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REVIEW - Rigol DS2072 - First Impressions of the DS2000 series from Rigol
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Carrington:

--- Quote from: Teneyes on July 01, 2013, 08:17:07 pm ---
--- Quote from: Carrington on July 01, 2013, 07:26:24 pm ---Oh no please do not misunderstand me. Respect please. I'm just saying what I think. Owon is not the best, but recognize that in the image above is nothing short, regarding BW.
Please understand that my native language is not English, so may that I am not express properly.

--- End quote ---
@ Carrington
Yes sorry , and I apologize

 To be complete you could say you are comparing :

 A  Rigol     DS2072(hacked)   with 2.0 GSa/s  at  $800  200 Mhz
 A  Owon      SDS9302          with 3.2 Gsa/s  at $1500  300 Mhz
 An Agilent   DSO-X-3502A      with 4.0 GSa/s  at $8000  500 MHz

--- End quote ---

In fact, I took it for granted. Thank for your clarification.  ;)
zibadun:

--- Quote from: marmad on July 01, 2013, 08:14:28 pm ---
zibadun: Man, we've been talking about this for ages already here - it's not about measurement; it's about incorrect display. The point is - you shouldn't see a waveform of a lower frequency - you should see noise (see what the 1MHz waveform SHOULD look like at that time base).

...

Of course there is - Agilent does it. It's actually fairly easy - there are papers written about it (linked in earlier posts in this thread). You just do random decimation from sampled data to display data (e.g. instead of displaying every Nth sample, you vary the decimation). So instead of seeing a FALSE lower frequency, you see NOISE.


--- End quote ---

I saw the "random decimation" note.   You can  prevent aliasing from appearing on the lower resolution image but you can't remove aliases from the sampled waveform if you selected too low sampling rate for your signal. There is simply no data about what was happening in between the samples.  You can't look back and apply some algorithm that will turn aliases into noise and will leave "real" frequencies untouched. 

Here is what I can get this function to do.  Note false paterns removed by  the Antialiasing feature.    Sometimes it has the opposite effect and makes the picture worse. You just have to toggle on and off and use the one that looks better.   Now show me the Agilent 1 Mhz sampled with 200 khz rate and turning it into noise ;)


marmad:

--- Quote from: zibadun on July 01, 2013, 09:39:45 pm ---I saw the "random decimation" note.   You can  prevent aliasing from appearing on the lower resolution image but you can't remove aliases from the sampled waveform if you selected too low sampling rate for your signal. There is simply no data about what was happening in between the samples.  You can't look back and apply some algorithm that will turn aliases into noise and will leave "real" frequencies untouched.
--- End quote ---

I can't believe you're still arguing this point. Anti-aliasing is a proven mathematical formula which works (if implemented correctly). Random decimation is equivalent to stochastic sampling:

"By sampling stochastically, there is no "Nyquist frequency" to talk about, so aliasing will no longer be a problem as before. However, this comes at a price. What you gain in anti-aliasing, you lose by noise in the system. The stochastic sampling introduces high-frequency noise, although for several applications (especially in imaging), aliasing is a much stronger nuisance than noise."

How well does it work? Well, the Agilent X-Series DSOs have anti-aliasing on ALL THE TIME - you can't even turn it off. Now I personally think you should have the ability to switch it off, since it can generate 'lumpy' looking waveforms when zooming in on slightly under-sampled waveforms (caused by the above-mentioned introduction of noise) - but the point is that it works to prevent aliasing. There is no question that it works - but Rigol HAVE NOT IMPLEMENTED IT CORRECTLY!


--- Quote from: zibadun on July 01, 2013, 09:39:45 pm ---Here is what I can get this function to do.  Note false paterns removed by  the Antialiasing feature.    Sometimes it has the opposite effect and makes the picture worse. You just have to toggle on and off and use the one that looks better.
--- End quote ---

Sorry, this is not correctly implemented anti-aliasing. If you think it is, you don't understand the process.
Teneyes:
Here is an effect of the signal input frequency passing through some sort of beating snyc with the a sample rate of at only 4 times the input
The DSO is Sampling at 2MSa/s
Anti-Aliasing ON

Note the input varies from 499.900 KHz to 500.002 KHz  SAwtooth Waveform
note the Frequency Counter in top Right

I find it interesting, and I will watch for it, as an error
I think this shows a fixed sample collection frequency and not a Random one

An excerpt from Agilent
---------------------------------------------------
Random decimation (see References)
Simple decimation (= regular sampling) is the most common decimation technique in
DSO’s and it is exceptionally prone to aliasing. However, the discarded samples can be
used to prevent the display of aliased waveform. The random sample selection prevents
an alias (or beat) frequency from developing by converting low frequency “spurs” to noise.
(For masochists only ? A. V. Balakrishnan: On the Problem of Time Jitter in Sampling,
IRE Trans. on Info. Theory, April 1962.)
With random decimation (= stochastic sampling) the resulting display is a fuzzy band much
like what would be seen on an analog scope.

However, this technique should be turned off for analysis that requires samples at exact regular time intervals.

Edit  UPDATE
  Setting Memory Depth to Auto in Last picture, all Good
g2:
Hello
There is  a new firmware to Rigol DS2000:
DS2000(DSP)update_00.01.01.00.02.
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