Earth Mode DX map

This map shows the places round and about my QTH in Burwell (JO02DG) where I was, or was not, able to receive my 4W 838Hz earth mode signal in tests on June 21 and 22nd. Red dots here show attempts that failed, i.e. no signals detected, and green dots show where signals were successfully received and recorded. Best DX was 5.1km, but further is certainly achievable on QRRS3 with "utilities assisted" earth mode i.e. where ground coupling is enhanced by buried pipes and cables. Best DX with 4W into the 20m spaced earth electrodes using purely induction seems to be around 0.5km.