After moving into a new house I plugged my oscilloscope in and turned it on. After booting there is a constant 1.4-2.0 MHz signal being picked up. If I ground the scope with my hand on the probe lead it doesn’t produce the expected mains hum.

Disconnecting the probe however produces the mains hum as expected.

I have tried switching probes, channels, and plugging it into a socket directly instead of a surge protector in case the surge protector earthing is bad. None of it solves the problem. Holding the probe up to various electronics equipment doesn’t produce a difference in signal. Raising the probe up and down seems to alter the amplitude but not the frequency.

What could be the issue? This is rendering my scope unusable.


I am using a Rigol DS1054Z. I have driven around a few blocks in any direction and I don’t see any towers that would be a source of distortion. I am near a WiFi router (the one I’ve always had) but that is operating at 2.x and 5.x GHz.

I am operating the probe in 10x but turning that off doesn’t do anything.

The period of the signal is around 500-900ns. The frequency varies between 1.13 and 2.59 MHz.


Took a multimeter to my sockets and discovered while it appears to be grounded, hot and neutral are reversed.

It would appear my oscope is ok. Connecting probe to test and grounding the plug on one of the bnc channels produces a clean square wave after hitting “auto”. Will need to construct a loop antenna to find the source now.

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    \$\begingroup\$ Is your new house close to a broadcast radio or TV tower? Close to some cell phone antennas? What is the amplitude of the unwanted signal? How are you connecting the probe's ground wire during these observations? \$\endgroup\$ – Elliot Alderson Jul 7 at 17:27
  • \$\begingroup\$ I haven’t investigated further than the house. I know the former owner had a satellite dish mounted but it is disconnected. No idea on towers. Connecting ground and probe to the calibration posts shows the expected square wave but extremely noisy as a result of the signal. I can get you more information when I return home in around 30 min \$\endgroup\$ – CL40 Jul 7 at 17:38
  • \$\begingroup\$ Scope model could also be useful while you're editing your post. \$\endgroup\$ – pipe Jul 7 at 17:46
  • \$\begingroup\$ Finger to probe tip gives AC E field while not touching probe or any other ground. Is your house outlet earth grounded? \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 7 at 17:54
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    \$\begingroup\$ go to another location away from your house .... does your scope exhibit the same problem there? \$\endgroup\$ – jsotola Jul 7 at 19:20

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