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Why do oscilloscopes have bandwidth limits?

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Anding:

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I'll do it in one....

"Do you want to pay for it?"

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That is a financial constraint.  What is the necessary physics that one needs to pay for?

Brumby:
There is a reason electronics in the RF region is often referred to a voodoo.

I know enough about the subject to know I understand extremely little - just a few principles and almost and next to no practical experience.  I've tuned 27MHz mobile antennae and not much else.

Someone:

--- Quote from: Anding on November 02, 2022, 10:05:13 am ---
--- Quote from: Fungus on November 02, 2022, 09:28:48 am ---Why can't my car go faster than sound?
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No reason why it shouldn't but that would require an engine sufficiently powerful to accelerate the car against the restive forces of friction and air resistance which increase with velocity (reference Newton II: F=ma), and sufficient fuel onboard (mass which itself needs to be accelerated) to complete the acceleration.  In the case of a car, it would require rolling gear that maintains it's mechanical integrity at the high RPM for travel above 330 m/s.

Can you put the equivalent physics for a 'scope in two sentences?
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Same as the car needing more power and expensive fancy wheels/tires, fast amplifiers need more power and expensive components. Jamming in more power needs all the supporting expense or it blows up.

Anding:

--- Quote from: Brumby on November 02, 2022, 10:25:10 am ---There is a reason electronics in the RF region is often referred to a voodoo.

I know enough about the subject to know I understand extremely little - just a few principles and almost and next to no practical experience.  I've tuned 27MHz mobile antennae and not much else.

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Yes, this is bringing back memories of simulating RF circuits with a package called "Super Compact" many years ago (I was just running the scripts and printing out the logs ;-) .  Answering my own question here but

The lumped circuit abstraction model starts to break down at RF frequencies and we can no longer treat components as discreet.  The circuit board itself has to be modelled.  At the same time as an oscilloscope is a measurement tool, a specification has to be given over which it maintains linearity of response and for which calibration is accurate.  A convenient way to do that is to _impose_ (I'm guessing here) a low bandpass filter on the front end to exclude the region which the maker has not designed for (price point of the design considered)

I'm curious, with ingenuity what use can be gotten "above the bandwidth limit".  This can be experimented using a simple FPGA to generate fast (200MHz) clocks and waveforms.  Ok there's a project!

Anding:

--- Quote ---fast amplifiers need more power and expensive components

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That is very helpful thank you

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