Author Topic: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.  (Read 26642 times)

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Offline Rosendorfer

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Hi Guys

It is my first post so welcome everyone hire...

I'm in situation regarding decision about new scope.. but ..well ..not everyone needs the same one...

I'm mainly analogue audio, stuff guy and I'm looking for jet affordable but quiet and high sensitivity scope with "usable" FFT option.
So there is Hameg HMO1022 with whatever it means "Reference Class" quiet ADC with 1mV/div @ full bandwidth but with just 2000WFMS/S plus Hameg adv.10 bit high precision mode..and FFT at VGA screen
And I almost made my decision on it, well it is rather on expensive side .... but then I have found out on this forum about new Rigiol DS2000, and now I need Your advice...
New Rigol DS2000 comes with "Class Leading"  0,5mV/div and /hire things gets bit blurry as I can't find anything on official Rigol manuals/ but something like 10 (or even 12bit(!!)) "high precision mode"....with nice 800x4800 FFT screen and 50 000WFMS/S.

So my question is if any  of You guys could give me some advice what really can be seen at 10bit mode FFT scope screen at high sensitivity levels..like 1mV/div. I know that high precision mode comes at bandwidth "cost" but at audio frequencies that should be more than OK.
I have made small calculation and this in theory makes possible to "see":
1mV/div x 8 div = 8mV at full screen so with 10 bit ADC we have 8mV/1024=0,0078mV=7,8uV with Hameg and with Rigol 0,5mV/div half of that so about 4uV... OK there is some noise and quantisation errors but still how realistic and "usable/reliable" it can be?

Well I have been looking about this question around, but seems that it is not very popular subject..
So who if not EEVBlog can shine some light at my dilemma..

Rosendorfer
 

Offline PChi

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #1 on: June 19, 2012, 02:06:24 pm »
I am guessing that the 'high precision' modes are just using the 8 bit ADC and relying on oversampling then digitally filtering the result. I guess it depends what the input signal is doing and whether dither is applied to the ADC. Your calculations of resolution assume a 10 bit converter but it probably is just an rather inaccurate 8 bit so not very reliable. The ADC is optimised for bandwidth. I guess that the waveforms per second update rate may or may not reflect on how much of the input data the FFT uses.

I would also add that modern test equipment loves using software to output a pretty picture that isn't always the full truth.

I have some experience of using an old Tektronix TDS 754 Oscilloscope and didn't entirely trust the high resolution mode. I vaguely remember Dave using the high resolution mode on the Agilent and it not being entirely obvious what was going on.
In my opinion the dynamic range of the Oscilloscope high bandwidth ADCs aren't suitable for audio FFT measurements. Unfortunately there is no substitute for a 'Dynamic Signal Analyser' produced by Agilent or SRS with 16 bit ADCs. Or even more expensive Rhode and Scwartz or Audio Precision or something else.

The low cost low bandwidth option is to use a PC Sound Card and something like ARTA software.
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #2 on: June 19, 2012, 04:07:28 pm »
Hi

Thanks for Your input...
As english is not my native language and it seems, that I like to complicate even simple things things, let my rephrase my question to make it hopefully bit more clear.
Well ..... I'm not at idea of substituting AudioPrecision System2 or R&S Audio System with 1500USD scope../ actually how AP2 cost,  as everybody seems to recommend it.... I need to finally check that.. ;) /
There is no denying that usually scopes ADC are 8bit and 10-12 bit high precisions modes are using kind of multi-sampling that comes at expense of speed on so on....
And finally I'm doing  measurements with 24bit  Audio Sound card and I know they can give pretty impressing results.. but with frequencies higher than 30-40kHz they start to just give up, and this is bit low for many situations and requires Laptop PC Software and some additional work around, so it is not convenient for quick measurements..

My question is how actually high precision scope mode works in real life... and specific in FFT , as this is possibly the only tool that can use it effectively, as seeing difference between 8 and 10 bit in time mode on usual scope screen is questionable.. .this is agreed.

OK..lets try these  way...
My trusted old 8bit scope is able to show FFT down to -70dB but pretty big part is noise, so effectively it can be used to -60-65dB .

So going back to the "high precision" ... with 10 bit in theory we should get into -100dB region and with 12bit mode possible at new Rigols, at speeds lower than 5us, as I recently find out, we should be able to reach -110dB  and this starts to be really interesting.../ well of cause if my dB calculations are OK /
But this is theory and I'm looking for real life info on it ....
Question is what can be REALLY seen at FFT's is there any more useful information, as possibly should be, any influence from memory depth, WFMS/S or any other scope parameters ??

So well any of You guys have any first hand experience regarding that nice looking features...from scopes marketing brochures....???
Maybe Dave, could have a deep(!!) look at it with one of his scope reviews...??

Rosendorfer
 

Offline jahonen

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #3 on: June 19, 2012, 04:59:15 pm »
I think it boils down to SFDR specification, spurious free dynamic range. While averaging tricks improve the noise floor, they don't improve nonlinearities or dynamic range. So you can't reliably measure low level distortion using a scope, at least without using some kind of prefiltering.

If you want to measure just low-level signals without need of wide dynamic range, then just get a preamplifier. With such thing, you can see µV-levels with a DSO. Something like 80 dB of low-noise gain works wonders there.

Regards,
Janne
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #4 on: June 19, 2012, 05:21:18 pm »
Hi Jahonen

Actually I'm just trying to find out what is possible/real .....
But well, pre-amplifier with some notch filters have been planed as next step... ;)

But my point is.... from theory all of that 10-12 bit FFT's  on new scopes seems to be pretty interesting, I wonder where is the "problem" that nobody is going in that way.

I just found out /how can I miss that !!! / wonderfull program from dexter2048  Topic: "Using Rigol DS1052E for spectrum analysis" and well it starts to be really interesting.. I can get away from "build in" scope screen and get some really interesting data out of that pretty quick ...

It seems that finally I will have to get my hands on one of Rigol DS4000/2000 scopes and see for myself what is coming out of that...

Rosendorfer
 

Offline Gunb

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #5 on: June 19, 2012, 08:53:36 pm »
Hi,

as far as I know there are two common methods of increasing resolution: ERES and HiRes. First was introduced by LeCroy, second by Tektronix. Both methods are using filter algorithms for calculating a higher resolution.

You should not only consider the wfm/s. This value depends always on the timebase and is usually NOT constant but decreasing.

I obtain the Rigol DS4012 as well as the Hameg HMO2524. You should know, that the number of samples for FFT of the HMO can be adjusted between 2048 and 65535, the DS4000-series from Rigol is fixed to 700pts constantly only. I assume, the DS2000 uses the same no. of samples cause it's a downgraded DS4000.

From my point of view the HMO offers better FFT analysis.

The low cost low bandwidth option is to use a PC Sound Card and something like ARTA software.

Yes, that's what I've done also for audio measurement. I recommend a soundcard with a good SNR.

Kind regards
Gunb
« Last Edit: June 19, 2012, 08:57:27 pm by Gunb »
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #6 on: June 19, 2012, 09:50:02 pm »
Hi Gunb

This is kind of info I was looking for. Thank You ...!!!

Any chances You could send some photos/screens of FFT measurments from Your scope's ..
What is the dB scale of Hameg FFT at normal and high precision mode and what about scope noise...??
Any chance to compare the same with DS4000..???
Well just any info You could share on my dilemma.

Thanks in advance..!!!

Best regards
Rosendorfer   
 

Offline anotherlin

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #7 on: June 19, 2012, 09:52:08 pm »
Hi,

I do have an Hameg HMO0722, it's the 70MHz model. So far, I'm pretty happy with it.
If you have specific questions, I'll be happy to help you. I can run some test for you if you want.

You may want to check :

http://jeelabs.org/2011/12/02/new-oscilloscope/

The guy of the blog bought an HMO, not sure if it's a HMO0722 or a HMO1022 though.
There's also a video review of the HMO1022 on youtube if you search.

Now regarding the 1mv precision, the scope can only display 8mv peak-peak on its screen (it may acquires more than 8mv).

Unless you want to analyze a signal directly from a guitar pickup (a few mV) or microphone, what would be the point ? A "line signal" would be around 1V, right ?

I'm no expert in signal processing, but for a FFT you're more interested in the frequency content rather than amplitude ?


Best regards,
"Lots of people have made $100K or more mistakes and didn't get the boot. It's called training, why fire them after such an expensive lesson?" -- EEVblog Electronics Community Forum
 

Offline EEVblog

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #8 on: June 19, 2012, 10:34:55 pm »
If you want to measure just low-level signals without need of wide dynamic range, then just get a preamplifier. With such thing, you can see µV-levels with a DSO. Something like 80 dB of low-noise gain works wonders there.

What commercial ones are there?
I've been thinking of rolling my own.
Have used a Tek ADA400 in the past, but not really aware of any others.

Dave.
 

Offline jahonen

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #9 on: June 20, 2012, 09:34:40 am »
If you want to measure just low-level signals without need of wide dynamic range, then just get a preamplifier. With such thing, you can see µV-levels with a DSO. Something like 80 dB of low-noise gain works wonders there.

What commercial ones are there?
I've been thinking of rolling my own.
Have used a Tek ADA400 in the past, but not really aware of any others.

Dave.

I can't name any others. But indeed, I have built one (more for AC applications) myself, at work I put it parasitically on one customer project panel, as there were empty space on the panel (actual board was U-shaped) and I needed the preamplifier anyway to characterize the power supply noise so I designed it to fit to the unused space. I knew that first revision is going to be changed anyway so I can remove the preamplifier from subsequent revisions. Not nice outline and capacitors were too big but it got the job done I had to do:



Schematic

I was a bit surprised that it was not actually necessary to put any shielding on top of the PCB (although shown in the schematic), at least in typical lab environment. Probably partly because of heavy ground planes and low-impedance wide traces, surprisingly little noise couples to the PCB, considering the gain.

Residual noise with inputs shorted.

10 µVp-p signal measured with full bandwidth (around 1 MHz).

Output of a 7805 regulator, loaded with a LED and a resistor.

All voltages shown in those screenshots should be divided by 10000, to get input referred values.

Regards,
Janne
 

alm

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #10 on: June 20, 2012, 11:12:20 am »
What commercial ones are there?
I've been thinking of rolling my own.
Have used a Tek ADA400 in the past, but not really aware of any others.
There is the discontinued Tek AM502, which shares the design with the 7A22/5A22N scope plugins, and is essentially the predecessor to the ADA400. It needs a TM500 mainframe, but it is sometimes available on eBay for well under $100. I think it went down to something like 10 uV/div. Bandwidth was 1 MHz, with selectable low and high pass filters. I seem to recall there is also a differential pre-amp available from Preamble Labs, also sold by Lecroy, but I don't recall the noise floor or gain.
 

Offline robrenz

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #11 on: June 20, 2012, 11:51:12 am »
I've been thinking of rolling my own.

Dave.

Dave, please do, I would buy a "Micro pre amp" in a second. I think many others would also.

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #12 on: June 20, 2012, 01:04:04 pm »

I do have an Hameg HMO0722, it's the 70MHz model. So far, I'm pretty happy with it.
If you have specific questions, I'll be happy to help you. I can run some test for you if you want.

You may want to check :

http://jeelabs.org/2011/12/02/new-oscilloscope/

Best regards,

Hi anotherlin

I have gone thought Your Hameg HMO review/impresions and it is absolutely great job, if You ask me..
And again very interesting blog You have there...

As for my  high precisions dilema I would be very interested in few simple tests if you could run on Your very nice Hameg :)

At Hameg HMO manual ther is something they call High precision mode and they claim then scope runs in 10bit mode. In time mode it is probably hard to see if scope runs 8 bit or 10 bit well maybe at HAMEG VGA screen You could see something worth to try, but that probably would need bit special wawe... rather not simple sine .. but again 8 bit or 10 bit mode  should in theory be pretty nice reflected on FFT screens.
So if You can run some simple sinwawe out of Your lets say CD player.. :), You can burn it on CD ...:)  or from Sound Card possibly in "decent" laptop ...about 10 kHz and maybe second at 20kHz and made FFT analysis of that sine in normal mode and in high precision mode with markers activated in dBV not in VRMS and positioned at top and bottom of the screen so we could see scope claimed dB range and share with us the screens of that that, I'm very interested if there is any new valuable information or not.
If You could go one step further.. :) Very interesting would be to have simple VR resistor about 25-50kOhm set up between CD or Sound Card and scope input and in that way change signall amplitude and try to go pretty low. Lets say if You could do tests with 200mV/div; 20mv/div and 2mV/div and even try to get to 1mV/div and then we possibly could see the scope noise at FFT screen start to get into the picture... Important is to do not change the signal level at CD or sound card but leave that fixed at some standard usually about  2-3 Vp-p and do the changes at VR.
Well last thing is that with tests it is important to run signal in "full scale" on the scope, means that measured sine should have full screen amplitude typically 8div, but not more, so we are using full range of ADC...
Hope it is OK.. And You could find some time to run that tests ...
In any questions please let ma know...
Well and of cause if other knowledgeable guys hire do have some other ideas or see faults in that tests please let us know..

Best Regards
Rosendorfer


 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #13 on: June 20, 2012, 01:45:09 pm »
@ jahonen

Regarding Active Probe with Gain Project let me put my 2 cents.... as I have been thinking about it already...
It should aim at possibly 20MHz bandwidth and LiPo battery powered ..;).
I wonder about 40dB, 60dB, 80dB gain, probably not variable but different probes...
Well just my 2 cents...
But agreed it is pretty interesting project...
 ;D.... Specially for Agilent DSOX2000 owners... Sorry guys, but I just could not resist..;)  8)..

!!! Rigol wfm viewer program from dexter2048 .. it is absolutely amazing toy....!!!....

Rosendorfer

 

Offline anotherlin

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #14 on: June 20, 2012, 03:59:12 pm »
I have gone thought Your Hameg HMO review/impresions and it is absolutely great job, if You ask me..
And again very interesting blog You have there...

jeelabs.org is not my blog. It is the blog of some guy in netherland.

Regarding the precision of the ADC for full scale and lowest voltage, keep in mind that it may not operate at the same voltage as input :

For a mV, signal from probes may be amplified by a preamp before going to ADC.
And for a full scale (10V per division), the input may go through an attenuator before ADC.

So it's not just a question about the ADC precision, but the full system.

For testing, my signal generator is not working currently. However I should be able to do a capture of a low-level signal with my guitar. I'll do that tonight, after work.
"Lots of people have made $100K or more mistakes and didn't get the boot. It's called training, why fire them after such an expensive lesson?" -- EEVblog Electronics Community Forum
 

alm

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #15 on: June 20, 2012, 06:45:53 pm »
Remember that thermal noise is proportional with the square root of the bandwidth, so higher bandwidth means more noise. For 20 MHz of bandwidth and 1 Mohm input impedance, Johnson noise would be about 0.5 mV. Multiply this by 80 dB of gain and you're in trouble. This is why for example the Tek AM502 or ADA400 have a much more limited bandwidth.
 

Offline DaveW

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #16 on: June 20, 2012, 06:54:35 pm »
Looking through some pictures I took when I got my scope, there is one that might be useful to you. The first photo is a 2mV p-p sin signal being fed into the scope from an HP3325A signal generator. I believe the connection was a straight BNC cable, and I can't remember whether I set the input to be hi Z or 50 ohm. The settings were as default, so no high resolution mode or similar. The second photo is the FFT of this signal, so this should give you some idea of noise floor and low level performance
 
I'm part way through moving, so I don't have access to the scope at the moment, but if haven't had any luck in a couple of weeks, I'll get it set up and run some tests for you!



 

Offline larry42

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #17 on: June 20, 2012, 10:22:59 pm »
Hi, I'm afriad I dont have time to really read the whole thread - but I recently needed to do some measurements using my HMO 1524.

Using 1:20 diff probe (you know the cheapo 25MHz type), I was able to confirm that a signal was attenuated down to -70dBm.

A client was amazed that I was basically using this ultra-compact scope as a spectrum analyzer.

I can easily measure down to -90dBm with this scope - I dont have enough attenuation at the moment to measure lower. The peaks of the noise - the noise floor looks to be around -105dBm or so (Peak detect off, HR on, no averaging). If you average, say 8 times, then I see the noise floor down at -120dBm

There is a bit of 1/f noise, and a spur at 10kHz (not sure if internal or external - it's at -97dBm)

The SFDR is not great though - I was doing some MTPR testing, and couldn't get better than about 40-50dB MTPR when I looked at the multitone spectrum on the scope (the sig gen was > 60dB MTPR)

My old work has some DSOX3000 series - they are faster in terms of UI and much faster waveforms/s* etc - but I think that the HMO is great value for money - especially as i got mine with the serial decode options. I was considering a Rigol briefly. But I wanted to support Hameg, for what I think is a unique product.

PS the HMO is *really* quiet acoustically.


*unless you are doing digital, I don't think that wfms/s is that important. 
« Last Edit: June 20, 2012, 10:30:04 pm by larry42 »
If you have an animated GIF in your avatar or signature then I reserve the right to think you're a dolt.
 

Offline Gunb

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #18 on: June 21, 2012, 07:36:20 am »
Looking through some pictures I took when I got my scope, there is one that might be useful to you. The first photo is a 2mV p-p sin signal being fed into the scope from an HP3325A signal generator.

As far as I can see you've set the scope to "Veff". It should be considered, that you get quite another trace if switching to "dBm", which is used usually on most analyzers. Then the noise floor becomes higher.

My old work has some DSOX3000 series - they are faster in terms of UI and much faster waveforms/s* etc - but I think that the HMO is great value for money - especially as i got mine with the serial decode options. I was considering a Rigol briefly. But I wanted to support Hameg, for what I think is a unique product.

PS the HMO is *really* quiet acoustically.


*unless you are doing digital, I don't think that wfms/s is that important. 


I agree with you concerning the HMO. Related to the Rigol DS series I've done a few tests yesterday and I come to the conclusion that Hameg offers much more features for measuring the spectrum. The HMO offers dBV, dBm and Veff for the amplitude, the user can also setup the number of samples for the FFT calculation, the Rigol doesn't. With the HMO you can choose between mode "Normal", "Envelope" and "Average" and with search functionality you can jump automatically from peak to peak. I find that the whole adjustment of the range of the part of the signal to be measured is much more comfortable than on the Rigol.

Most of these features are not offered by Rigol. I've found on a server that they use 700 samples for FFT constantly - that's not much and leads more to an approximate spectrum without the option to go into more details.

Besides I'm not sure if a scope is the right tool analyzing an audio spectrum. Signals in the range of a few kHz lead usually to slower timebases and that delays the update rate of the spectrum. Of course, it can be done, but when I look at special PC applications they might be faster and better suited for audio purposes.


Kind regards
Gunb
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #19 on: June 22, 2012, 12:29:20 am »

Looking through some pictures I took when I got my scope, there is one that might be useful to you. The first photo is a 2mV p-p sin signal being fed into the scope from an HP3325A signal generator. I believe the connection was a straight BNC cable, and I can't remember whether I set the input to be hi Z or 50 ohm. The settings were as default, so no high resolution mode or similar. The second photo is the FFT of this signal, so this should give you some idea of noise floor and low level performance
 

Hi DaveW

Thanks for the photos, let me just say that Your pictures  makes me envy of that scope   8) ... All I can say is more!!! Please... ;D


The peaks of the noise - the noise floor looks to be around -105dBm or so (Peak detect off, HR on, no averaging). If you average, say 8 times, then I see the noise floor down at -120dBm

There is a bit of 1/f noise, and a spur at 10kHz (not sure if internal or external - it's at -97dBm)

The SFDR is not great though - I was doing some MTPR testing, and couldn't get better than about 40-50dB MTPR when I looked at the multitone spectrum on the scope (the sig gen was > 60dB MTPR)

*unless you are doing digital, I don't think that wfms/s is that important. 


Hi larry42

Thanks for Your input,
Very interesting information and absolutely amazing numbers as for noise floor... being able to see down to -120dB !!! well seems that that is worth to have very close look at ...
Any chances You could post some HR=on , FFT pictures..?? This is still thing I miss... And If You could please show some of SFDR limitation, You have mentioned as that is the thing that start to bother me.
Anyway seems that HAMEG is way to go ....


I agree with you concerning the HMO. Related to the Rigol DS series I've done a few tests yesterday and I come to the conclusion that Hameg offers much more features for measuring the spectrum. The HMO offers dBV, dBm and Veff for the amplitude, the user can also setup the number of samples for the FFT calculation, the Rigol doesn't. With the HMO you can choose between mode "Normal", "Envelope" and "Average" and with search functionality you can jump automatically from peak to peak. I find that the whole adjustment of the range of the part of the signal to be measured is much more comfortable than on the Rigol.

Kind regards
Gunb


Hi Gunb

Thank You for information  ... It looks like "Hameg team" is wining ..again....  ;D

If I just could ask  You to check if DS4000 wfm files can be open with program from dexter2048  Topic: "Using Rigol DS1052E for spectrum analysis"; specialy wfm with Rigol's 12bit mode.. that possibly could be very interesting if we could have access to  "12bit raw scope data", then possibly FFT could be done "externally"..
And of cause I very much would like, if possible, to see some screens comparing Rigol and Hameg FFT's with both HR modes on, that would be absolutely great info....

Once more thanks for Your infos guys !!!

All the best
Rosendorfer
 

Offline larry42

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #20 on: June 23, 2012, 06:14:34 pm »
Hi larry42

Thanks for Your input,
Very interesting information and absolutely amazing numbers as for noise floor... being able to see down to -120dB !!! well seems that that is worth to have very close look at ...
Any chances You could post some HR=on , FFT pictures..?? This is still thing I miss... And If You could please show some of SFDR limitation, You have mentioned as that is the thing that start to bother me.
Anyway seems that HAMEG is way to go ....


To the OP - if you are measuring things involving dynamic range in the audio frequency range then a scope - any scope - is not the way to go. The front-ends are not built to provide more than 50-60dB DR, AFAIK.

You can can oversample and do lots of digital tricks and this works well in theory - as long as your ADC is completely linear. I don't think that the oscilloscope ones are (else, why not offer 14, 16, 24 bit sampling modes ;) ?)

For low cost audio analysis I would recommend some external USB 24bit 192kHz soundcard. The better ones will have >90dB SFDR.




If you have an animated GIF in your avatar or signature then I reserve the right to think you're a dolt.
 

Offline T4P

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #21 on: June 23, 2012, 07:18:30 pm »
my laptop's Realtek ALC269 does 90.9db SFDR ... 16bit 96KHz recording but the playback quality on this laptop is phenomenal by any mark
You've got to really see what's the recording max sampling rate
Even the Creative SoundBlaster X-Fi Elite Pro that is about 89SGD does 114.1 ...
 

Offline anotherlin

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #22 on: June 25, 2012, 08:54:03 am »
Hi Rosendorfer,

I didn't have much time at the end of last week.
But here are some captures of my guitar, which features Suhr passive humbucker.
It is the output through a jack cable, with my scope probe at the other end.

As it is a passive pickup, It can reach only 500mV pp by strumming real hard.
With the volume knob at very low setting, I can go to the mV range (first picture).
You may notice that the signal is noisy. I don't it's due to the HMO.
If you short the probe, noise are much less than 1mV, probably around 0,5mV pp.
When volume is up, noise is not visible (second picture) .

So scope seems to work pretty well. Hope it helps you make your decision.

Best regards,
"Lots of people have made $100K or more mistakes and didn't get the boot. It's called training, why fire them after such an expensive lesson?" -- EEVblog Electronics Community Forum
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #23 on: June 25, 2012, 06:21:17 pm »
Hi Rosendorfer,

But here are some captures of my guitar, which features Suhr passive humbucker.
It is the output through a jack cable, with my scope probe at the other end.

So scope seems to work pretty well. Hope it helps you make your decision.

Best regards,

Hi anotherlin

Thanks for Your pictures...
Well I thing we also can assume that Your guitar sounds really nice. ;D
As pointed hire many times Hameg HMO are extremely!!! good scopes and as the low noise goes they are probably the best, at that price level.

Nobody seems to be willing post anything from Rigol scopes, so I take it as the reason to assume that they are not that good.

But as I've try to point few times, I'm really interested in 10bit mode FFT screens, means that if You could turn in Your Hameg HMO scope-- HighPrecision mode ON  and run FFT measurement would be very nice.

Rosendorfer
 

Offline anotherlin

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #24 on: June 26, 2012, 11:52:33 am »
Nobody seems to be willing post anything from Rigol scopes, so I take it as the reason to assume that they are not that good.

I don't think Rigol scopes are bad, they have good reviews. Seems that people having Rigol scopes may be just busy and don't want to go into comparison with Hameg.

But as I've try to point few times, I'm really interested in 10bit mode FFT screens, means that if You could turn in Your Hameg HMO scope-- HighPrecision mode ON  and run FFT measurement would be very nice.

I'll try to find some time to do you an FFT. Note that you have no control over the number of bits used by the ADC. And as I say before, the ADC is probably just part of the system. For such low-level signal, you may have a preamp before the actual ADC.
"Lots of people have made $100K or more mistakes and didn't get the boot. It's called training, why fire them after such an expensive lesson?" -- EEVblog Electronics Community Forum
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #25 on: June 26, 2012, 04:40:35 pm »
Nobody seems to be willing post anything from Rigol scopes, so I take it as the reason to assume that they are not that good.

I don't think Rigol scopes are bad, they have good reviews. Seems that people having Rigol scopes may be just busy and don't want to go into comparison with Hameg.

But as I've try to point few times, I'm really interested in 10bit mode FFT screens, means that if You could turn in Your Hameg HMO scope-- HighPrecision mode ON  and run FFT measurement would be very nice.

I'll try to find some time to do you an FFT. Note that you have no control over the number of bits used by the ADC. And as I say before, the ADC is probably just part of the system. For such low-level signal, you may have a preamp before the actual ADC.

Hi

Actually, I did not told that Rigol scopes are bad, but that probably(!!) not that good as Hameg HMO as far as low noise  and FFT functionality goes.. ;)..
Anyway bit pity that all Rigoll owners are so busy hire...

I'm keeping my fingers crossed about HighPrecision mode ON  FFT measurement...
Please remember about including some marks in dB, I've write long post about it few days ago.... 8)

Rosendorfer
 

Offline Gunb

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #26 on: June 27, 2012, 09:55:00 am »
Yes, very busied at the moment, no time to do additional setups. Devices not at work, used in my home lab.

As mentioned above, there's no big difference between high resolution on/off. And it's only a calculated higher resolution, not a physical one.
For your audio purposes any soundcard should be a better tool.

You can't get much better results using an ADC which is limited to 8 Bit physically, even not with a 10 Bit filter extension. If you want to do audio measurements
the span is also in issue, besides the time needed for calculation, which is not as fast as if using a PC with special software.

You should also consider that switching to high res mode does not affect the sensitivity of the scope, i.e., as with low res you can choose 1mV at min.

For audio measurements I've installed software and a M-Audio soundcard with a good SNR, easier to handle and in particular suited for the frequency domain up to 20KHz.

Are you from Germany? Then datatec might give you a try to test the HMO. Just call them, that's better than any screenshots. If there's time, I'll to post a screenshot, currently not, sorry for that.


Kind regards
Gunb
 

Offline bernie

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #27 on: July 10, 2012, 09:50:40 pm »
Hi Rosendorfer,

Unsure what measurement you are after in FFT (dBm/dBV/Veff), bandwidth, on what signal. The Hameg does not seem to have a on/off setting for High Precision.  Here's a couple of quick screenshot for a noisy 5mV 2kHz signal. The dBm/div can be turned down to 0.5dBm , but can only inspect the FFT at 5dBm / div

Hope that helps

 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #28 on: July 11, 2012, 03:46:06 pm »
Hi Rosendorfer,

Unsure what measurement you are after in FFT (dBm/dBV/Veff), bandwidth, on what signal. The Hameg does not seem to have a on/off setting for High Precision.  Here's a couple of quick screenshot for a noisy 5mV 2kHz signal. The dBm/div can be turned down to 0.5dBm , but can only inspect the FFT at 5dBm / div

Hope that helps



Hi Bernie

First let me say THANK YOU...!!!!!
Finally after few weeks and tons of posts I have screens of Hameg HMO FFT... ;D ;D

And they are looking extremely promising.....!!!

As we already can see some from Your screens very interesting and surprising numbers... as Hameg HMO FFT is claiming it can see something!! down to 1.56uV or -115dBV ;  uV to dBV seems to be calculated well. pls.check at: http://www.sengpielaudio.com/calculator-volt.htm 
Well that looks very interesting as mater of fact there is even "small problem" these numbers are way too good even for 10bit system.. :o :o  Looks more like 12 bit resolution... :o :o :-X
Well -115dBV ... sounds good enough to measure noise of most power supplies and Power Amps .
Seems that Modern scopes are not just simple 8 bit devices... Would be very interesting to have somebody comment on that... some reality check, pls...

Would be great if You could do test for noise floor of scope itself and see with no signal at all connected what FFT is telling us at 1 and 2 mV/div , test with probe disconnected also would be interesting.

Second test if You please, using some clean signal,  with possibly low noise floor!!! for example sine wave from CD player or Sound Card, sounds like interesting candidate, worth to try ..
It does not have to be done at 1mV/div sensitivity ... Can be at 20, 50 or 100mV or so but is important to use full screen vertical space / 8 divisions / as I described in my previous posts and set up FFT markers with dBV and/or dBm scales so we could see the max signal value and minimum signal above noise floor.....
Relay interested what will come out of that..
Well wonder how about HR mode on/off ..??

Anyway once more thank You for posting Hameg HMO FFT ..screens..!!! :) :)

Regards
Rosendorfer



 

Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #29 on: July 11, 2012, 09:04:18 pm »
Actually the dynamic range is determined by the ADC. Most scopes have an 8 bit ADC which could theoretically yield an FFT range of 48dB (6dB per bit -> 8*6=48). Since most ADCs are noisy, may be clocked by clocks with jitter the effective number of bits (ENOB) will be lower. In worst cases less than 6 bits which would translate in about 36dB. So called high resolution and other averaging methods won't get you more bits of resolution than the ADC has. That doesn't make FFT in a scope totally useless though. Its very handy to check filters and do a quick bandwidth check. Just don't expect a huge dynamic range like a spectrum analyser has.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online ejeffrey

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #30 on: July 11, 2012, 10:55:12 pm »
Quote
So called high resolution and other averaging methods won't get you more bits of resolution than the ADC has.

Sure they will.    The quantization noise of an ideal ADC is about 1/4 LSB spread over the entire nyquist interval.  If you filter and decimate your data, it is just as good as starting with a lower speed, higher resolution ADC.  For example, an ideal 8 bit, 1 GSPS ADC with 10 mV full scale with enough dither has a theoretical noise floor of 0.5 nV/sqrt(Hz).  That is less than the johnson noise of a 50 ohm resistor.  Obviously you can't actually get the implied performance from a real ADC: non-linearity, jitter, and clock feedthrough all limit your useful dynamic range.
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #31 on: July 12, 2012, 01:00:12 pm »
Actually the dynamic range is determined by the ADC. Most scopes have an 8 bit ADC which could theoretically yield an FFT range of 48dB (6dB per bit -> 8*6=48). Since most ADCs are noisy, may be clocked by clocks with jitter the effective number of bits (ENOB) will be lower. In worst cases less than 6 bits which would translate in about 36dB. So called high resolution and other averaging methods won't get you more bits of resolution than the ADC has. That doesn't make FFT in a scope totally useless though. Its very handy to check filters and do a quick bandwidth check. Just don't expect a huge dynamic range like a spectrum analyser has.

Hi Nctnico

Well if I may ....
Seems that You are just telling what have been probably true Years ago with first wave of digitall scopes....
Please check for Yourself if TODAY even with simple cheap 8Bit dac Your claiming 36dB is still true, from what I have seen!!! it is not...

The reason of that tread is to find out if that what You are claiming is still true or it is just history,
and we all can learn something NEW

I keep my fingers crossed that guys with HMO scopes will have some time to do few few simple test and share the results, so we will just see!!!! what is possible TODAY...

Hope that hope for progress is not anything wrong... 8)

Regards
Rosendorfer
 

Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #32 on: July 12, 2012, 01:13:40 pm »
Just imagine you have a comparator which can detect 2 levels and a DC level sitting somewhere. If you want to detect the DC level you'll have to add enough noise so the comparator output on average represents the DC level. This scheme has several sources of errors: the quality of the noise and the offset voltage of the comparator. A modern high speed ADC is a string of comparators each with errors which are barely small enough to make the ADC reach its specifications. You can average (oversample) what you want but the result is still loaded with errors.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline jahonen

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #33 on: July 12, 2012, 01:28:54 pm »
It is important to note that one can always increase the gain and measure smaller and smaller signals. But for dynamic range, it is a bit different situation.

Signal with just one sinusoid is not a good test for dynamic range, better test would be to test with two sinusoids, one with large amplitude and one smaller, how small the smaller can be until it is not reliably identified (e.g. falls below distortion products or noise of larger one)?

Regards,
Janne
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #34 on: July 13, 2012, 04:00:21 pm »
Just imagine you have a comparator which can detect 2 levels and a DC level sitting somewhere. If you want to detect the DC level you'll have to add enough noise so the comparator output on average represents the DC level. This scheme has several sources of errors: the quality of the noise and the offset voltage of the comparator. A modern high speed ADC is a string of comparators each with errors which are barely small enough to make the ADC reach its specifications. You can average (oversample) what you want but the result is still loaded with errors.

Hi

I'm pretty "close to earth" person and like to use something more real than my imagination.
Right now we do have screens from Bernie Hameg HMO FFT's. And while that screens alone are not enough to judge on the subject, there are some very interesting numbers to be seen and as for me that numbers are pretty hard to agree with thing You are telling us hire...
If things are like You are saying.... how Hameg dares to even be able to splash that numbers on its screen ???
I'm not saying that it alone proves everything but it is there... and looks pretty interesting, well definitely not in Your estimated 36dB range.... 8)
I say I like to see more... please.
Hope that Guys with HMO scopes will share more FFT's ...
Well maybe even somebody with access to Rigoll DS4000 would post some.

Regards
Rosendorfer
 

Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #35 on: July 13, 2012, 07:30:43 pm »
My Tek TDS744A also has a so called hi-res mode (10 bit). I set my signal generator to generate a triangle wave and made it fill the screen of the scope (first picture). Then I fed the same signal through a 40dB (100*) attenuator and set the scope to 100* magnification (second picture). Now check the differences. When the signal is magnified 100* you are looking at about 1.33 bits of the ADC. Now try to FFT that. A sine wave won't be so bad but a more complex waveform like a triangle is perfectly suitable to make imperfections visible.

Note that I used the trigger output of the generator to trigger the scope on the 2nd channel so the trigger is the same for both situations.
« Last Edit: July 13, 2012, 07:33:40 pm by nctnico »
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Offline bernie

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #36 on: July 13, 2012, 10:43:25 pm »
As someone else mentioned, I was surprised at the size of the Hameg, but the screen is very clear. For what I need, and the price point the Hameg is very good. I think it's a great scope and happy with the interface and features. The Rigol looks very good, but equivalent options would bump up the price compared to the Hameg. Would be interesting to see the Rigol screenshots/feedback.

I thought this link might be useful  http://www.analog.com/static/imported-files/tutorials/MT-001.pdf

SNR = 6.02N + 1.76dB  , for 10Bit would be 62dB + FFT noise floor 10log10(65536/2) = 62+45 = 107dB

I must admit, I hadn't noticed the HiRes option, it was stuck on the second page of the Acquire menu. It defaults to off,  and the other setting is Auto! The FFT floor seems good to about 80-100dB, but I didn't see a great benefit for the FFT in HiRes. It all depends what the signal is and what you want to measure - eg a periodic signal benefits from averaging in the FFT, SNR, bandwidth, samples, window, freq resolution, include LP filtering  etc etc.

Hope the attached screenshots help

1) No signal attached (SCR00)

40KHz AM modulated with 3KHz, 500mV pk-pk
2) Waveform (SCR72) , averaged FFT 8Bit (SCR77 / 79), averaged FFT 10Bit HiRes (SCR78 / 80)

3) Some 200mV audio out from an iPhone at 8Bit (96/97/98) - anyone guess the tune :)

Bernie
 

Offline KedasProbe

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #37 on: July 15, 2012, 10:31:11 am »
a first video of my HMO1022, simple start (sorry that it isn't sharp)
http://youtu.be/S3CBZLbjtqo

I measured the voltage AC on a 10V DC power supply on 5V/div and then viewed it on 20mv/div.
It seems the step size was 50mV...
What was the total range 8*5V??
This would mean 40/0.05=800  --> 9.6 bits   (10bit <-- range = 10.24div*5V)
8bit, 255*0.05 = 12.75V  or 2.55 div

or am I missing something?

(it is just showing the dots, lines can be confusing)

Edit:
Changing the timebase (after measuring 5V/div)
You get 50mv step at 0.5GSa and below (shows "HR" ), 10bit
You get 100mV step at 1Gsa (shows "HR" ), 9bit
You get 200mv step at 2Gsa (hides "HR" ), 8bit
(strange this is 2 bit  ;) )

If you disable HiRes you get 200mV all the time, 8bit

edit: added bit depth
« Last Edit: July 15, 2012, 01:17:10 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #38 on: July 15, 2012, 11:29:46 am »
Did you adjust the volt/div or magnification (zoom)?
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline KedasProbe

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #39 on: July 15, 2012, 11:36:38 am »
Did you adjust the volt/div or magnification (zoom)?
Volt/div, maybe it isn't clear if you didn't watch the video, I took a single measurement set.
« Last Edit: July 15, 2012, 11:38:48 am by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #40 on: July 15, 2012, 12:06:09 pm »
If you change the volt/div setting the input signal is scaled (divided or multiplied) so the full range of the ADC is used to allow for a signal of 8 divisions in height.
If you set your scope to 20mV/div it means that the 8 bit resolution is used for a range of 160mV (625uV/bit). If you set the scope to 1V/div then the ADC output represents 31.25mV/bit.
« Last Edit: July 15, 2012, 12:11:10 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline KedasProbe

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #41 on: July 15, 2012, 12:44:30 pm »
The measurement does point to 10.2 div instead of 8div.  0.2V*255/5V
edit:
I just did a test (I will make a video later) that shows that it is clipped at just 5.1div on the top and the bottom.
Making it 10.2 div for 8 bit. --> Resolution = 4.0% of V/div (25 steps/div) and in full HiRes 1.0% (100 steps/div)
« Last Edit: July 15, 2012, 01:19:56 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #42 on: July 15, 2012, 01:27:11 pm »
But that still doesn't uncover how much of those extra 2 bits are real information or something that is dreamed up by the scope. Using excess digits doesn't make a measurement more accurate. If a multimeter with 10% accuracy shows 1000mV then the real value can be anything between 900mW and 1100mV.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline tinhead

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #43 on: July 15, 2012, 02:01:33 pm »
But that still doesn't uncover how much of those extra 2 bits are real information or something that is dreamed up by the scope.

there are many detailed information available describing how ADC resolution can be increaed
and what are the traps, e.g.:

http://www.actel.com/documents/Improve_ADC_WP.pdf
http://www.atmel.com/Images/doc8003.pdf
I don't want to be human! I want to see gamma rays, I want to hear X-rays, and I want to smell dark matter ...
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Offline KedasProbe

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #44 on: July 15, 2012, 02:26:48 pm »
But that still doesn't uncover how much of those extra 2 bits are real information or something that is dreamed up by the scope. Using excess digits doesn't make a measurement more accurate. If a multimeter with 10% accuracy shows 1000mV then the real value can be anything between 900mW and 1100mV.
This should help you, the black dots are 9bit the blue ones 10bit (I did moved them up one pixel so they wouldn't cover each other)
Maybe you can check which algorithm fits to calculate the blue ones based on the black ones.
(you will have to zoom in)

Edit attached xls based on csv files
(this is changing 8 to 10 bit after the measurement, so it may work differently on Run)
Edit2:
ReSample2.xls (0.5MB) is with HiRes on and off (8bit vs 10 bit) on the same data both 50MSa.

« Last Edit: July 15, 2012, 06:25:12 pm by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #45 on: July 15, 2012, 07:59:54 pm »
Hi

Can see that KedasProbe is having fun with his new scope...

Having seen HMO FFT's screens I have to say it looks very nice... ;D..

As per KedasProbe request for Rigol screens and to check about nctncio triangle shots,
I have spend some time with my old Rigol DS1052E and run some tests,
so KedasProbe and other HMO owners can see how nice FFT they have... ;D
I hope it will add some practical, real life info to this discussion. 8)
Would be perfect seeing something similar run on HMO scopes.

So There are some Triangles...
My Tek TDS744A also has a so called hi-res mode (10 bit). I set my signal generator to generate a triangle wave and made it fill the screen of the scope (first picture). Then I fed the same signal through a 40dB (100*) attenuator and set the scope to 100* magnification (second picture). Now check the differences. When the signal is magnified 100* you are looking at about 1.33 bits of the ADC. Now try to FFT that. A sine wave won't be so bad but a more complex waveform like a triangle is perfectly suitable to make imperfections visible.

Note that I used the trigger output of the generator to trigger the scope on the 2nd channel so the trigger is the same for both situations.


So there are Triangles @10kHz run from  Siglent SDG1025..
Screens are with Rigol FFT option set for full screen and markers @dBVrms .
First "full screen" Triangle @ 200mV/div that goes about 1,5V p-p.
then just FFT screen at 10kHz/div , so You can see just FFT more clearly.

Then 100 times attenuation that is 15mV @ 2mV/div
And again just FFT screen @ 10kHz/div and second FFT @ 25kHz/div so You can see that there is no distortion or any problems till about 300kHz. Everything looks nice and smooth as expected.
Wonder what is at nctnico screens.?
I went even bit further..
to.. 5mV p-p triangle..and even to..1mV p-p.
That are special shots for guys that are complaining at DS1052E scope noise... ;D
Still all looks nice and smooth ...

So hope it is pretty safe to say that  SFDR  or dynamic range at THE CHIPEST RIGOL scope seems to be at list about 60dB.
And second is that FFT noise floor at THE CHIPEST RIGOL scope is about 108-110dBVrms.
And even with THE CHIPEST RIGOL scope some measurment can be done.. 8)

Hope that it will help a bit.
And again and again and again .... would be perfect seeing something similar run on HMO scopes.
Or actually any other scope.

Rosendorfer
Bit more in second post.
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #46 on: July 15, 2012, 08:33:08 pm »
Hi

I have made few more shots I like to show, hope You will like them.

Again from SDG1025 ;
So there is:
Sine wave Full scale 15mVp-p @ 2mV and just FFT's..
I like to show that as hire You can clearly see the noise floor of FFT.
And also low level sine 2mV p-p @2mV.
And...
Even more lowel level as it just triggers bit better:
Square wave at about 800uV p-p ... Yeas pretty clean 800uV p-p on DS1052E scope...

Now I hope on some more nice  FFT's  from You Guys.

Rosendorfer


 

Online nctnico

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #47 on: July 15, 2012, 09:16:30 pm »
Hi

Can see that KedasProbe is having fun with his new scope...

Having seen HMO FFT's screens I have to say it looks very nice... ;D..

As per KedasProbe request for Rigol screens and to check about nctncio triangle shots,
I have spend some time with my old Rigol DS1052E and run some tests,
so KedasProbe and other HMO owners can see how nice FFT they have... ;D
I hope it will add some practical, real life info to this discussion. 8)
Would be perfect seeing something similar run on HMO scopes.

So There are some Triangles...
My Tek TDS744A also has a so called hi-res mode (10 bit). I set my signal generator to generate a triangle wave and made it fill the screen of the scope (first picture). Then I fed the same signal through a 40dB (100*) attenuator and set the scope to 100* magnification (second picture). Now check the differences. When the signal is magnified 100* you are looking at about 1.33 bits of the ADC. Now try to FFT that. A sine wave won't be so bad but a more complex waveform like a triangle is perfectly suitable to make imperfections visible.

Note that I used the trigger output of the generator to trigger the scope on the 2nd channel so the trigger is the same for both situations.


So there are Triangles @10kHz run from  Siglent SDG1025..
Screens are with Rigol FFT option set for full screen and markers @dBVrms .
First "full screen" Triangle @ 200mV/div that goes about 1,5V p-p.
then just FFT screen at 10kHz/div , so You can see just FFT more clearly.

Then 100 times attenuation that is 15mV @ 2mV/div
And again just FFT screen @ 10kHz/div and second FFT @ 25kHz/div so You can see that there is no distortion or any problems till about 300kHz. Everything looks nice and smooth as expected.
Wonder what is at nctnico screens.?
I went even bit further..
to.. 5mV p-p triangle..and even to..1mV p-p.
That are special shots for guys that are complaining at DS1052E scope noise... ;D
Still all looks nice and smooth ...

So hope it is pretty safe to say that  SFDR  or dynamic range at THE CHIPEST RIGOL scope seems to be at list about 60dB.
And second is that FFT noise floor at THE CHIPEST RIGOL scope is about 108-110dBVrms.
You really need a book on how accuracy affects your measurement results  ;) The scope screen starts at approx -45dbV and ends with approx -110dBV with a noise floor at approx -100dB. The effective range is about 55dBV. You should check whether the harmonics have the expected values.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #48 on: July 16, 2012, 10:20:26 pm »

You really need a book on how accuracy affects your measurement results  ;) The scope screen starts at approx -45dbV and ends with approx -110dBV with a noise floor at approx -100dB. The effective range is about 55dBV. You should check whether the harmonics have the expected values.

Let's see...
So we are not talking about at list 20dB extra from Your 36dB dynamic range of 8 bit ADC but now according to Your "judgment" there are "missing" 5dB..... ;)
But...I have proposition, maybe instead arguing about Rigol DS1052E decibels...
You can actually come back to Your Tek and run some nice FFT's at 8 and 10 bit mode and share results.....
Do not tell, You are going to leave us with impression that Tek TDS744A is that lousy as on Your screens..?? 8)

Rosendorfer



 

Offline PA4TIM

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #49 on: August 18, 2012, 02:02:20 pm »
Maybe it is wise to compare apples with apples. dB itself is rather meaningless.
You are talking dBV, that is 20log and most times using the 1M input ( that, on a Rigol 1192 is dropping like a brick while frequency increases, so harmonics will not be true measurements anymore.

But spectrum analysers ( and my HMO ) can use dBm and 50 ohm. And the 50 ohm input is flat accros the bandwidth.

I have several secteum analysers and I seldom use the FFT of my HMO, not that it is bad but it is light years away in usability compared to a real spectrum analyser.


Rigol DS1102 DC imput impedance
« Last Edit: August 18, 2012, 02:05:27 pm by PA4TIM »
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Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #50 on: August 18, 2012, 05:36:22 pm »
Hi PA4TIM

Well let me say that my intention never have been that scope FFT can "replace" proper SA.

My intention was to find out how good or one may say how bad are FFT's at new modern scopes with HR or High Precision modes, like Hameg HMO's or Rigol's DS2000/DS4000. As not everybody have or really needs, nice SA lying around on his bench.

Simple question: What can be seen on modern HR mode scope FFT's ?

No judgement or comments if it is crap or not, just few simple screens, to show what is possible and where are the limits.

Well actually after few pages of posts, discussion, and attempts that is still open question.

Seems that guys that have the right gear for the job do not find that it is worth to use their time for few simple tests and others seems do not have much but their first scope on their bench and good will.

Anyway, so...what actually You mean by Your HMO being light Years from proper SA...??
Any screens possible..??

Kind regards
Rosendorfer
 

Offline PA4TIM

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #51 on: August 18, 2012, 07:50:46 pm »
It was not my intention to make you think FFT is crap or the scopes.

I think, from your answers, you have no or not much experience with spectrum analysers.

The big difference is a scope uses the time domain and from that sampled info that makes forinstance a sinewave on your screen it uses FFT to transform this info to the frequency domain.

If we take a sinewave, the DAC meaures the whole signal, it determes amplitude and frequency from it. It is only 8 bit or so ( digital knowledge is not my thing but I have build and restored serveral SAs, digital and anlog) so the info of he harmonics, phsase noise, pm, AM, FM ect is all in the amplitude at one point at time x. All those points form a sinewave trace.

It is like standing in a bar and all people shouting at the same time, or a radio that has no tunig, you receive all stations at the same time. Bij filtering ( ears or software) we can extract one station. But tall that data is decoded by a 8 bit ADC so there is not much info in there.

A spectrum analyser can be seen as a normal receiver, you turn it across the frequencybands and you here station after station but never two at the same time. M
So if you want good details you can tune in on a station, switch to narrow filter and only hear the parts of the music that are 1KHz in tone.
The SA has a sweepgenerator that does the tuning for you. You can choose the sweepwidth, you can choose the filter width. You can look at the phasenoise from a -30 dBm 12,5 MHz carrier while that carrier fills your screen. See picture below.


Now the sinewave again. It sweeps and listens at the first harmonic, uses the full capability of the DAD only for this signal, then it sweep on and reaching the second harmonic it uses the full capability of the DAC to measure the second harmonic.

You see the difference ?  8 bit for the whole spectrum or 8 bits only for one tiny bit of spectrum.

There is a " but"  In this. Take two pulses, one at 10 MHz, one at 50 MHz. The happen exact at the same time. They last 10 nS. If they occure just within the sample time of the scope ( not in the dead time) both signals are part of the whole spectrum ( for instance 100MHz (and the attenuated signals outside the bandwidth that still are received) the scope listens too. The software filters transform the signal to frequency and you see the poles growing out of the " grass"  ( noisefloor)
But a SA that sweeps at low speed ( like some digital SAs do) are not at teo frequencys at the same time. You can make such a setup by making the pulse repeatble that the SA sweep speed such that it sees the 10 MHz but every time just misses the 50 MHz.
But this is a very extreme situation that would never happen. All SA's were very expensive precision products with very high quality filtering, ultra lownoise amps and very well engineered so bndwidt, sweeptime, filtering was optimised to be sure these things did not happen.

Since a short time there now are cheaper SA's from Rigol. It would be nice to compare one to a real SA to check the performance.


And that is what you want here. You need FFT screenshots from a known signal ( amplitude, phaseniose, harmonics ect) and then compared to the screenshots from a Agilent, Tek, HP or R&S spectrum analyser. Then you can make conclusions.
I can hook up a generator to my Hameg but the screen shot will tell you nothing. You need a reference. I have seen screenshots from the Rigol with intermodulation and strange bumps in th trace but the owner does not have enough knowledge to see if it is a measurement mistake, a bad genertor, overdriving the input amp or just a not to good SA. So the pictures are worthless.
A friend has the Hameg SA and a Tek SA. We compared those and that the Hameg performed very well. My friend is a ex-metrologist who used to work with expensive SAs for a living.

I am now on a short holyday but next week i will make some screenshot compares between FFT and SA for you.

Fred
« Last Edit: August 18, 2012, 07:55:09 pm by PA4TIM »
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Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #52 on: August 20, 2012, 05:12:43 pm »
Hi PA4TIM

That would be more than welcome....

I'm really looking forward to see Your tests...

Kind regards
Rosendorfer
 

Offline PA4TIM

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #53 on: August 21, 2012, 03:00:48 pm »
http://www.pa4tim.nl/?p=2815 Here the results of FFT tests in normal and hires mode compared to a HP 5885B SA.


Look at the amplitude and low noise signal, no averaging, tricks or filters, just pushed the autobutton and used the 50 ohm input.-40dBm at 10MHz.


No difference between Hires and normal.
(see site)

Normal mode, hanning, 32Kpts

Hires mode, hanning, 32Kpts
But, who to trust ? I noticed this later and the HP could not show all harmonics at the same time. So FFT on the hameg has a plus in this field (but see the comment on my site, FFT can in most cases not replace a SA)

A-10dBm signal so the SA can show all at once

Normal mode, 32Kpts, hanning
Harmonics:  -70.26, -60, -84, -71, -78, -89, -85
deviation:             0,    +9    -8    +5   +2  -7    -1


HiRes mode, 32Kpts, hanning
Harmonics: -66.4,  -60,  -75, – 75, -82, -81, -78
deviation:      +3.6   +9     +1    +1    -2    +1   +6
Looks better at the higher harmonics


No difference between modes

Looks the same but instead of around 4MHz/div it is here 5KHz/div. The SA rules  ;)

The Agilent trick, (but they used larger amplitude difference, but could not get both signals synced because the pulser had no inputsync.
 
Analog scopes can do this too. (and a lot more easy to trigger)
www.pa4tim.nl my collection measurement gear and experiments Also lots of info about network analyse
www.schneiderelectronicsrepair.nl  repair of test and calibration equipment
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Offline Rosendorfer

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Re: FFT @ high precision mode with HAMEG HMO vs Rigol DS2000 scopes.
« Reply #54 on: August 22, 2012, 01:08:13 pm »
Dear PA4TIM

What can I say, it is absolutely great work You have been kind to share with us...

And second thing that comes to me is that Your Hameg HMO3522 is /just as R&S scope supposed to be /  "Scope of the Art" ... Measurements capability and resolving power of that machine is just amazing.
For myself having Rigol1052E that what Your Hameg can do and clearly show at FFT's is almost "wonders"....

I have to reconsider few things as seems, that what HMO is showing at "normal" FFT is, as far as I know, "bit more" that should in theory be possible in "normal" 8 bit mode.
Well clearly  that what Hameg can show even at "Normal" mode is way(!) above that what small Rigol can possibly show.

Any way to try find out, if whenever (!) FFT is used, HMO turns some kind of special/extra FFT's HR mode.
That possibly could "explain" extremely high resolving power of HMO FFT's at any "mode". And olso could bit explain "lack of expected" major differences between normal and HR FFT mode.
But just a fought... But well..as for me HMO FFT's at any mode is HR..!!!

Thanks again for taking Your time to share Your measurements with us.....

Rosendorfer



 


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