Yesterday, I replaced the wire that I used successfully on 472kHz WSPR TX with a very low ERP.
It was also used successfully on 160m and 80m.
As yet, it has still to be tested.
UPDATE 0940z: Tested on 160m and 80m. Still high VSWR. Totally puzzled.
UPDATE 1538z: I cleaned the contacts at the far end and the VSWR remained high on 80m. With the auto ATU it matches on 160m. I have not tried 630m, which needs the transverter. My conclusion is that over the years tree roots have grown and effectively shorted out across the "loop" in the ground rendering this "antenna" no longer useful. I may try 160m WSPR or FT8 tonight, but may remove it tomorrow.