Hi Markus, ELF, Oh, maybe you're right. The spectrogram is in 45 mHz and 5 s/pix scroll rate. Attached is the recording in 11 mHz and 30 s/pix, see the long-term average graph, red. No noise blanking
Stefan, my impression was that ELF levels were slightly stronger in daylight; for the 60 Hz "TA slot" this seemed to be during our evening. But the diurnal differences were not large, maybe 2 or 4 dB
To whom it might concern ... The US power grid 60 Hz spectral line is also detectable in Europe. See attached spectrogram I recorded with an e-field receiver (1m long vertical whip + FET/BJT cascode