Some months ago - time flies, so it may have been last year - someone kindly sent me a copy of a paper, or at least a formula, to work out the radiated power (as opposed to other forms of signal transmission) from an earth-electrode pair "antenna" at ELF. I think it was based on some of the Project Sanguine work at 76Hz back in the 1970s. I thought I'd saved this, but cannot locate it anywhere.