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How much noise floor and other things matter in oscilloscope usability
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Fiorenzo:
So, I did some test, just to learn and experiment.

Same crappy psu, two probes ON in DC mode, one disconnected and the pink one probe on the psu output.
First photo 10x attenuation, second photo 1x.

The ripple of the psu is about 150mv, now the front end noise seem to make a good part of the noise saw on the ripple wave, high resolution or avarage get rid of a big part of this noise. If I did not be aware of the noisy front end i could think that the noise in the ripple was from the psu itself.
Second if i work with the probe in 1x mode the ripple Is now very evident.
Is this the right way to check It? I mean in 1x mode.
Should i use AC or DC mode?
I have read that AC mode get rid of the DC bias so good to work in this way...
Fiorenzo:

--- Quote from: Fungus on December 24, 2021, 10:16:52 pm ---
--- Quote from: Fiorenzo on December 24, 2021, 10:06:26 pm ---Hahahaha you all good guys!
I like you

--- End quote ---

Have you tried averaging mode yet?  :popcorn:

--- End quote ---

Yes many times, and also hi-res mode.
I didn't used It in the photos because i wanted to show the real front end noise.

Actually i really like this rigol, Is a powerfull scope, but i have never put my hands on the siglents
Fungus:

--- Quote from: Fiorenzo on December 24, 2021, 10:19:40 pm ---If I did not be aware of the noisy front end i could think that the noise in the ripple was from the psu itself.

--- End quote ---

Ripple can only be at the switching frequency of the PSU, never in the MHz range.


--- Quote from: Fiorenzo on December 24, 2021, 10:19:40 pm ---Second if i work with the probe in 1x mode the ripple Is now very evident.
Is this the right way to check It? I mean in 1x mode.

--- End quote ---

Yes. 1x mode with 20MHz bandwidth limiter and maximum averaging.


--- Quote from: Fiorenzo on December 24, 2021, 10:19:40 pm ---Should i use AC or DC mode?
I have read that AC mode get rid of the DC bias so good to work in this way...

--- End quote ---

AC will center the ripple waveform around zero so you measure RMS, etc.

(ie. it's good)

Fiorenzo:

--- Quote from: bdunham7 on December 24, 2021, 09:17:11 pm ---
--- Quote from: Fiorenzo on December 24, 2021, 08:20:51 pm ---Here I am, I did the test you asked for, please let me know whath do you think about It.
Thank you very kind!

--- End quote ---

So just as a quick apples-to-apples comparison with your first example, I set up an SDS1104X-E with the same no-probe, 20MHz BW, 5us/div and 1mv/div.  Then I connected a 1mVrms 100kHz signal so you can see the suitability of the scope for viewing such a signal.  The noise makes it a bit jumpy and jittery because it affects the trigger point.  I have some low-frequency noise that isn't from the scope but is from other stuff that I have around that I can't turn off right now, so I did both a live snapshot and a stopped picture, which is effectively a single-shot.  As you can see, the scope is perfectly usable on 1mV signals and your Rigol, which is over 3X as noisy, might have a tough time with the same signal.

I also took a snapshot with the input set to GND, which shows you the ADC noise, or so I think.  The LSB at this setting is 40uV, so the peak-to-peak noise is 1 bit. 

I can't tell you what scope works best for you, but if you work at all with small signals, the front-ends of the entry level Siglents is definitely the best for the buck.  Features like the ERES acquisition mode and the 10-bit mode of the SDS2000X+ series do make them better, but you shouldn't generally count on multi-capture averaging even though it can look very good, as this can lead to errors.

--- End quote ---

Ahhahaah bdunham7 with the same settings i get almost 5 times your noise. The Rigol really like noise....
Fiorenzo:

--- Quote from: Fungus on December 24, 2021, 10:34:17 pm ---
--- Quote from: Fiorenzo on December 24, 2021, 10:19:40 pm ---If I did not be aware of the noisy front end i could think that the noise in the ripple was from the psu itself.

--- End quote ---

Ripple can only be at the switching frequency of the PSU, never in the MHz range.


--- Quote from: Fiorenzo on December 24, 2021, 10:19:40 pm ---Second if i work with the probe in 1x mode the ripple Is now very evident.
Is this the right way to check It? I mean in 1x mode.

--- End quote ---

Yes. 1x mode with 20MHz bandwidth limiter and averaging mode enabled.


--- Quote from: Fiorenzo on December 24, 2021, 10:19:40 pm ---Should i use AC or DC mode?
I have read that AC mode get rid of the DC bias so good to work in this way...

--- End quote ---

AC will center the ripple waveform around zero so you measure RMS, etc.

(ie. it's good)

--- End quote ---

Thank you fungus you are helping me very well.

And also merry Christmas in advance to everyone!!
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