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When I hold my oscilloscope probe and ground clip out in the air, I get a noisy ripple with a predictable pattern. Nothing unusual here.

When I touch the tip of the probe to the ground clip, I get a beautiful flat line. Also predictable.

When I take a piece of free wire and clip the ground clip to one end and the probe tip to the other, I also get a beautiful flat line.

When I clip both the ground clip AND THE PROBE TIP next to each other on a ground wire from my circuit board, I get a very similar ripple pattern as in the air.

When moving my probe around in the air, the noise gets louder as I approach my switching power supply. This likely has something to do with the noise in my circuit (if it is even there? Can my circuit cause this behavior, or is it a measurement cravat? Is it behaving like an antenna? How can I improve the reliability of my measurements (spikes are on the order of 100mv btw)?

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  • \$\begingroup\$ you want to improve the reliability of what measurements? ... what are you measuring in mid-air? \$\endgroup\$ – jsotola Nov 30 '19 at 5:10
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I finally found the problem, which was, as I thought, a measurement issue. After removing the probe tip sheath and ground clip, I attached the ground spring that came with my scope and problem solved. I measured a stable zero volts on my circuit's ground rail.

It's No Joke! Use the Ground Spring to make better measurements!

Edit: Here is a short video that explains how the ground spring can improve your measurements: https://www.youtube.com/watch?v=fZ7tOMyi07w

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  • \$\begingroup\$ I'm not sure what a 'probe tip sheath', 'ground clip', and 'ground spring' are. Can you show us a picture or provide links to them? \$\endgroup\$ – Bruce Abbott Nov 30 '19 at 6:04
  • \$\begingroup\$ @Bruce Abbott I added a useful video link! \$\endgroup\$ – Judson Hudson Nov 30 '19 at 19:32

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