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How much noise floor and other things matter in oscilloscope usability
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Fungus:

--- Quote from: Fiorenzo on December 23, 2021, 03:24:21 pm ---Ok, you all are giving me many usefull information, but now give a look to the attached photos.
The first image shows the apparent noise of CH1, It is set in AC mode, 1X attenuation, without bandwith limit

--- End quote ---

Never use 1x mode without the bandwidth limit.



nb. 10x mode is what you should be using almost all the time. 1x mode is only for very special cases.
Fungus:

--- Quote from: Fiorenzo on December 23, 2021, 03:36:01 pm ---What circuits works with such a low signal?  This is my question from the beginning.

--- End quote ---

The example that's usually given is "power supply ripple", but unless you're designing a switched mode power supply then you probably don't need that.


--- Quote from: nctnico on December 23, 2021, 03:15:51 pm ---Yes, and thick traces just suck. Try to make a cursor measurement on a trace that is 20% of a division even with V/div set to 1V/div. Needless to say that small variations of a signal are also lost in a noisy oscilloscope.

--- End quote ---

Put it in the middle of the trace.

Oscilloscopes aren't that accurate anyway - only about 5% even on a low-noise oscilloscope.

Edit: You can also turn on color gradient mode and the true signal will be highlighted for you.  ::)



(I just learned that trick from the video below and you can be sure it will be repeated in all future "Rigol noise" threads...  >:D )
Fungus:
If the signal you're looking at is periodic (repeatiing) then you can turn on hires mode and look at the average of multiple waveforms:


egonotto:

--- Quote from: nctnico on December 23, 2021, 02:53:04 pm ---
--- Quote from: Fungus on December 23, 2021, 02:51:59 pm ---
--- Quote from: Fiorenzo on December 23, 2021, 12:00:05 pm ---For example the noise floor:
In what situation really matter to have an oscilloscope with a "low" noise floor?

--- End quote ---
When you're measuring very small signals.

--- End quote ---
Actually not because the relative noise floor remains more or less constant!
I just tried on an R&S RTM3004. At 1V/div I get 17mV stdev. At 10V/div I get 170mv stdev (Stdev= RMS with DC removed). The noise floor scales with the V/div setting.

--- End quote ---

Hello,
this is much better than on RTA4004. R&S says: (50 Ohm 1GHz)
1 V/div  31.4 mV

Best regards
egonotto
nctnico:

--- Quote from: egonotto on December 23, 2021, 07:39:53 pm ---
--- Quote from: nctnico on December 23, 2021, 02:53:04 pm ---
--- Quote from: Fungus on December 23, 2021, 02:51:59 pm ---
--- Quote from: Fiorenzo on December 23, 2021, 12:00:05 pm ---For example the noise floor:
In what situation really matter to have an oscilloscope with a "low" noise floor?

--- End quote ---
When you're measuring very small signals.

--- End quote ---
Actually not because the relative noise floor remains more or less constant!
I just tried on an R&S RTM3004. At 1V/div I get 17mV stdev. At 10V/div I get 170mv stdev (Stdev= RMS with DC removed). The noise floor scales with the V/div setting.

--- End quote ---

Hello,
this is much better than on RTA4004. R&S says: (50 Ohm 1GHz)
1 V/div  31.4 mV

--- End quote ---
I switched the 20MHz bandwidth limit on in order to allow making comparisons with other scopes. The example is just to show that the noise floor scales with the V/div setting.
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