Today I managed to copy my 4W earth mode 838Hz signal at a range of 5.1km. QRSS signals were so strong that I was able to copy by ear my 10wpm CW beacon too! To copy the 10wpm signal I needed Spectran running with narrow bandpass filters. Without the filtering, all that could be copied was 50Hz noise. At this range the signal level is definitely being helped by conduction through pipes in the roads and the main propagation is not by induction. Lots more information as well as screen shots and recordings on my sub-9kHz webpage.