EZNEC modelling software is capable of modelling the ground influence on
antenna feedpoint Impedance and conductor conductivity.
By comparing a model with zero conductor resistance and perfect
ground with a real world model it can estimate efficiency. From this
actual radiated power from the antenna can be determined and was used
in the first round of discussions on 'ERP' (about 16 months ago). The
results correlated well with measured signal strengths.
see page 6.9 of 'The LF Experimenter's Source Book' on Computer
Modelling of LF Antennas
The best efficiency I was able to get from my antenna was about 400mW
radiated (erp?) from a transmitter power of 300W, about 0.13% efficient.
Regards, Peter, G3LDO