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Oscilloscope probe ground leads act as FM attennea

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ebastler:

--- Quote from: Martin72 on October 25, 2023, 08:07:14 pm ---The case is clear, the disturbance comes from the generator, which catches something...

--- End quote ---

That's even better news! Noise on the 1 kHz reference signal really is irrelevant. As long as the scope input is unaffected and can measure real-world signals with low noise, everything is fine and dandy.  :-+

dmulligan:
I have a LiteOn PSU.  If the noise is coming from the PSU, wouldn't I get the same noise using the ground clip as with the alligator lead?  The PSU is on the floor and my scope is on my desk.  I will move it to yet another room soon.

I knew to expect extra noise on a DSO especially a higher BW scope, this is more than I expected.  The frequency and amplitude of the noise looks random.

Although the frequency looks to be random, perhaps it isn't.  If I am using FFT correctly, the only peak that sticks out above harmonics of the original signal is 63.0 kHz.

David Hess:

--- Quote from: dmulligan on October 25, 2023, 10:17:59 pm ---I knew to expect extra noise on a DSO especially a higher BW scope, this is more than I expected.  The frequency and amplitude of the noise looks random.
--- End quote ---

It looks pretty normal to me for a 100 MHz bandwidth when using the ground clip and the built in calibration signal.  My 300 MHz DSO would look even noisier.  If I use a probe tip to BNC adapter to connect directly to a BNC, then the calibration signal is clean. (1)

(1) Some old Tektronix oscilloscopes used a BNC for the calibration signal, so this can be done on the oscilloscope itself but a function generator output works just as well for calibration.

Martin72:

--- Quote ---this is more than I expected. 
--- End quote ---

Once again, and as far as I'm concerned for the last time, you're worrying about this unnecessarily.

dmulligan:
My #1 concern was that I don't have a dud scope.  I didn't feel any better about that having seen Fungus' and Martin72's relatively clean waveforms didn't make me feel any better. 

I tried moving the scope around to different parts of my house and my 3rd location produced much better results.  So the problem is environmental.  I am not really surprised as I am 100M from a transmission line and there is so much computer and electronics gear around my desk. 

Thank you all for helping alleviate my fears.  Now I need to figure out what I can do to use my ground alligator leads at least sometimes and, more importantly, learn how to use this little thing.

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