Author Topic: Rigol Oscilloscopes With(out) Bode Plot Feature?  (Read 2262 times)

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Offline jackbob

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Rigol Oscilloscopes With(out) Bode Plot Feature?
« on: March 28, 2019, 06:07:52 pm »
Call it a gimmick or novelty, but I find the bode plot feature on these newer scopes to be quite useful. While I realize there are pieces of equipment specifically for this purpose, I think the feature is good enough for most cases and nice to have, just as FFT is a decent poor man's replacement for a spectrum analyzer. I know Dave has done a video of how to obtain crude bode plots on an oscilloscope using a function generator with a frequency sweep but really, why? I mean this is such a basic feature for any scope with a signal generator onboard, it is merely just software.

Keysight's entry-level 1000X scopes include this feature, hell even Siglent has the feature on their budget scopes, even ones without onboard waveform generators. This brings us to the elephant in the room, Rigol. Am I completely missing this feature or does Rigol not include this on their scopes? For years I have been getting by the ds1054z, an almost unbeatable scope for the money. We have scopes from Siglent today for the same price but with this feature and more. Granted, the 1054z is a bit of an older scope and I wouldn't necessarily expect this feature on such a budget scope at the time it came out, but this could have been added through firmware updates. Considering how poorly FFT was implemented on this scope, this feature couldn't perform any worse.

Jump many years later and Rigol rolls out their new mso5000 series scopes. Hard to resist for the base price, can be loaded up to $5k+ for features (we all know ways around this though), and lacks this basic bode plot feature! Rigol what gives? Really they implement all these niche but appreciated features such as power analysis but cannot implement a simple bode plotter? A scope with 4 channels, 2 wave gens, and all the hardware necessary to get the job done yet they skip this feature? WHY?? It's not even an optional add on or anything. Is this feature buried in the menu somewhere? I cannot find any mention of it in the user manual. It must not exist. This can and should be implemented in a future firmware update.

Does anyone else feel the same about this feature? Are there any threads on the forum where Rigol's engineers are known to roam and take notes?
 
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Offline David Hess

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #1 on: March 29, 2019, 05:00:38 am »
It is especially dumb for an oscilloscope which also has a built in signal generator.

But almost as dumb is discarding the phase results of the FFT function because combined with differentiation or an impulse generator, a bode plot can be generated from the transient response of a system in one shot.
 

Offline jackbob

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #2 on: March 29, 2019, 05:35:02 am »
I agree they could show the phase results in FFT just as easily. Why do most scopes leave this out? I haven't worked with any scope that offers phase results in FFT. It can't be a technicality, it must be a marketing technique. If you add all these features, especially as scopes become more powerful and capable with these features, then why would one pony up the extra $$ for spectrum analyzers or network analyzers? I am aware these silly side features are not a replacement for these pieces of dedicated equipment in certain applications. But really for the hobbyist/amateurs, these capabilities would clean the market, not everyone has endless cash for some of the more expensive specialized equipment.
 

Offline Fungus

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #3 on: March 29, 2019, 05:41:25 am »
It can't be a technicality, it must be a marketing technique.

Yep, it has to be down to marketing.

The same thing happened with Serial decoders. They used to be optional but now they're standard everywhere. Some people are still holding out on CAN bus (because that's "professional") but even that's appearing in low end 'scopes now.

I'm sure every 'scope will have Bode plots as standard soon.
 

Offline thm_w

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #4 on: March 29, 2019, 07:43:50 am »
Does anyone else feel the same about this feature? Are there any threads on the forum where Rigol's engineers are known to roam and take notes?

We don't know of any Rigol reps that actually post here. So best bet is probably contact sales, let them know you are interested in purchasing MSO5000(s), but you are concerned there is no bode plot feature and if they are considering adding it in the future.
 

Offline Mechatrommer

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #5 on: March 29, 2019, 02:09:41 pm »
you can bode plot with since the DS1052E and FG and a PC. but then if you want to trade EUR7K for that on brand name, thats fine.
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Offline EEVblog

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #6 on: March 29, 2019, 02:12:50 pm »
Keysight's entry-level 1000X scopes include this feature, hell even Siglent has the feature on their budget scopes, even ones without onboard waveform generators.

The Keysight 1000X was the first to do this. I had an original prototype unit and I thought it was one of the compelling features of the new scope.
 

Offline jackbob

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #7 on: March 29, 2019, 06:12:33 pm »

The Keysight 1000X was the first to do this. I had an original prototype unit and I thought it was one of the compelling features of the new scope.


Hmm I didn't realize this feature was so new, perhaps because it just seems so rudimentary I thought it had been on scopes for longer. Given the ease this feature could be added and the value it brings especially for hobbyists, I would have expected Rigol who used to completely own the hobbyist scope market to add such a feature.

 This makes me wonder now who got it first, Keysight or Siglent? This budget end scope market has really become quite competitive and when one rolls out a scope with specific features and specs for X dollars, it's not too much later before other brands start to follow with a similar product. In this case I wonder if Keysight was putting their 1000x series together and saw Siglents bode plot feature and thought they should include it as well.
 

Offline rstofer

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #8 on: March 30, 2019, 06:21:15 am »
I ask because I know diddly about this feature:  Is the frequency scale logarithmic?  Is the vertical scale in dog Biscuits?  Am I going to be able to physically read the values for the grid lines?

When I think Bode' Plot, I have an image burned into my brain about how the amplitude and phase plots should look.

Within it's frequency range, I rather like the way the Analog Discovery 2 (and Waveforms) creates the plot.  It looks like that mystical burned image.

It just seems to me that scope screens are too small to present a properly formatted FFT or Bode' Plot.  Given computer control and data capture, it would be easy enough to use the data and something like Octave/MATLAB to make the proper plot.

There's nothing quite like a 27" screen when it comes to plotting.  Unless it is a 34" screen...

I don't think I would spend any extra money on a scope that did FFT or Bode' Plot.  But that's just me because, obviously, other people think it is a worthwhile feature.  The DS1054Z FFT seems rather crude but it's just an entry level scope.
 

Offline nctnico

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #9 on: March 30, 2019, 06:45:49 am »
It just seems to me that scope screens are too small to present a properly formatted FFT or Bode' Plot.  Given computer control and data capture, it would be easy enough to use the data and something like Octave/MATLAB to make the proper plot.
Most oscilloscopes don't have the required accuracy to justify a very detailed FFT or Bode plot. The best oscilloscopes have a DC accuracy of around 1.5%. AC isn't specified at all except for the -3dB bandwidth. So all you'd be looking at is the limit of the ADC and analog front-end. Still Bode plots and FFTs are perfectly usable. Real circuits usually have large component variations so the FFT and Bode plots offer enough accuracy to verify whether your circuit meets the design criteria or not. Still it seems in general Rigol is not the brand to look at when looking for a good FFT feature.
« Last Edit: March 30, 2019, 07:04:48 am by nctnico »
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Offline rstofer

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #10 on: March 30, 2019, 08:14:42 am »
So, qualitative versus quantitative.  That's pretty much all you get with a scope anyway.  "It's about..."

I just wasn't interested in a linear frequency scale because the shape of the graph would be all wrong.  It wouldn't look anything like my mental image.
 

Offline nctnico

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #11 on: March 30, 2019, 08:25:08 am »
So, qualitative versus quantitative.  That's pretty much all you get with a scope anyway.  "It's about..."

I just wasn't interested in a linear frequency scale because the shape of the graph would be all wrong.  It wouldn't look anything like my mental image.
But you can still use the cursors and check the amplitude / phase at certain frequencies to see if the result matches the calculations in case the oscilloscope doesn't support a log frequency scale. I haven't played with Bode plotting on an oscilloscope yet but I would assume a log frequency scale and log amplitude scale would be supported.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline David Hess

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #12 on: March 30, 2019, 10:43:56 am »
The Keysight 1000X was the first to do this. I had an original prototype unit and I thought it was one of the compelling features of the new scope.

Cleverscope has had this feature since at least 2013 and SysComp Design has had it since at least 2006.

Tektronix DSOs had this capability 30 years ago using the impulse or step response method I outlined.  LeCroy has supported it in the same or multiple forms almost as long.
 

Offline EEVblog

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #13 on: March 30, 2019, 10:59:11 am »
This makes me wonder now who got it first, Keysight or Siglent? This budget end scope market has really become quite competitive and when one rolls out a scope with specific features and specs for X dollars, it's not too much later before other brands start to follow with a similar product. In this case I wonder if Keysight was putting their 1000x series together and saw Siglents bode plot feature and thought they should include it as well.

I'm pretty sure Siglent copied Keysight.
The Keysight was released in Feb 2017, but I was given the prototype by a guy in a trench coat in the back alley at the Electronex show in Sep 2016


 

Offline EEVblog

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #14 on: March 30, 2019, 11:05:18 am »
The Keysight 1000X was the first to do this. I had an original prototype unit and I thought it was one of the compelling features of the new scope.
Cleverscope has had this feature since at least 2013 and SysComp Design has had it since at least 2006.
Tektronix DSOs had this capability 30 years ago using the impulse or step response method I outlined.  LeCroy has supported it in the same or multiple forms almost as long.

Yeas, but they aren't the low cost bench scopes we are familiar with today.
I think some other USB based scopes with function gens also had them.
But Keysight were the first to include it in an entry level bench scope with function gen sweep.
 

Offline jackbob

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #15 on: March 30, 2019, 11:16:43 am »
you can bode plot with since the DS1052E and FG and a PC. but then if you want to trade EUR7K for that on brand name, thats fine.
Is this true? Has anyone else been able to achieve this? Although I feel the DS1052E is a bit outdated, this makes me wonder if they have this functionality on other scopes when connected to a computer. Even if I have to connect the scope to a computer, it's a bit clunky but it's better than manually adjusting function generator parameters, logging data point by point and plotting.
 

Offline vk6zgo

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #16 on: March 30, 2019, 01:14:12 pm »
Everybody loves to call amplitude/frequency sweep measurements "Bode Plots", where they are nothing of the sort.

A Bode Plot is an idealised response curve, usually repeated in both amplitude/frequency & phase/frequency forms .
They are drawn as straight lines, with 3dB points shown as sharp angles, as are the changes in phase angles.
It is a long time ago, but I remember calculating these "break points" given a mathematical expression for the required response.(Wouldn't have a clue how to do it now-------30-odd years of lack of use does that).

An amplitude/frequency sweep, on the other hand, shows the response of a real device, where the changes in amplitude are gradual.
Such sweeps seldom include a phase/frequency display.

As an old fart, I find the tendency to use sloppy terminology annoying.
By the way,"Get off my lawn!"
 
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Offline Mechatrommer

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #17 on: March 30, 2019, 02:18:53 pm »
you can bode plot with since the DS1052E and FG and a PC. but then if you want to trade EUR7K for that on brand name, thats fine.
Is this true? Has anyone else been able to achieve this? Although I feel the DS1052E is a bit outdated, this makes me wonder if they have this functionality on other scopes when connected to a computer. Even if I have to connect the scope to a computer, it's a bit clunky but it's better than manually adjusting function generator parameters, logging data point by point and plotting.
well... i'm glad you asked... http://www.eevblog.com/forum/beginners/goltek-bode-plotter-pc-sw-(for-ds1000ed-andor-hantek-dds3x25)/?topicscreen dated March 2012, but it worked on 3x25 FG only as thats what i have. any other programmable FG i believe can do as well... err, dont get DS100E just because of that thread, get the newer DS1000Z, can do as well...

Everybody loves to call amplitude/frequency sweep measurements "Bode Plots", where they are nothing of the sort.

A Bode Plot is an idealised response curve, usually repeated in both amplitude/frequency & phase/frequency forms .
They are drawn as straight lines, with 3dB points shown as sharp angles, as are the changes in phase angles.
It is a long time ago, but I remember calculating these "break points" given a mathematical expression for the required response.(Wouldn't have a clue how to do it now-------30-odd years of lack of use does that).

An amplitude/frequency sweep, on the other hand, shows the response of a real device, where the changes in amplitude are gradual.
Such sweeps seldom include a phase/frequency display.
iirc we can determine system stability from bode plot when respond is over unity (greater than one) and phase is more than 180 degree, but i dont think memory serve me well, anybody can read the literature in internet now easy. i dont use my bode plotter much, i guess it was just a demonstration that it can be done (given you have some programming skill), fwiw, ymmv.


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Offline rf-loop

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #18 on: March 30, 2019, 06:29:56 pm »
This makes me wonder now who got it first, Keysight or Siglent? This budget end scope market has really become quite competitive and when one rolls out a scope with specific features and specs for X dollars, it's not too much later before other brands start to follow with a similar product. In this case I wonder if Keysight was putting their 1000x series together and saw Siglents bode plot feature and thought they should include it as well.

I'm pretty sure Siglent copied Keysight.
The Keysight was released in Feb 2017, but I was given the prototype by a guy in a trench coat in the back alley at the Electronex show in Sep 2016

Copy what? Quite a hard accusation or suspicion.
Perhaps Keysight copied some others idea that also oscilloscope may have SFRA.
Perhaps also Siglent think same, independently of each others.  If only copy idea that oscilloscope may have SFRA is it copying. Perhaps like Nissan or Lamborghini copy Ford.

Why I think this?

IF Siglent have copied  Keysight this model perhaps then they release something total junk crap.

But because they did not copy they make something what is even some amount useful and not only for tell students that  in the world there is also "BodePlot" and studets roll they eyes.

If you look Keysight scope time of release status (attached data sheet detail) you can easy see that this is really not copied by Siglent. Exept if you think that because BMW put 4 wheels under car then Nissan copy BMW and also do same - yes this level perhaps but more I believe that both have independently same idea. SFRA / BodePlot have been as long as I remember.  Even I have owned (in history) real bit different "BodePlotter" ... Rohde&S SWOB. Perhaps Siglent get idea from R&S what is more like, as they have also copycat (not copy) some other features from R&S (clearly). 

So, if you look this Keysight data sheet from release time.. you can see 10 samples / decade  (later they have improved it bit because 10pts/decade was really like bad joke. Also it have 20Hz 20MHz limits and also it have only 1 channel.

Siglent have max 501 samples even down to 500Hz Span (1Hz step).  Example, we have quite narrow 1.4MHz  CW filter what need look... say example its width is 300Hz...  If now take exaple 1000Hz Span so that 1.4MHz is center it can do samples 2Hz steps. (what can do system with 10 samples/decade).

If have some bit more complex circuit it can also take simultaneously 3 independet out from DUT.

Who can think Siglent copycat Keysight and then result is so much different and totally in different higher level of performance SFRA in Siglent SDS1004X-E. (but it do not have internal SG)
Also freq range is depending used external SG so it can do far more than 20MHz.
Of course also Siglent SFRA performance is far below real SFRA analyzers. First thing is poor dynamic range with its ADC. So, for look and adjust example high quality IF filters where stop band need be really far far below pass band it is just impossible to look this stop band. It is not tool for this.

Attached Keysight model (release time) data sheet detail about BodePlot
Siglent copycat this?  Must have a really good ability of imagination.
« Last Edit: March 30, 2019, 09:05:56 pm by rf-loop »
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Online ebastler

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #19 on: March 30, 2019, 06:40:54 pm »
I'm pretty sure Siglent copied Keysight.
The Keysight was released in Feb 2017, but I was given the prototype by a guy in a trench coat in the back alley at the Electronex show in Sep 2016

Or this might simply mean that you don't know any trenchcoat guys at Siglent.  :P

How would you know when Siglent started prototyping this feature? It's kind of an obvious idea, once you have combined a scope and function generator in one device and look for "what's next" after you are done with FFT...
 

Offline Mechatrommer

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #20 on: March 30, 2019, 07:10:52 pm »
But almost as dumb is discarding the phase results of the FFT function because combined with differentiation or an impulse generator, a bode plot can be generated from the transient response of a system in one shot.
iirc i did play with this method while developing bode plotter, using square waves, we'll need few cycles for faithful FFT result. but the result was not as neat as classical sweep method. maybe the setup was poorly controlled.
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Offline Fungus

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #21 on: March 30, 2019, 10:13:31 pm »
This makes me wonder now who got it first, Keysight or Siglent? This budget end scope market has really become quite competitive and when one rolls out a scope with specific features and specs for X dollars, it's not too much later before other brands start to follow with a similar product. In this case I wonder if Keysight was putting their 1000x series together and saw Siglents bode plot feature and thought they should include it as well.

I'm pretty sure Siglent copied Keysight.
The Keysight was released in Feb 2017, but I was given the prototype by a guy in a trench coat in the back alley at the Electronex show in Sep 2016

Copy what? Quite a hard accusation or suspicion.

Siglent defense league!

Maybe they copied their marketing strategy, nothing technical at all.

(we were just saying this is probably a marketing decision not to do it)
 

Offline nctnico

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #22 on: March 30, 2019, 10:36:53 pm »
This makes me wonder now who got it first, Keysight or Siglent? This budget end scope market has really become quite competitive and when one rolls out a scope with specific features and specs for X dollars, it's not too much later before other brands start to follow with a similar product. In this case I wonder if Keysight was putting their 1000x series together and saw Siglents bode plot feature and thought they should include it as well.
I'm pretty sure Siglent copied Keysight.
The Keysight was released in Feb 2017, but I was given the prototype by a guy in a trench coat in the back alley at the Electronex show in Sep 2016
I'm not so sure Siglent copied Keysight. At least not after the Keysight 1000X scope was released. IIRC Siglent quickly came up with an FRA feature which performed significantly better compared to Keysight. Siglent must have been working on this for a long time.
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Offline Fungus

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #23 on: March 31, 2019, 12:25:42 am »
I'm not so sure Siglent copied Keysight. At least not after the Keysight 1000X scope was released. IIRC Siglent quickly came up with an FRA feature which performed significantly better compared to Keysight. Siglent must have been working on this for a long time.

But ... if they didn't release it then it was for marketing reasons.

When Keysight released theirs with the feature, Siglent followed, ie. they copied them.

(just like Rigol 'copied' Siglent by giving away the serial decoders as standard after Siglent did it).

 

Offline nctnico

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Re: Rigol Oscilloscopes With(out) Bode Plot Feature?
« Reply #24 on: March 31, 2019, 12:32:42 am »
I'm not so sure Siglent copied Keysight. At least not after the Keysight 1000X scope was released. IIRC Siglent quickly came up with an FRA feature which performed significantly better compared to Keysight. Siglent must have been working on this for a long time.
But ... if they didn't release it then it was for marketing reasons.

When Keysight released theirs with the feature, Siglent followed, ie. they copied them.
Did it ever occur to you that manufacturers can work on the same feature at the same time? They both have the same information about the market so it is likely managements of two different companies came to the same conclusion. You can't add a complex feature like FRA into existing oscilloscope firmware in a couple of weeks. Perhaps Siglent pushed the release schedule a bit but AFAIK Siglent's FRA feature worked quite well out of the box. This is rather unique for them so Siglent must have put a lot of effort into the development and done more testing than usual.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 


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