At 2.4km good copy on the Spectran display
At 4.6km clear copy on the Spectran display.
At 8.6km the signal was detectable, but weak (see picture attached from Spectran screen).
These reports are roughly "end on" to the electrodes and I've yet to try other directions such as orthogonal to them. No attempt was made to match the PA output to the impedance presented by the earth electrodes which are around 40-60 ohms below 10kHz; I've not measured it at 136kHz yet.
Even with true QRP it looks like a range of at least 10km should be possible on QRSS3 (and probably WSPR) with a half decent receiver (better than my crude set-up) using just a 20m earth electrode TX antenna on 136kHz. I'll leave the QRSS3 beacon running over the weekend on 136.93kHz from my QTH in Burwell, Cambs (JO02dg) and any reports and screen shots would be much appreciated.