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Oscilloscope probe ground leads act as FM attennea
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Martin72:

--- Quote from: Martin72 on October 25, 2023, 07:22:46 pm ---This is a disturbance that probably comes from the power supply.

--- End quote ---

No:

https://www.eevblog.com/forum/testgear/rigols-new-dho800-oscilloscope-unbox-teardown/msg5139402/#msg5139402

Must come from the "inside"... ;)
ebastler:

--- Quote from: Fungus on October 29, 2023, 09:08:22 pm ---Do you live near a local FM radio station?

--- End quote ---


--- Quote from: dmulligan on October 29, 2023, 08:59:28 pm ---[...] my problem seems to be coming from a few locations with line of site through my window from 5 to 8 KM away.  All (most) of the FM and TV transmitters in my city are arranged along a long hill across the river valley from me, all visible from my window.

--- End quote ---
dmulligan:

--- Quote from: Martin72 on October 29, 2023, 09:04:53 pm ---Hm, look like the full FM band 87.5Mhz-108Mhz... ;D
Won´t believe that this is the cause, but you could try it like I did:

https://www.eevblog.com/forum/testgear/new-dho804-does-this-compensation-signal-look-noisy/msg5134284/#msg5134284

--- End quote ---

Thank you for making me look back at the way you zoomed in.  My noise is much higher frequency than yours.  The first three captures are as similar to yours as I could make them.  I didn't set the vertical cursors until the last two captures.










Martin72:
Modulated signal....Your scope is receiving... ;D
dmulligan:

--- Quote from: tautech on October 29, 2023, 09:05:30 pm ---~90-100 MHz is FM broadcast.
Careful probing technique is required with low level signals.

--- End quote ---

The signal in question is the 3v calibration signal where I am measuring 300-500mV of noise on it, depending on conditions I have yet to narrow down.  Not quite true, 2 meters to my left and the scope turned to a different orientation I was seeing only 150mV of similar looking noise.  I am trying to determine if the noise is something I can avoid or if I live in a noisy area and all signals require careful probing technique.
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