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The mains of my German flat has 19kHz electrical fields on hot, neutral and! ground wire. I don't have to get rid of them entirely but I want to achieve 20dB reduction while sitting in front of my computer with grounded power supply.

How to achieve this goal?

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    \$\begingroup\$ If it's on ground, too, it's most likely the auxiliary carrier of FM stereo picked up by your measurement equipment out of the air. To get rid of it, move to the basement. Caveat: radon levels in the basement are often unhealthy in the long run. \$\endgroup\$
    – Janka
    Commented May 18, 2020 at 22:32
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    \$\begingroup\$ Why do you have to get rid of them? \$\endgroup\$
    – JYelton
    Commented May 18, 2020 at 22:50
  • \$\begingroup\$ Thanks! Actually "19kHz" is 3 peaks at 16, 20 and 24kHz, don't know why I burnt 19kHz to my brain. Didn't think it would be this important. Is "Frequency modulation synthesis" a good start point to check out what you mean with "auxiliary carrier of FM stereo"? What stands against your statement is that it is strongly depending on daylight, so I thought it would be a solar voltaic. \$\endgroup\$ Commented May 18, 2020 at 22:51
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    \$\begingroup\$ "FM stereo" is your good old radio. Stereophonic radio has an auxiliary carrier on 19kHz for the second audio channel. \$\endgroup\$
    – Janka
    Commented May 18, 2020 at 22:55
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    \$\begingroup\$ If it's dependent on sunlight, it may as well be a solar inverter on a nearby roof. But again, if you can measure it on the ground line, it's not coming by wire. The wire only picks it up better as if you held your measurement tip right into the air. To check that, connect a loose end of some metres of wire to your measurement equipment as an antenna. \$\endgroup\$
    – Janka
    Commented May 18, 2020 at 22:57

2 Answers 2

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As others stated,the cause of the radio frequency interference (RFI) is likely separate inverters for a solar power system.

You can easily calculate values for an L-C filter for ~20 kHz region. About 10 nF and 6.3 mH, for example,should block most of that RFI coming over the wires. That said, you'd need an effective ground, e.g. a copper water pipe, to connect to the capacitors.

However, since the solar panels have comparatively high currents, you'll also have problems from the radiated magnetic field inducing 20 kHz in a length of wire, such as power cords and USB cables. You probably can't build a mu-metal shielded room, so get as far from the inverters and panels as possible. For sensitive measurements, run from battery (not UPS, which have their own inverters).

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  • \$\begingroup\$ I wanted to avoid to tinker with 230V but maybe it's necessary. Needs a lot of preparation then. Infinite Impedance at resonant frequency sounds too nice. My heaters should make a good ground. \$\endgroup\$ Commented May 19, 2020 at 21:15
  • \$\begingroup\$ @Hansebenger, what problem is the RFI (actally, AFI, audio frequency interference) causing? Shocks from touching the PC? Audible noise? Display issues? False measurements with a PC oscilloscope? Something else? \$\endgroup\$ Commented May 19, 2020 at 22:15
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Some lighting systems use ‘high frequency’ ballasts in that range. Also may be noise from a switching power supply, or even a variable-frequency motor drive.

Use an AC power line filter to suppress it.

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  • \$\begingroup\$ I have tried two AC power line filters theoretically barely fitting without success, maybe you know some more special? 19kHz seems to be a tough number for normal power line filters. \$\endgroup\$ Commented May 18, 2020 at 23:46
  • \$\begingroup\$ Maybe there’s a fault on ground - line filters shunt some noise back to ground. \$\endgroup\$ Commented May 18, 2020 at 23:49

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