This evening I repeated my visit out in the fens with my loop seeing how far I could copy my 4W 838Hz beacon. After getting good QRSS3 copy at the same location 5.1km out as 2 evenings ago, I then tried going further out along the same fenland drove road. Although I managed to copy the signal at 5.25km this evening, no copy was achieved at any greater range despite travelling along several different lanes in many different directions. I'd like to know what it is in the roads that is helping - I assume water pipes, but it could be gas pipes or buried cables. What is clear now is that without these, the signal is absent more than 0.5km from home. This time I tried looking for the signal in far more places about 4-6km to the north of the village, but there was no trace of signal in this direction. Best directions are west (fenland peat) and south (chalk uplands). I've still to test to the east.
Another future test will be to try receiving the signal with a second pair of earth electrodes instead of the loop at some distance from home as one might expect stronger signals. This test will have to wait until the weekend though. If similar to results close to home, the 50Hz noise will be much worse though and this may prevent reception unless very quiet spots can be found.