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There is a house connected to German mains with hot, neutral and ground. Some distance away in the village there is a PWM source (most propably a solar inverter) which shows as 17kHz on the mains between hot and neutral. I have a capacitor of 2µF in the house between hot and neutral which I can turn on and off and my goal is to mesaure the state of this by measuring radiated electrical fields at 17kHz at the other side of the house at another floor.

I measure with an oscilloscope with the probe connected to a 16m wire floating in the air with 50cm distance to any mains wiring except ground. 1m of the wire is unwounded, 15m are wounded as a coil, see the picture if unclear. Oscilloscope ground is connected to mains ground. Ocilloscope has 71pF voltage measurement including its probe. Antenna with oscilloscope probe

I modelled the situation as following:

  • R and jR2 are the internal impedance of the 17kHz source, not 0
  • C Ant is the emitting of the mains and picking up of the electrical field by the wire
  • C Osc is the capacitance for measuring voltage by the oscilloscpe

model

In theory I expect the measurement values to get lower when the 2µF capacitor is turned on because there now is a path with lower impedance and the internal impedance of the source is not 0, so the source has not enough power to hold up voltage at the high impedance path I measure. But in pratice the measurement values when turning on the capacitor get higher and this is uncorrelated with distance to the capacitor.

Does my measurement setup not measure electrical fields? I am not 100% sure if picking up of electrical fields by my antenna can be modelled as capacitor C Ant? Ultimately I am interested in a measurement setup where the measurement values get lower when the capacitor is turned on with the following rules:

  • measuring between air and mains ground
  • 50cm distance to mains wiring except ground
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  • \$\begingroup\$ What's the point of the antenna? Why not just measure the voltage of the 17 kHz signal directly on the mains, with and without the 2 µF capacitor? In any case, the coiled-up part of your long wire is doing you no good at all. \$\endgroup\$
    – Dave Tweed
    Commented Mar 18 at 12:36
  • \$\begingroup\$ Measuring in air is more fascinating and more secure than measurung with mechanic connection. Never connect an oscilloscope directly to mains, see electronics.stackexchange.com/questions/674280/… . \$\endgroup\$
    – Hansebenger
    Commented Mar 18 at 13:40
  • \$\begingroup\$ I have re-measured with a shorter wire without a coiled-up part, same result. \$\endgroup\$
    – Hansebenger
    Commented Mar 18 at 13:41
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    \$\begingroup\$ RE: Mains, Never use absolutes. :) You just have to do it correctly! \$\endgroup\$
    – Aaron
    Commented Mar 18 at 14:43

1 Answer 1

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I have reworked my measurement setup: I installed 10µF capacity at each phase and measured one floor higher in the building than in the original measurement setup.

I now see lower measurement values when the capacitors are turned on in comparision when they are turned off, as I expected.

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