Recalculating 472kHz ERP

Yesterday I said I would recalculate the ERP of my earth-electrode "antenna" in the ground at 474kHz. This is proving much harder to work out, not helped by living in a continual "brain fog" since my 2013 stroke. Even simple tasks, whether physical or mental, are now so much harder.

I seem to be coming up with silly figures (much less than 10mW ERP) and these depend on some assumptions about the effective area of the loop in the ground, which are an educated guess. Either the effective loop is much bigger than I expect or the ERP is far less than 10mW!! A recalculation is needed.