Products > Test Equipment
is it true, oscilloscope must reach at least 4x observed freq?
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Someone:

--- Quote from: Fungus on September 14, 2022, 01:32:13 am ---
--- Quote from: Someone on September 14, 2022, 01:11:17 am ---
--- Quote from: The Electrician on September 13, 2022, 03:54:41 am ---Please give us some examples where 2.5x is inadequate.  :)
--- End quote ---
Please provide the band limited signal source that has zero energy above the measurement frequency and I'm sure it would be difficult.
--- End quote ---
I'll take that as a no.
--- Quote from: Someone on September 14, 2022, 01:11:17 am ---Its not some simple every situation works at 2.5x or everything is fine
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No, but in the real world there are some very simple cases that fail below 2.5x. 2.5x is a good starting point.

FWIW: I was observing the AM modulation effect below 2.5x using a hardware reconstruction filter.

--- End quote ---
Again, this can keep going around. You stick with 2.5x as the magic figure yet with none of the other simultaneous conditions/requirements specified or quantified. Complete nonsense. If you want to talk about 2.5x sample rate vs frequency being some accurate or significant number, then you need to work through the rest of the maths that justifies that. "hardware reconstruction filter" says nothing of its form/length/characteristics and is something that is usually undocumented in an oscilloscope.

Observing something which looks "ok" to you, is not quantifying anything. When you are the one being so insistent on 2.5 as some magic quantification. 2.5x is a massive gross simplification that looks ok in most cases for a single frequency sine wave.
Fungus:

--- Quote from: Someone on September 14, 2022, 02:07:51 am ---When you are the one being so insistent on 2.5 as some magic quantification.

--- End quote ---

Me? I'm not the only one. Rigol/Siglent/etc. have been building it into their oscilloscopes for many years and people are happy with the results.

What number would you suggest as a workable compromise for building real devices?
Someone:

--- Quote from: Fungus on September 14, 2022, 02:32:19 am ---
--- Quote from: Someone on September 14, 2022, 02:07:51 am ---When you are the one being so insistent on 2.5 as some magic quantification.
--- End quote ---
Me? I'm not the only one. Rigol/Siglent/etc. have been building it into their oscilloscopes for many years and people are happy with the results.

What number would you suggest as a workable compromise for building real devices?

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As I keep saying, there is no single figure. It depends on what the desired outcome/performance requirement actually is. These things can be quantified and discussed, but instead the shortcut/"rule of thumb" is shouted as some absolute (by you and others) who actually have no understanding of its basis. The short and oversimplified answer is easy to communicate, and is dominating the discussion. While the complex and actual answer is buried by the noise.
BillyO:
Point made.  Too bad.
EEVblog:

--- Quote from: oxy on September 12, 2022, 04:43:14 pm ---some people say, if I wanna observe 100MHz, I must use an oscilloscope that reaches at least 400MHz.

--- End quote ---

Technically not true, but a good rule of thumb. It depends on the front end bandwidth filter shape and the interpolation used. IIRC there is a Tek paper somewhere that goes through the math for x2.4 is the minimum or something for a gausian shape front end.
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