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is it true, oscilloscope must reach at least 4x observed freq?
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Fungus:

--- Quote from: robert.rozee on September 13, 2022, 11:38:08 am ---just for a laugh, why don't we bring in some empirical data? a novel approach, i must confess, but do humour me just for a moment.

980Hz signal (approx) of about 8v p-p. sampled at various sampling rates:

--- End quote ---

That's not a 980Hz signal.

That's a 980Hz signal plus a 2940Hz signal plus a 4900Hz signal plus a 6860Hz signal plus ... etc.

The whole "Nyquist" thing only works when the signal is bandwidth limited.

Ref: https://en.wikipedia.org/wiki/Square_wave
robert.rozee:

--- Quote from: Fungus on September 13, 2022, 11:49:26 am ---That's not a 980Hz signal.
That's a 980Hz signal plus a 2940Hz signal plus a 4900Hz signal plus a 6860Hz signal plus ... etc.
The whole "Nyquist" thing only works when the signal is bandwidth limited.
Ref: https://en.wikipedia.org/wiki/Square_wave

--- End quote ---

piffle!   :scared:

it is a 980Hz square wave, and a perfectly acceptable example of what an oscilloscope is used for measuring. if the only thing you are going to measure is sine waves, then why even bother with an oscilloscope? get a frequency counter and RF voltmeter instead    :palm:


cheers,
rob    :-DD
Fungus:

--- Quote from: robert.rozee on September 13, 2022, 12:01:13 pm ---it is a 980Hz square wave, and a perfectly acceptable example of what an oscilloscope is used for measuring.

--- End quote ---

Sure, but as you demonstrated so visually: It's not something you can sample and reconstruct with a 2kHz sampling system.

Because... it's a 980Hz sine wave plus a 2940Hz sine wave plus a 4900Hz sine wave plus a 6860Hz sine wave ... to infinity.

robert.rozee:

--- Quote from: Fungus on September 13, 2022, 12:17:41 pm ---... to infinity.

--- End quote ---

the device generating the square wave did not make use of an form of infinity, either theoretical or actual.

now a square wave can be represented by an infinite sum of sine waves, but it is not made out of them. it is made with just a little fellow switching a light switch: on... off... on... off... on... off... very fast.

the infinite sum of sine waves you talk about only exists in one's imagination.


cheers,
rob   :-)
Fungus:

--- Quote from: robert.rozee on September 13, 2022, 12:38:12 pm ---the infinite sum of sine waves you talk about only exists in one's imagination.

--- End quote ---

Fun fact: Your ears can't tell the difference between a 10kHz square wave, a 10kHz sawtooth wave and a 10kHz sine wave. They all sound exactly the same!

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