Rigol MHO900 Test/Review (MHO984)

[Martin72]

Hi,
As announced, here is a dedicated thread for the Rigol MHO984, as the results are slowly but surely getting lost in the general thread.
Basically, I am testing the MHO900 series here, which only differ in terms of bandwidth.
To avoid writing everything again here, here are the links to the corresponding posts.

Arrival and first impressions

Risetime/Samplerate/Intensity Grading

Bandwith Measures via FFT Peak Hold

Fixed Bandwiths 20/250Mhz

Video of the Fan Noise

Hidden Testmode

Update Rate Test

Further tests will follow as long as I have the scope (I don't know how long I'll be able to keep it at the moment).
These will include a repeat and extension of the update rate test.
As well as:
- AWG, signal test
- Bode plot test
- Decoder test
- Noise floor tests
- Anything else that comes to mind
The results will be presented in this thread, including a summary of my impressions of the Rigol.
I can already say that, despite its similarity to the previous models I have tested from the DHO/MHO series, I like it best, considering the price.

To be continued...

Martin

[Martin72]

One last test for today, it's already late here...
Accordingly, I was lazy and controlled the scope from the living room.
The web connection is fast, very good.
Noise level measurement:
One channel (CH1, the others behave in the same way), 1 mV per division, 1 ms per division.
Full bandwidth, 20 MHz, I skipped the 250 MHz.
Then 50 ohm input and 1M ohm.
I consider around 124µV to be good for a 1GHz scope(yes it is...   )   ; at 1M ohm, the level is lower, which is probably an indication that the bandwidth is more limited at 1M ohm—I will test this soon.*
Then I also used Hi-Res Mode, which significantly reduced the level again, but that's no surprise, as the bandwidth drops to 2.5kHz at 16 bits.
Finally, an FFT up to 1Ghz, in the new Averaging Mode (20x).
I discovered something else that wasn't very nice.
At 100ms/div, it's obvious that you can't display an FFT up to 1Ghz or even more – yet you can still enter a “max” span of 2Ghz in the menu.
This shouldn't be possible; “max” should refer to the current FFT sample rate.
I found similar nonsense in the AWG menu, where there are buttons for kHz, MHz- and GHz...
EDIT:
*Those who can read a data sheet have an advantage:
500 MHz bandwidth at 1 MΩ input.

[Fungus]

Finally, an FFT up to 1Ghz, in the new Averaging Mode (20x).

That's a game changer... 

[Martin72]

Yes, for Rigol, that and peak mode are finally the features that Rigol (ALL models) had been missing for a long time.
I can well imagine that these modes will now also benefit other models with the same operating system via firmware update (DHO800, 900, 1000, 4000, MHO2000, 5000).
If not, it would be completely incomprehensible.

[Fungus]

How fast is the pulse from the aux out connector? (rise time)

[egonotto]

Hello,

What is the noise level at 1 V/div?

Kind regards,
egonotto

[Martin72]

Hi,

Here they are, noise at 1V, risetime of Aux out...
Risetime measured with 50 ohm load(input).

[Martin72]

AWG:
I played around with it a little earlier, here are a few comments.
50 MHz is the maximum frequency for this license (very clever of Rigol, by the way), if the waveform is a sine wave, it is 10 MHz for a square wave and 1 MHz for a ramp wave.
The menu is quite straightforward, which corresponds to the sparse feature set.
And then there are a few minor issues in the menu that should be corrected, or rather, a few things are missing.
First, the choice of output impedance:
Hi-Z is clear, but then it doesn't say “50 ohms” like everywhere else on this planet, no, it says “Load”... Great.
This should be corrected.
Then there's the menu for the output level...
The units Vrms, Vpp, and VdBm are missing; instead, there is “kV” as a unit...
This should also be corrected.
There is nothing to complain about in terms of output quality, which is normal standard, with harmonics increasing slightly with rising frequency (FFTs of sine waves).
By the way, you should make sure that the signal is not displayed in full on the screen, as this will cause interference from the ADC due to overdrive.
This is not unusual, but it should be mentioned.
I then left it at 200 mV/div.
Some things in the FFT menu are also a bit confusing, but I'll come back to that later.

[Martin72]

FFT pics...

[ballsystemlord]

I can't wait to have a scope that can do 50Mhz sine wave at 10Kv with it's AWG.
Being able to measure Gdbm without a HV probe will also be cool.

[Hydron]

Please don't, I think a GdBm signal would be a second big bang!

[2N3055]

AWG:
I played around with it a little earlier, here are a few comments.
50 MHz is the maximum frequency for this license (very clever of Rigol, by the way), if the waveform is a sine wave, it is 10 MHz for a square wave and 1 MHz for a ramp wave.
The menu is quite straightforward, which corresponds to the sparse feature set.
And then there are a few minor issues in the menu that should be corrected, or rather, a few things are missing.
First, the choice of output impedance:
Hi-Z is clear, but then it doesn't say “50 ohms” like everywhere else on this planet, no, it says “Load”... Great.
This should be corrected.
Then there's the menu for the output level...
The units Vrms, Vpp, and VdBm are missing; instead, there is “kV” as a unit...
This should also be corrected.
There is nothing to complain about in terms of output quality, which is normal standard, with harmonics increasing slightly with rising frequency (FFTs of sine waves).
By the way, you should make sure that the signal is not displayed in full on the screen, as this will cause interference from the ADC due to overdrive.
This is not unusual, but it should be mentioned.
I then left it at 200 mV/div.
Some things in the FFT menu are also a bit confusing, but I'll come back to that later.

Equally nonsense values for siggen output are µV and nV...

[rusoaie]

One last test for today, it's already late here...
Accordingly, I was lazy and controlled the scope from the living room.
The web connection is fast, very good.
Noise level measurement:
One channel (CH1, the others behave in the same way), 1 mV per division, 1 ms per division.
Full bandwidth, 20 MHz, I skipped the 250 MHz.
Then 50 ohm input and 1M ohm.
I consider around 124µV to be good for a 1GHz scope(yes it is...   )   ; at 1M ohm, the level is lower, which is probably an indication that the bandwidth is more limited at 1M ohm—I will test this soon.*
Then I also used Hi-Res Mode, which significantly reduced the level again, but that's no surprise, as the bandwidth drops to 2.5kHz at 16 bits.
Finally, an FFT up to 1Ghz, in the new Averaging Mode (20x).
I discovered something else that wasn't very nice.
At 100ms/div, it's obvious that you can't display an FFT up to 1Ghz or even more – yet you can still enter a “max” span of 2Ghz in the menu.
This shouldn't be possible; “max” should refer to the current FFT sample rate.
I found similar nonsense in the AWG menu, where there are buttons for kHz, MHz- and GHz...
EDIT:
*Those who can read a data sheet have an advantage:
500 MHz bandwidth at 1 MΩ input.

Hmmm, your "Full bandwidth" noise level is measured at 50MSa/s... careful with the "Auto" settings 

[2N3055]

One last test for today, it's already late here...
Accordingly, I was lazy and controlled the scope from the living room.
The web connection is fast, very good.
Noise level measurement:
One channel (CH1, the others behave in the same way), 1 mV per division, 1 ms per division.
Full bandwidth, 20 MHz, I skipped the 250 MHz.
Then 50 ohm input and 1M ohm.
I consider around 124µV to be good for a 1GHz scope(yes it is...   )   ; at 1M ohm, the level is lower, which is probably an indication that the bandwidth is more limited at 1M ohm—I will test this soon.*
Then I also used Hi-Res Mode, which significantly reduced the level again, but that's no surprise, as the bandwidth drops to 2.5kHz at 16 bits.
Finally, an FFT up to 1Ghz, in the new Averaging Mode (20x).
I discovered something else that wasn't very nice.
At 100ms/div, it's obvious that you can't display an FFT up to 1Ghz or even more – yet you can still enter a “max” span of 2Ghz in the menu.
This shouldn't be possible; “max” should refer to the current FFT sample rate.
I found similar nonsense in the AWG menu, where there are buttons for kHz, MHz- and GHz...
EDIT:
*Those who can read a data sheet have an advantage:
500 MHz bandwidth at 1 MΩ input.

Hmmm, your "Full bandwidth" noise level is measured at 50MSa/s... careful with the "Auto" settings 

Measured AC RMS noise levels will be accurate even with undersampling.

[Martin72]

Hmmm, your "Full bandwidth" noise level is measured at 50MSa/s... careful with the "Auto" settings 

Yes, on the one hand, “full bandwidth” was probably the wrong term.
On the other hand, “Auto” is the most common setting, as the scope can determine the optimal settings itself—at 1 ms/div, you are no longer looking at signals beyond 25 MHz (50 MSa/s), but rather significantly below that.
On the other hand, it is then no longer full bandwidth.
I tried manually adjusting the memory to increase the sample rate.
The levels then rise significantly.
@egonotto:
We measured the noise levels once, always using the same settings so we could compare them – do you remember where that was?

[egonotto]

Hello,

as far as I remember:

We usually used 1 ms/div with sufficient memory to get the maximum sampling rate. With the SDS3000X HD, that was 40 MSamples.
Previously, with the Rigol DHO1000, we had provided the input with a 50 Ohm termination (as a short circuit).
At 1 mV/div, this sometimes yields better values.
I would continue to recommend this, although it makes little difference with the SDS3000X HD.
But in general, noise is measured with a short-circuited input.

Best regards,
egonotto

PS: For 1 MOhm measurements, the 50 Ohm short circuit of the input could improve things somewhat. If not, the MHO9 is not so good in terms of noise.

[2N3055]

Hello,

as far as I remember:

We usually used 1 ms/div with sufficient memory to get the maximum sampling rate. With the SDS3000X HD, that was 40 MSamples.
Previously, with the Rigol DHO1000, we had provided the input with a 50 Ohm termination (as a short circuit).
At 1 mV/div, this sometimes yields better values.
I would continue to recommend this, although it makes little difference with the SDS3000X HD.
But in general, noise is measured with a short-circuited input.

Best regards,
egonotto

PS: For 1 MOhm measurements, the 50 Ohm short circuit of the input could improve things somewhat. If not, the MHO9 is not so good in terms of noise.

That is why we DO NOT put shorting cap on input when measuring noise.
Just an shield on input, in form of one of the metallic caps (with no short to center). With 1MΩ or 50Ω.

Shorting input can mask noise sources that are there. When measuring you would not have anything shorted.

[Kleinstein]

With the 1 M input impedance both the open and shorted input can be relevant. When using an 1:1 probe one would be close to a shorted input case as the signal source is usually relatively low impedance (<< 1 M). With an 1:10 probe the input is close to open with some 9 M (and some 10 pF) in series to the input. Here one would still have a little extra capacitance that would be relevant for the higher frequenies.
For low noise cases the 1:1 probe could still be relevant, even though normally rarely used. There are also measurements directly with a BNC cable, that are close to the shorted case.

Because of the input capacitance there may may not be that much difference between the 2 cases when measuring at higher BW or frequency. There may be a difference in the low frequency ( < 100 kHz) range (could be visible in the FFT).

[egonotto]

Hello,

you want to measure the noise of the device and not what else it picks up.
For nanovoltmeters, there are even expensive shorting plugs available to measure noise.
For example, a low-thermal shorting plug for 34420A costs US$ 265.

If you measure the noise of the PicoScope 4262 without a short circuit, do you get the promised 8.5 uV?

Best regards,
egonotto

[2N3055]

Hello,

you want to measure the noise of the device and not what else it picks up.
For nanovoltmeters, there are even expensive shorting plugs available to measure noise.
For example, a low-thermal shorting plug for 34420A costs US$ 265.

If you measure the noise of the PicoScope 4262 without a short circuit, do you get the promised 8.5 uV?

Best regards,
egonotto

That is why you put a shield on BNC but not a short.
Anything that gets coupled in input form inside the scope IS instrument noise.

On occasion we put 50Ω pass trough terminator on input because that is how we would use it in application.
This is how PicoScope 4262 was measured for that 8,5 µV RMS, not with a short. I documented it where I published that number
Without terminator on input it would have more noise and that IS the point.

For pure instrument noise, BNC shielding cap (without shorting pin) and internal 1MΩ and internal 50Ω termination is way to go.
For an instrument that does not have internal 50 Ω, an external 50Ω terminator on input can interpolate what would it be with 50Ω.

If you short the input, that will show too rosy picture for scopes that have a lot of noise pickup in input stages.
It would not make a difference for scopes that have noise sources elsewhere.

[egonotto]

Hello,

Thank you for your reply. How big is the difference between measuring with a shielding cap and measuring with 50 ohms?

But what do you think about the short-circuit plug for nanovoltmeters?

Kind regards,
egonotto

[Hydron]

The use case for nanovoltmeters is to allow you to null out offsets, not to reduce noise (though it would do that to a certain extent too).

I think 50R termination is a reasonable condition for measuring wideband noise on a scope, as any probes used would likely have 50R output Z, or if passive, have enough capacitance to be in that ballpark at higher frequencies anyway.

Low frequency noise is another matter though, maybe worth comparing with and without termination at 1Mohm/20MHz limit

[Martin72]

I repeated yesterday's measurements, except that I closed the input with a BNC cap.
This did not change the measured values, which remain at 280µV/250µV (50R/1M) at 1mV/Div.

[Martin72]

I wonder how Rigol determined the values in the data sheet.
Magnova provided exemplary specifications for their values (all channels active, 1GSa/s each, 5ms/div, open inputs).

[egonotto]

Hello,

among all the data sheets that specify noise, Magnova was the only one that stated how it was measured. I also find it very strange when, for example, it says 154.2 mV. I would then specify 160 mV.

Kind regards,
egonotto