570478/#msg3570478Basically modulation index is not same number as would be with a proper RF generator. I own a Siglent AWG and they do it right..I also own Rigol DG1062Z but it is in my sons lab at the moment and cannot check that one. It is nice little AWG though, very clean signal for what it is.If they use same flawed algorithm, I would presume AWG is to blame for what you see.. But I don't know if someone doesn't try..I don't have MOS5000 available to try it.I have no clue why they don't fix problems. You should ask Rigol that.

author: BRZ.tech
author_rank: Regular Contributor
timestamp: January 01, 2022, 08:40:55 pm
content: 2N3055,1. Yes, I don't have the SDS1204X-E to measure the same signal. Check the link, which I copied the photo of the SIGLENT article, here:https://siglentna.com/application-note/measuring-the-modulation-index-of-an-am-signal-using-an-fft/?pdf=9065If SIGLENT made the article, it's because they know what they're doing...2. 2. As for the link provided, it is not SG-GI/GII-MSO5000. It is the AWG Rigol DG800/900:“Re: New Rigol 16-bit function generators DG800/900 series« Reply #741 on: May 16, 2021, 09:58:32 am »Quote from: TurboTom on May 16, 2021, 06:02:00 am... amplitude while the carrier stays constant when checking RF gear. I'ld say, "well done, Rigol".Yep. carrier level must not change when change modulation depth. When it is solved by this -6dB solution it meet this main principle. -6dB drop is ok compromise so noobs do not burn they circuits with peak level if "accidentally" turn AM on with high mod depth."well done, Rigol"”3. As for asking questions at RIGOL, first ask yourself here. And we'll see the results, compared to other measurements on other instruments. If it's the faulty algorithm. Does RIGOL not know this? This is impossible.4. Okay. You don't have to test one of the MSO from the MSO5000 family. But the interesting thing is to have an MSO5000 available and to use it often.

author: 2N3055
author_rank: Super Contributor
timestamp: January 01, 2022, 10:29:06 pm
content: Quote from: BRZ.tech on January 01, 2022, 08:40:55 pmI have to admit that I have a bit of trouble understanding you.So lets be clear:You can argue here as much as you can but fact is that you are comparing results from a whitepaper written by Siglent using all the Siglent equipment (which, by the way, I know it was verified to correct) to something you're doing on different equipment from different manufacturer. Analysis of that show following potential problems:1. Rigol AWG might have different behavior at same settings2. Rigol scope might have different behavior at similar settings (you won't be able to achieve same settings because of differences in scopes)3. You might have made a mistake reproducing exact same setupIf we ignore number 3. and presume you did all well, it is still unknown is it AWG or scope or both combined that are wrong.And until someone either verify MSO5000 AWG with other scope (preferably same SDS1204X-E with same settings as in that whitepaper) or check MSO5000 scope part with same Siglent AWG that was used, so we know signal is the same, and if error is still there, than we know it is scope that is measuring wrong.You cannot change two variables at once and expect to understand what went wrong.Fact that I pointed you to problems with separate AWG from Rigol is to show how Rigol doesn't understand a topic. If they used that (wrong) way of working on a standalone AWG that has only one purpose, to be signal generator, they could easily done that on MSO5000 too. Manufacturers reuse code and people doing certain specialties. So, in that light, I would be inclined to speculate that it is more likely that problem is with simplistic implementation of AWG on a scope than FFT.I don't know that for a fact but it is logical to be more suspicious of that, in light of that knowledge. But until you (or somebody else) verify this with MSO5000 and good known signal and good known scope we won't know for sure.And frankly you seem to be quite naïve. There are many occasions where manufacturers didn't know about problem because everybody seems to like to talk ad nauseam about some problems and start long rants on forums like this, but somehow writing a short E-mail to Rigol to report bug is hard. Also there are many occasions where manufacturers knew about the problem and simply decided to ignore it because it is lots of work and only few people complained about it.I don't own MSO5000 and never will. To me it is a weird scope with lots of features that look good on paper, but lack in implementation and too many real life compromises that just make it something not useful to me. Funny thing, I did own little DS1074Z before and liked the little thing. Within it's capabilities it worked well.

author: gf
author_rank: Super Contributor
timestamp: January 01, 2022, 11:14:17 pm
content: Is the carrier voltage of 500mVppthe no-load voltage, or the voltage with 50 Ohm termination?How is the signal probed?- direct connection into scope input, input set to 50 Ohm?- direct connection into scope input, input set to 1M Ohm?- high Z 1:1 probe?- high Z 10:1 probe?Is the same probing used with both scopes?dBV is not necessarily a unique specification. It can be interpreted as either dBVeff, dBVpeakor dBVpp. So dBV numbers from different origins may not be comparable, but there can be a difference of 3, 6, or 9 dB. Still both can be correct, but just interpreted differently.

author: TurboTom
author_rank: Super Contributor
timestamp: January 02, 2022, 12:40:41 am
content: Quote from: 2N3055 on January 01, 2022, 10:29:06 pmHappy New Year and ...... I dare to disagree. The DG800/900 series is an arbitrary waveform generator, not an RF signal generator. Hence, Rigol makes sure that the absolute momentary signal amplitude doesn't exceed the specified figure (voltage/level). In case of an AM signal with fixed carrier, this would be the case (by 6dB) if the carrier stays at the same level as in unmodulated operation. There has been a lot of argueing going on on that topic. In the most recent firmware revision for the DG800/900/2000 AWGs, Rigol has changed the math model (variable carrier when changing AM depth) for a reduced but fixed level carrier (6dB below unmodulated), thus limiting the 100% modulated output amplitude to the preconfigured level. IMO, this approach is valid and reasonable in case of a waveform generator, it only should be properly documented and specified. Obviously, in case of an RF signal generator, the carrier can be expected to stay constant, regardless if the signal is amplitude modulated or not.It's well possible that Rigol took the same approach in case of the DS5000's integrated AWG, but that's an assumption since I haven't got any experience with this instrument. Regarding the DG800/900/2000 series of AWGs, your bashing is not legit -- these are pretty decent instruments, especially considering the price of the entry level model after the hack.Cheers,Thomas

author: seronday
author_rank: Regular Contributor
timestamp: January 02, 2022, 03:21:40 am
content: @BRZ.techYou need to be aware that the MSO5000 Generator output voltage level is reduced by half (6dB), when amplitude modulation is selected.The User Manual makes reference to this under " Set the Modulation Depth "This change in level can be observed as follows:-Monitor the Generator output.Select Amplitude Modulation.Set the modulation level to 0 percent.Turn the modulation On and Off.I assume that this has been done so as to not overdrive the Generator output stage on modulation peaks, when the output level is set to maximum.So to reproduce the Siglent test that you refered to it would be necessary to to set the MSO5000 Generator output to 1V P/P,Regards.

author: 2N3055
author_rank: Super Contributor
timestamp: January 02, 2022, 09:20:33 am
content: Quote from: TurboTom on January 02, 2022, 12:40:41 amThomas,Happy New Year !!I certainly didn't have any intention to bash anything. I think that Rigol AWGs in 800/900 and 1000Z series are excellent generators that work well and are a great value. I really like signal sequence option on new ones and I miss that on my Siglent.What are you saying is actually confirming that problem OP is seeing might be what I'm suggesting.They chose to make it so it keeps P-P value of signal without modulation. As far as I understand, AM modulation index and AM modulation depth is correct per se, but specifying output signal level of carrier is simply not correct. If you keep enabling and disabling modulation, carrier will jump up and down, and if you set -10dBm level of signal, carrier won't be at that level with modulation on.On Siglent SDG6000X I have, AWG will reduce output signal level proper way if you enable AM modulation and it cannot achieve full signal and will keep it true to RF generator definition, as displayed and set.There are many people that use these AWG as an RF generator in lower bands. Why wouldn't they?I'm fully aware of all the compromises involved in making those instruments. If anything I haveenormous respectfor both the Rigol and Siglent engineers for making these absolutely excellent instruments for the money we can afford.They had a choice of making output level with AM modulation conform to either:1. RF gen view of constant carrier level2. AWG generalized view of output level as a level of whole signalFact is that I (and many other people) tend to look at AM modulation levels intuitively the first way (RF gen way).I rarely use it outside that context too...So while both approaches are valid from mathematical standpoint (AM modulation depthisaccurate), inmy opinion, Rigol chose wrong strategy forthis, as evidenced by many posts of people being confused by it...From technical standpoint it might not be wrong, but fromintuitive user interface standpointit is wrong.To add offense to the injury, that is only a simple calculation and displayed value issue. It could have been easily made to be user option (AM modulation level config: Constant carrier/Constant P-P ) so users can switch it to their liking.So inthiscase IthinkSiglent AWG AM level strategyis more alignedwith whatpeople expect (RF gen behavior).But to make it clear, that small issue doesn't make Rigol AWGs bad. They are excellent instruments. If you don't care about this AM level choice, they are very good value, and have many other good qualities. I do own one.. Few years ago I sold my Rigol scope, but I kept the DG100Z, even after I bought SDG6022X.All the best..

author: BRZ.tech
author_rank: Regular Contributor
timestamp: January 05, 2022, 05:50:04 pm
content: @2N3055,Thank you for replying.You affirmed:“I have to admit that I have a bit of trouble understanding you.”Ok. You don't have an MSO from the MSO5000 family. And it cannot reproduce the essay.And, I have to admit, understanding the command sequence or flowchart to get the FFT-AM on the MSO5000 is not that simple. It is necessary to go through the difficulty to reach some satisfactory result.As for the quality of the SDS1204X-E and MSO5000 are not being tested. What I want is to understand how the MSO5074 works, and trust the results of its measurements.I don't have an external SG or AWG, or the SDS1204X-E. The SDS1204X-E does not have the internal SG. There is the accessory, or you must buy a professional external SG.The MSO5000 has an internal SG, limited to SINE = 25MHz and SQUARE = 15MHz.The one I can use right now is MSO5074. Which in my opinion is excellent and functional.Just learn to use the commands in the correct sequence.@2N3055, Your comments are relevant, thank you very much.@gf,Thank you for replying.Your questions are relevant, but they are the “initial question data”, which was asked so that anyone who has an MSO5000 can reproduce the essay.Note “Item 9” of the Initial MSG.You affirmed:1. “Is the carrier voltage of 500mVpp the no-load voltage, or the voltage with 50 Ohm termination?”The MSO5000 SG G1/G2 has programmable signal output in 50 Ohm and HighZ. I fixed on HighZ. But changing to 50 Ohm, there is no change in measurement.The ORIGINAL CONDITION: To generate in SG-GI/GII in MSO5000:Carrier Sine Signal f = 1MHz, with Vpp = 500mV, and Audio Modulator Sine f = 10 KHz, with AM Depth = 80%.2. “How is the signal probed?”- direct connection into scope input, input set to 50 Ohm?- direct connection into scope input, input set to 1M Ohm?- high Z 1:1 probe?- high Z 10:1 probe?”External connection (G1/G2 to CH-1) can be done through the original Probe in 1:1. Or via 2 x BNC connector with cable.3. “Is the same probing used with both scopes?”No. I only have one MS5074 with the original probes. I don't have the SDS1204X-E.Note "item 4" of the Initial MSG:“For Measuring the Modulation Index of an AM Signal using an FFT, I found an application note for the SIGLENT SDS 1204X-E, here:https://siglentna.com/application-note/measuring-the-modulation-index-of-an-am-signal-using-an-fft/?pdf=9065”4. “dBV is not necessarily a unique specification. It can be interpreted as either dBVeff, dBVpeak or dBVpp. So dBV numbers from different origins may not be comparable, but there can be a difference of 3, 6, or 9 dB. Still both can be correct, but just interpreted differently.”@gf, The “Unit” of the FFT on the MSO5000 can be set to: “dBm/dBV or Vrms”.@gf, I read about dBV, and it's the RMS measure. See article: 0 dBV = 1 Vrms:https://reference-audio-analyzer.pro/en/v-dbv-dbu.php#gsc.tab=0@gf, your comments are relevant, thank you very much.@TurboTom,Thank you for replying.You affirmed:“... I dare to disagree. The DG800/900 series is an arbitrary waveform generator, not an RF signal generator. Hence, Rigol makes sure that the absolute momentary signal amplitude doesn't exceed the specified figure (voltage/level). In case of an AM signal with fixed carrier, this would be the case (by 6dB) if the carrier stays at the same level as in unmodulated operation. There has been a lot of argueing going on on that topic. In the most recent firmware revision for the DG800/900/2000 AWGs, Rigol has changed the math model (variable carrier when changing AM depth) for a reduced but fixed level carrier (6dB below unmodulated), thus limiting the 100% modulated output amplitude to the preconfigured level. IMO, this approach is valid and reasonable in case of a waveform generator, it only should be properly documented and specified. Obviously, in case of an RF signal generator, the carrier can be expected to stay constant, regardless if the signal is amplitude modulated or not.It's well possible that Rigol took the same approach in case of the DS5000's integrated AWG, but that's an assumption since I haven't got any experience with this instrument. Regarding the DG800/900/2000 series of AWGs, your bashing is not legit -- these are pretty decent instruments, especially considering the price of the entry level model after the hack.”Quanto à série DG800 / 900. Eu não possuo um exemplar. Não posso comentar.Quanto se deve ser documentado os parâmetros do SG para geração de sinal e medições, eu concordo com você:As for the DG800 / 900 series. I do not own a copy. I cannot comment.When it comes to documenting the SG parameters for signal generation and measurements, I agree with you:“in case of a waveform generator, it only should be properly documented and specified”.@TurboTom, your comments are relevant, thank you very much.@seronday,Thank you for replying.@seronday, your comments are relevant, thank you very much.You affirmed:“@BRZ.techYou need to be aware that the MSO5000 Generator output voltage level is reduced by half (6dB), when amplitude modulation is selected.The User Manual makes reference to this under " Set the Modulation Depth "This change in level can be observed as follows:-Monitor the Generator output.Select Amplitude Modulation.Set the modulation level to 0 percent.Turn the modulation On and Off.I assume that this has been done so as to not overdrive the Generator output stage on modulation peaks, when the output level is set to maximum.So to reproduce the Siglent test that you refered to it would be necessary to to set the MSO5000 Generator output to 1V P/P,Regards”I made your suggestions, and took the pictures, with Carrier = Amplitude = 1Vpp on MSO5074.1. Carrier without Modulation: around Vpp = 1.0359V.2. Carrier with Modulation, with AM Dept = 0%: Around Vpp = 513.12mV.Note that Carrier with Modulation has dropped almost by half, as per the User Manual: 1.0359V -> 513.12mV.3. Carrier with Modulation, with AM Dept = 80%: Around Vpp = 929.43mV. So, the Vpp of the AM modulated signal on the MSO5074 was around 1Vpp.4. The “Surprise” in the FFT measurement was to multiply by 2x the 500mV Vpp of the SG signal in the MSO5074, to 1Vpp.The FFT measurements on the SIGLENT SDS1204X-E, for Carrier = 0.5 Vpp, are (according to the SIGLENT article):Carrier: f = 1.00 MHz / -14.9dBV, LSB: f = 990 KHz / -22.8dBV, USB: f = 1.01 MHz / -22.8dBV.6. The FFT measurements at MSO5074 for Carrier = 1Vpp, are:Carrier: f = 1.00MHz / -15.15dBV, LSB: f = 990.01KHz / -23.7dBV, USB: f = 1.099MHz / -23.03dBVIt can be seen that the FFT measurements on the MSO5074, with Carrier = 1Vpp, were very close to the measurements offered by the SIGLENT SDS1204X-E test (with Carrier = 0.5Vpp -> see the article on the SIGLENT link).In the case of Carrier:MSO5074 = -15.15dBVSDS1204X-E = -14.9dBVThe difference between measurements being (-15.15 – (-14.9)) = -0.25dBV = 971.6 mV.Here, a dBV to Volt converter, enter -0.25dBV:http://www.cantwellengineering.com/calculator/convert/dBV

author: normi
author_rank: Regular Contributor
timestamp: January 07, 2022, 05:07:29 pm
content: Based on response from core when this was raised in another thread, the experiment was done with the MSO500 and a Siglent SDS 1104X-E using the SDG2042X generator. Results on both scopes were the same and in line with document. So there is no issue with the FFT on the scope.https://www.eevblog.com/forum/testgear/hacking-the-rigol-mso5000-series-oscilloscopes/msg3908075/#msg3908075The question which was left unanswered was whether this was a problem with the AWG on the scope and whether Rigol needed to fix it. I had also noted that I saw the same issue with the Feeltech 6600 AWG.So based on the responses here Rigol designed it that way as this exists in other Rigol AWGs. I would prefer to have both options on an AWG as there are clear advantages to having access to both algorithms. I am not sure what happens on the Siglent AWG when the carrier is set to the max voltage of AWG and AM modulation is done, does the voltage exceed the maximum specification.

author: BRZ.tech
author_rank: Regular Contributor
timestamp: February 20, 2022, 02:39:16 am
content: Hello everybody.On the topic under discussion, I sent the question to RIGOL's Customer Service. The questions have been received, but I still haven't had a response from them.

author: BRZ.tech
author_rank: Regular Contributor
timestamp: February 20, 2022, 02:46:03 am
content: Hello everyone, again.I'm new to MSO.For beginners, I made a script for programming the functions.I've already made some threads. I will attach the pdf.If anyone does the tests, and finds errors, let me know here in this thread, so I can correct them.If anyone has the initiative to add new scripts, put it here in this topic. And I will be able to add in the pdf. Putting the credits.All the best.