I'd be curious if all those (non-harmonic) spurs in the screenshot by mawyatt are actually still there if you download the data to a PC and do the FFT offline. I seem to recall that the FFT mode on the DHO4000 that Martin tested did some very weird resampling, potentially resulting in similar artefacts? I think it also showed the wrong units for the RBW. No units at all on the new one?
I'd be curious if all those (non-harmonic) spurs in the screenshot by mawyatt are actually still there if you download the data to a PC and do the FFT offline. I seem to recall that the FFT mode on the DHO4000 that Martin tested did some very weird resampling, potentially resulting in similar artefacts? I think it also showed the wrong units for the RBW. No units at all on the new one?
Those artifacts came directly from DHO814, as same source (AWG) was used for both scopes. I would expect they should show in data download as well, since they are displayed on screen, unless something really strange is going on with the FFT signal processing and/or display processing. Like 2N3055 mentioned we don't have a lot of direct control of the FFT engine it's very hard to compare and understand what's going on.
Those artifacts came directly from DHO814, as same source (AWG) was used for both scopes. I would expect they should show in data download as well, since they are displayed on screen, unless something really strange is going on with the FFT signal processing and/or display processing. Like 2N3055 mentioned we don't have a lot of direct control of the FFT engine it's very hard to compare and understand what's going on.
I was asking specifically because something really strange seemed to be going on with the FFT on the DHO4000 on some settings. And I don't know if that was ever explained/fixed.
From memory, I can confirm that the FFT function of the 804 is no different from the 4204.
I just ran an FFT of a 10khz sine wave from the demo board, pictures to follow.
I can't find an Average function in the menu, so I guess it won't exist.
I just activated peaksearch, max 15 points, it doesn't matter where I put the threshold, all peaks "gather" around the 10khz fundamental.
It may be that the signal from the board is simply bad.
There's a average option under Menu button as Horizontal, Acquisition, Average. This seems to do an average with the waveform before FFT. We got this to work and this is the FFT result. No luck with Cursor Peaksearch in FFT tho. The Siglent does the FFT average after the FFT we believe, more like a SA.
The DHO4204 also has no average mode for FFT.
We do have the DHO814 and can say the FFT implementation is not quite there for our professional use, the SDS2000X+ implementation is useful and we have both DSOs with "hands on".
Thank you for demonstrating the difference between a measurement vs. a mess of noise and interference.
If we try to compare the two screenshots, we have all the information on the Siglent: FFT-sample rate, FFT-length and the Averaging mode. For convenience, we also get the frequency step - and in future versions of the FW we'll also get the RBW, which depends on the window function. About the only useful window for SA applications is Flattop, so we have to multiply the frequency step by ~3.8 and get a RBW of ~362 Hz in this case.
By contrast, the Rigol shows a much lower sample rate and claims a RBW of "20" - whatever that means. If we assume that the scope actually uses its maximum of 1 Mpts FFT, then the frequency step is about 30 Hz. How can we get a RBW of 20(Hz?) under these conditions? Only explanation could be the rather useless rectangle window, which can't be used for accurate measurements at all and doesn't have a constant RBW either - at the border between frequency bins it can be even much worse than a proper window function.
We can see the excessive noise and high internal spur levels. It does not look like it would measure the individual harmonics correctly. Considering the enormous difference in RBW (362/20), the dynamic appears to be inferior too. And don't forget, the Siglent is just an 8 bit DSO!
But then again, all this does not matter - it's incredibly fast after all!
Thank you for demonstrating the difference between a measurement vs. a mess of noise and interference.
If we try to compare the two screenshots, we have all the information on the Siglent: FFT-sample rate, FFT-length and the Averaging mode. For convenience, we also get the frequency step - and in future versions of the FW we'll also get the RBW, which depends on the window function. About the only useful window for SA applications is Flattop, so we have to multiply the frequency step by ~3.8 and get a RBW of ~362 Hz in this case.
By contrast, the Rigol shows a much lower sample rate and claims a RBW of "20" - whatever that means. If we assume that the scope actually uses its maximum of 1 Mpts FFT, then the frequency step is about 30 Hz. How can we get a RBW of 20(Hz?) under these conditions? Only explanation could be the rather useless rectangle window, which can't be used for accurate measurements at all and doesn't have a constant RBW either - at the border between frequency bins it can be even much worse than a proper window function.
We can see the excessive noise and high internal spur levels. It does not look like it would measure the individual harmonics correctly. Considering the enormous difference in RBW (362/20), the dynamic appears to be inferior too. And don't forget, the Siglent is just an 8 bit DSO!
But then again, all this does not matter - it's incredibly fast after all!
FFT has always been an Achilles heel of cheap Rigol scopes if I'm not mistaken. Also, the screenshots are comparing a 500€ scope with a 1500€ one (assuming 4 channels in both cases). For many, that's peanuts. I don't work in an engineering environment, but, for my job, 1000€ is peanuts if it gets more work done, faster and more reliably.
For a hobbyist that can be the difference between 1 year of savings and 3. That's 3 years without a scope. If you extend that to the multimeters, power supply, AWG, logic analyzer, soldering iron, lab computer etc. it gets out of hand pretty fast. Ask me why I know.
There are a lot of problems, IMHO, with the DHO900, which roughly amounts to paying more for the same, as neither the bode plot nor LA work properly.
But the 800 is really good. It's cheaper than all the alternatives, Siglent, GWInstek or Micsig, its basic functionality is good, high resolution, reasonably low noise, fast interface, touchscreen, mouse support, HDMI out, fast data out to PC, good web interface, and a lot of other stuff.
I really don't get the hate. I mean, user 2N3055's criticism to the DHO900 is well deserved, I think. I would be really pissed with the FRA myself.
But why bash a bottom-of-the-barrel scope (in terms of it's price) comparing it with scopes 3 times (or even 7 with the 2000HD) the price?
The software is not finished, indeed, but everyone expected that, because that's how Rigol operates, at least with their entry-level scopes.
So, yeah, it's the best standalone scope you can buy for <500€. And yes, I don't think anybody would chose this over an SDS2000X+ or HD.
FFT has always been an Achilles heel of cheap Rigol scopes if I'm not mistaken.
FFT has always been an Achilles heel of cheap Rigol scopes if I'm not mistaken. Also, the screenshots are comparing a 500€ scope with a 1500€ one (assuming 4 channels in both cases). For many, that's peanuts. I don't work in an engineering environment, but, for my job, 1000€ is peanuts if it gets more work done, faster and more reliably.
For a hobbyist that can be the difference between 1 year of savings and 3. That's 3 years without a scope. If you extend that to the multimeters, power supply, AWG, logic analyzer, soldering iron, lab computer etc. it gets out of hand pretty fast. Ask me why I know.
There are a lot of problems, IMHO, with the DHO900, which roughly amounts to paying more for the same, as neither the bode plot nor LA work properly.
But the 800 is really good. It's cheaper than all the alternatives, Siglent, GWInstek or Micsig, its basic functionality is good, high resolution, reasonably low noise, fast interface, touchscreen, mouse support, HDMI out, fast data out to PC, good web interface, and a lot of other stuff.
I really don't get the hate. I mean, user 2N3055's criticism to the DHO900 is well deserved, I think. I would be really pissed with the FRA myself.
But why bash a bottom-of-the-barrel scope (in terms of it's price) comparing it with scopes 3 times (or even 7 with the 2000HD) the price?
The software is not finished, indeed, but everyone expected that, because that's how Rigol operates, at least with their entry-level scopes.
So, yeah, it's the best standalone scope you can buy for <500€. And yes, I don't think anybody would chose this over an SDS2000X+ or HD.
BTW the SDS2000X+ was available on sale for ~$1000 awhile back, good deal if acquired. Maybe this sale will reappear!!
I agree with you that cheap scopes don't have unlimited development budget..
And I can see that it can see as bashing when someone has large list of problems to complaint about.
In addition to that, I'm old enough that I remember well how it is if you simply cannot afford 50€ more..
Problem is:
DHO4000 that is NOT cheap scope has equally bad BODE plot and FFT implementation as cheap DHO900/800.
Actually Rigol here developed a common platform. If they make excellent FFT for DHO4000, users of DHO800 could get same excellent FFT.
This is happening with Siglent: many features from Siglent's 10000 € scopes are available on much cheaper touchscopes...
Also cheap GW-Instek has very good FFT implementation, and slightly more expensive model has full realtime spectrum mode, well implemented.
Trust me, low price is not reason for shoddy FFT implementation.
So if all the problems, and unknowns are put together, DHO800 is not best scope you can buy today for 500ish €.
12 bit makes not such a big advantage to trade off that for many other (maybe necessary stuff, people need to decide for themselves what they need) that is missing or does not work well yet.
It does have capability to become good buy, when Rigol actually makes it work properly.
I can see future in which that statement might be true. But right now, today, no.
Of course, people, fully aware of current unfinished status, might chose to consciously buy it in this state of development and simply wait for as long as needed for Rigol to debug and finish it. We all have our own will, priorities, etc. But make sure you understand you are buying unfinished product and sort of promise that Rigol will eventually finish it in due time. If that is OK with you, it's perfect.
I must admit I tend to project a different perspective: I cannot afford to have a measurement instrument that I cannot trust. Even with very expensive instruments I sometimes measure with two different ones to verify.. Keysight has bugs too... R&S and Tek too...
My experience have proven that it is best to avoid ANY product for at least 1 year after initial release, if you actually need to depend on it...
With that in mind, my opinions are obviously influenced by that.
Best,
Siniša
BTW the SDS2000X+ was available on sale for ~$1000 awhile back, good deal if acquired. Maybe this sale will reappear!!
Since "Best" and "Worst" are highly subjective, we tend to refrain from such, and our "Limited" opinion, limited in the sense we've only had a week to play around with such, the DHO814 has shown to be a good performer for General Purpose tasks, and has some unique/interesting properties that one might find useful.
Best,
And I'm not quite sure what should someone with 500 bucks to spend learn from it.
The actual comparison is still to come....
What I don't like is that "RBW" has no unit of measurement.
You can only change the vertical offset position of the FFT with a button, if the menu is active and you have selected the offset there.
Outside of the menu, you can neither move the FFT up or down with the vertical knob, nor are the 2 action buttons responsible for this, they change span and center.
Only with the fingertouch you can change the position.
No luck with Cursor Peaksearch in FFT tho.
how do you know its boxcar averaging?This is quite easy: When doing a single shot trace of preset sample count and analyze the individual samples, you can easily see the quntization of the values (like the "bins" in a histogram). At 1.25MSa/s, 1V/div you will find a quantization of approx. 2.31mv, which, assuming a quantization of 12bits (as per Rigol's specs), results in a total peak-to-peak range of approx. 9.5V which easily matches the 8 vertical divisions (8V) of visible vertical range.
The same test with a sampling rate of 100kSa/s has a quantization of approx. 0.2875mV which leads to a resolution in the ballpark of 15 bits. Since in a single shot, the calculation of a classic "isotemporal" average isn't possible, and the sampling engine itself can still be kept running at its "native" speed, it's a reasonable approach to average the "raw" samples that fall between two "shadow memory" (software) samples, into each adjacent s/w sample, resulting in the observed increase in resolution. And that's just boxcar averaging.
So to cut a long story short, just the fact to find a higher than hardware resolution in down-sampled single shot traces indicates that some kind of boxcar averaging has been applied to decimate the ADC raw data.
...
I think people are confusing the several "sample rates" within a scope. The ADC sampling rate and acquisition sampling rate (which is the data stored to memory) are not always equal. And what happens between those steps is not consistent between difference scopes/brands.
The megazoom "issue" that you've pointed to (out of context) is those scopes reducing the acquisition sample rate when in non-8bit modes, (peak detect, averaging, high resolution) as the acquisition rate changes to fill the available aquitision memory (keeping the horizontal timebase the same). The ADCs keep running at their full rate for all acquisition modes, just as the Rigol do, tuning on more channels increases the multiplex to the ADCs and drops the per channel ADC sample rate (XXGS/s to 0.5*XXGS/s).
switchabl is correct that the ADC sample rate is determining the peak detect capture window (unless some scopes have analog domain peak detect?).
With "normal" sampling configuration, the DHO900 is actually boxcar averaging when the "Shadow Memory Sampling Rate" is lower than the ADC rate which apparently stays the same all the time (only activating additional channels multiplexes this sample rate over the enabled channels). See here: https://www.eevblog.com/forum/testgear/rigol-dho804-test-and-compare-thread/msg5109618/#msg5109618how do you know its boxcar averaging?
... provided that Siglent wants to play this game at all.