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DSOX1204G 200Mhz vs Used MSO3014A (Calibrated in 2018)

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kcbrown:

--- Quote from: bdunham7 on October 28, 2021, 05:02:22 am ---
--- Quote from: kcbrown on October 27, 2021, 10:47:46 pm ---The Siglent 2000X+ scope is an incredible scope for its price range.  But good as it is, there's no way it can match a Keysight 3000 series scope except perhaps for noise floor.  This shouldn't be a surprise, seeing how the Keysight is nearly 4 times the price without serial decoding, and 5 times the price with it.

--- End quote ---

200X the memory.

--- End quote ---

Yeah, there is that.  I have to wonder how much of a difference that makes in the analog domain.  Guess it just depends on the problem you're attempting to diagnose.  For digital, having tons of memory is incredibly useful, especially when it's automatically segmented the way the Siglent does it.  Either way, though, the real question is whether or not the advantages of the 2000X+ over the Keysight outweigh the disadvantages, and that's obviously going to depend on the use cases.  A million points isn't all that large these days, but that's only in comparison with other scopes.  Considered by itself, a million points isn't terrible.  You can do a lot with it.

But if digital is what his focus would be, then the Keysight could well be the wrong scope anyway because the MSO option is what would really make the difference for anything other than serial decoding (and even if you're doing serial decoding, having the MSO option is useful for freeing up your analog channels for other things).

2N3055:
Memory is not the problem.
Problem is that you have 4GS/s that is not 4GS anymore as soon as you use any timebase longer than 50us/div. And then drops rapidly. If you set timebase for 2ms/div (to look at somethin 20 ms long) it takes nosedive to 40MS/s..  At that timebase, if you have anything higher than 20 MHz in signal it will alias and show weird artefacts in signal that aren't there.

If you want to look at PSU startup, at say 10ms/div (for 100ms total) you will basically have 20MS/s sampling rate that will make it a 10 MHz oscilloscope without antialiasing filter on the input..
If you want to look at 10 MHz oscillator startup for first 200ms you literally cannot do that. See attachments..

That memory advantage combined with 500uV/div sensitivity and low noise (compared to 4 mV/div on 3000A) makes SDS2000X+ actually much more capable for slow, low level stuff.

OTOH, Rigol MSOX5000, has similar sensitivity and noise as Keysight  all while having 4 Math channels and 4 decode channels, and tons of memory too.. Also, quite fast retrigger rate.

I would look at least at those two just to make sure to understand what can be had for the 1000-1500 USD, new and with warranty.

kcbrown:

--- Quote from: 2N3055 on October 28, 2021, 09:19:31 am ---Memory is not the problem.
Problem is that you have 4GS/s that is not 4GS anymore as soon as you use any timebase longer than 50us/div. And then drops rapidly. If you set timebase for 2ms/div (to look at somethin 20 ms long) it takes nosedive to 40MS/s..  At that timebase, if you have anything higher than 20 MHz in signal it will alias and show weird artefacts in signal that aren't there.

--- End quote ---

Well, seeing how the actual sample rate ultimately determines the maximum frequency you can reconstruct anyway, wouldn't they use a low-pass filter with a variable upper frequency on the input in order to eliminate the aliasing you're talking about?  I mean, this is an issue you'd have even on the SDS2000X series.  Once you make the timebase long enough you can't maintain the native sample rate.  The additional memory helps, of course, but doesn't eliminate the issue.



--- Quote ---If you want to look at PSU startup, at say 10ms/div (for 100ms total) you will basically have 20MS/s sampling rate that will make it a 10 MHz oscilloscope without antialiasing filter on the input..
If you want to look at 10 MHz oscillator startup for first 200ms you literally cannot do that. See attachments..

--- End quote ---

Yep this is true.

No doubt more memory gets you more flexibility, and this is a good point as to how.  It's really a question of how often you're likely to run into such issues. 



--- Quote ---That memory advantage combined with 500uV/div sensitivity and low noise (compared to 4 mV/div on 3000A) makes SDS2000X+ actually much more capable for slow, low level stuff.

--- End quote ---

Yeah, no doubt.  The SDS2000X+ is really quite an amazing piece of equipment.

If only it had a UI as responsive as the Keysight.    :)

Someone:

--- Quote from: kcbrown on October 28, 2021, 10:21:16 am ---
--- Quote from: 2N3055 on October 28, 2021, 09:19:31 am ---Memory is not the problem.
Problem is that you have 4GS/s that is not 4GS anymore as soon as you use any timebase longer than 50us/div. And then drops rapidly. If you set timebase for 2ms/div (to look at somethin 20 ms long) it takes nosedive to 40MS/s..  At that timebase, if you have anything higher than 20 MHz in signal it will alias and show weird artefacts in signal that aren't there.
--- End quote ---
Well, seeing how the actual sample rate ultimately determines the maximum frequency you can reconstruct anyway, wouldn't they use a low-pass filter with a variable upper frequency on the input in order to eliminate the aliasing you're talking about?  I mean, this is an issue you'd have even on the SDS2000X series.  Once you make the timebase long enough you can't maintain the native sample rate.  The additional memory helps, of course, but doesn't eliminate the issue.
--- End quote ---
Some users who are more familiar with other brands of scopes fear aliasing as its pretty easy to produce. But... its very hard to get the Keysight/Agilent meagzoom scopes to show aliasing artefacts as their front end filtering and decimation "just work" (invisibly and without any controls, prioritising maximum sample rate possible at all times).

2N3055:

--- Quote from: Someone on October 28, 2021, 11:24:44 am ---
--- Quote from: kcbrown on October 28, 2021, 10:21:16 am ---
--- Quote from: 2N3055 on October 28, 2021, 09:19:31 am ---Memory is not the problem.
Problem is that you have 4GS/s that is not 4GS anymore as soon as you use any timebase longer than 50us/div. And then drops rapidly. If you set timebase for 2ms/div (to look at somethin 20 ms long) it takes nosedive to 40MS/s..  At that timebase, if you have anything higher than 20 MHz in signal it will alias and show weird artefacts in signal that aren't there.
--- End quote ---
Well, seeing how the actual sample rate ultimately determines the maximum frequency you can reconstruct anyway, wouldn't they use a low-pass filter with a variable upper frequency on the input in order to eliminate the aliasing you're talking about?  I mean, this is an issue you'd have even on the SDS2000X series.  Once you make the timebase long enough you can't maintain the native sample rate.  The additional memory helps, of course, but doesn't eliminate the issue.
--- End quote ---
Some users who are more familiar with other brands of scopes fear aliasing as its pretty easy to produce. But... its very hard to get the Keysight/Agilent meagzoom scopes to show aliasing artefacts as their front end filtering and decimation "just work" (invisibly and without any controls, prioritising maximum sample rate possible at all times).

--- End quote ---

You are correct, Keysight uses all kinds of neat tricks, and it kinda deals with some aliasing artefacts. For instance it will silently use Peak detect to extract outside envelope of AM modulated signal that should alias. But that will be only screen display, if you press zoom, zoom will show nonsense. But, still, better than others.

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