At one time I was very active monitoring amateur radio below 10 kHz. Stations from all over Europe were decoded. I also used to regularly run a website dedicated to amateur experiments at the very low frequencies. Some remarkable distances were spanned.
To TX, very big antennas are needed. For RX an E-field probe, which is tiny, is very effective. Extremely accurate frequency control is essential. This is usually achieved by GPS locking or locking to a VLF MSK signal, which is what I did. Bandwidths are measured in uHz. Timescales are measured in hours or even days! Casual listening is extremely unlikely to result in success, except perhaps by earth-mode over much shorter ranges.
Since my 2013 stroke, I have not been active below 10 kHz. Experiments continue and keen amateurs are still knocking on the boundaries and achieving what many thought was impossible.
The photo shows my reception of
DK7FC in 2011. In more recent times he has been testing on ever lower frequencies and with earth-electrode antennas.