Electronics > Beginners

O-Scope - Capturing the correct/full signal

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logictom:
You've lost me there.
The sample rate goes up when you decrease the time scale? So I get 100M samples at 2ns but fewer at 100ms? Hence why it takes longer to show the signal at 500ms? Surely I should see the effect more so at a 100µs than at 20ms then?

TopherTheME:

--- Quote from: allanw on October 10, 2010, 08:55:54 pm ---It's aliasing. When you sample a signal with frequency f, you need to sample it at at least 2 times the frequency or else you'll get a false image of the signal

--- End quote ---

Given the time base and frequency of the signal he is sampling, I would never have guessed this. After you mentioned it I noticed that the sampling rate isn't displayed on the screen. Is this just a Rigol thing? Most modern DSOs I've used tell you the sample rate in the corner of the screen so you know if you have to worry about aliasing.

logictom:

--- Quote from: TopherTheME on October 10, 2010, 10:26:31 pm ---
--- Quote from: allanw on October 10, 2010, 08:55:54 pm ---It's aliasing. When you sample a signal with frequency f, you need to sample it at at least 2 times the frequency or else you'll get a false image of the signal

--- End quote ---

Given the time base and frequency of the signal he is sampling, I would never have guessed this. After you mentioned it I noticed that the sampling rate isn't displayed on the screen. Is this just a Rigol thing? Most modern DSOs I've used tell you the sample rate in the corner of the screen so you know if you have to worry about aliasing.

--- End quote ---
It is shown on one menu, at 100µs it samples at 2.5M whilst at 20ms it samples at 10k.
Edit - Dual mode, doubled for single.
Just in case anyone is interested:

PeterG:
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Regards

Simon:
yea we have established that it is a moderator permissions issue that maybe chris can fix as he has more powers that myself and geoff