Cheap mains conducted emissions tester?

[mtwieg]

If the power lines in your building are heavily polluted with electrical noise, a separate ground connection may reduce the background noise level. You should think about such measures if an "empty" measurement with unpowered DUT shows already a high level near the limit values.
The metal sheet and LISN ground will be normally connected to the regular protective earth.

If the power lines in your building are heavily polluted with electrical noise, a separate ground connection may reduce the background noise level. You should think about such measures if an "empty" measurement with unpowered DUT shows already a high level near the limit values.

For the purpose of testing for high frequency EMI, an earth connection isn't necessary, in principle (though for safety reasons one should still be used). What matters is that your LISN ground is well connected to the DUT ground and the shield. If that's the case, then the LISN should completely isolate the mains side from the DUT side, and vice versa. If the mains interference is strong enough to contaminate the DUT side through the LISN, then an additional line filter on the mains side of the shield may be used.

 

[Velkarn]

did not read all the theme, sorry but
few weeks ago i have visited Lorandt Fölkel emc seminar, where he showed his diy lisn (its 50mmx30mmx40mm) and he says that some conducted emi measurments (not quite correct, but "pre") can be made with this lisn and oscilloscope