Stefan DK7FC did a succesful transmit experiment utilising a ground diole on VLF. This resulted in a really strong signal on our Warsaw grabber (over 900km distance):
The spectrum after amplitude normalizastion:
The antenna had about 900m and the current was about 1A. A full descrption is avaliable in the rsgb-lf-group list archives:
https://klubnl.pl/rsgb_lf_group-archives/html/rsgb_lf_group/2018-12/msg00557.html