Electronics > Beginners

Oscilloscope interference.

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GadgetBoy:
Having an issue with my new oscilloscope. It was picking up a LOT of HF interference from *somewhere*, and after some troubleshooting, I was able to track the interference down to my LED driver for my workbench lights. It is pumping a lot of HF into the air and into the mains, and I'm not too sure what to do about it. I bodged in a hand-wound common-mode suppression choke on both the mains and DC sides of the driver, Put a ferrite bead on the power cord at the plug, and ferrite beads on both the +ve and -ve wires right against the LEDs. The interference has lessened somewhat, but it's still buggering up the trigger on the scope. Any thoughts? First picture is with the driver plugged in, second picture is with the driver unplugged. The scope probe is not connected to anything at all.

bob91343:
The problem may be that the probe isn't connected.  If you unplug the probe from the 'scope, does the signal disappear?  Or try shorting the probe to ground.

The question is, where is the signal getting in?  Via the probe, the power line, radiation, etc.?  One you figure that out you can take steps to eliminate it.

GadgetBoy:

--- Quote from: bob91343 on July 06, 2019, 02:03:01 am ---The problem may be that the probe isn't connected.  If you unplug the probe from the 'scope, does the signal disappear?  Or try shorting the probe to ground.

The question is, where is the signal getting in?  Via the probe, the power line, radiation, etc.?  One you figure that out you can take steps to eliminate it.

--- End quote ---
Probe is connected, without it connected, it goes away, so the probe is acting like an antenna of sorts.

It seems that it also comes in through the mains, though, as it shows up connected to an entirely different outlet.

Sent from my ONEPLUS A3000 using Tapatalk

JustMeHere:
Did you watch Dave's video on this?

GadgetBoy:

--- Quote from: JustMeHere on July 06, 2019, 02:36:29 am ---Did you watch Dave's video on this?

--- End quote ---
Which one? I've seen a few of his recent ones, but not one that addresses this particular issue. Link?

Sent from my ONEPLUS A3000 using Tapatalk

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