On 10 march 2017 Stefan DK7FC experimented with transmitting on 2970Hz. The signal was received in Todmorden, England by Paul Nicholson at a distance of about 850km!
The above spectrum is the result of adding the spectra in 1.22uHz bins from 13:00- 24:00 UTC each day between 20170317 and 20170320. Paul uses two crossed loops for H-field and an E-field active antenna, this enables synthesis of a highly directional antenna.
This is a historical moment, because it’s the first amatrur transmission on ULF to span such a distance. The distance is about 9 wavelengths, which is well into the far-field region.
Amateur experiments on very low frequencies should also be of interest to the scientific community. Most of avaliable data is for frequencies above 10kHz or for the military stations on 82Hz and 76Hz.