How to Avoid Oscilloscope Aliasing Pitfalls for Accurate Measurements - Workbench Wednesdays

The Nyquist Theorem says that you must sample a signal at two times its fastest frequency, right? However, even if you do that, aliasing on an oscilloscope can still occur! Aliasing is when a fake signal shows up on the screen due to undersampling of the original signal. Aliasing can happen for several reasons, even on an oscilloscope with enough sample rate.

The most common cause is that the sample rate drops on longer time bases. In this video, learn from James what the REAL theorem says, what aliasing looks like, and how to avoid it in your work.

#0:00 Welcome to Workbench Wednesdays
#0:36 Bald Engineer's Sampling Explainorem
#2:02 Aliasing Examples
#4:16 Why Aliasing Can Happen
#7:06 Sample Rate

#antialiasing #oscilloscope

[Darkipod]

Very good video on aliasing, I feel like most labs in school dont cover this topic appropriately!

[MAYERMAKES]

i recently upgraded my scope, could not trust the old one anymore..it might just have had a to slow sample rate for what I measured. huh. would explain why the error was not rproduceable..it was just off.

[HL]

Is aliasing a practical problem if the analog bandwidth is significantly lower than the signal? E.g. with an analog BW of 50MHz and 500MSa/s? (Signal >250MHz)

[HL]

Is there any chance of something showing as the wrong frequency on a purely analog scope? I saw a 200MHz wave (some ringing) on my 60MHz BW scope. Assuming attenuation like a standard r-c filter I calculated the signal to be ~4ish times larger amplitude in reality than displayed on the screen. How good are the chances of this being correct?

[Clark-Mills]

Random thought... Add randomness / jitter to the sampling slice... eg +/- rnd(5%) and that should help alert to aliasing.