Thank you to all who made kind remarks and helpful suggestions.

The coil is 18" dia., 24" long, 200 or so turns of 1mm silver plated PTFE
insulated stranded wire. Vario of 600uH included and total available L abt
12mH. Only abt 7mH used. The plastic dustbin that housed the earlier  4mH
coil easily, sits on top of it like a grenadiers shako.
The 'dogbox' is  approximately 1m. cube, and wrapped in a double layer of
1200guage builders poly sheet for waterproofing. ( I NEVER throw out stuff
that just might be useful - some day)
When the increased antenna current was observed the coil was sitting
directly on a concrete path and in the same position relative to brick and
concrete block walls as when finalised, and with the roughcut panels in
their planned  positions as already described.  The only change was to raise
it 5" off the deck so that I could reach the tapping points and the vario.
Four separate checks were made on the improvement on each of the two bands
as things were moved around. But obviously SOMETHING is different - possibly
the earth connection which was remade with a blowlamp today.

Now the sackcloth and ashes - I did not leave a gap in the foil, but after
its removal things were just as per last Friday, - except that the observed
improvement had vanished.
So did a quantity of Pedigree in a drowning of sorrow.

The whole contraption is only intended to survive until we lose 73 KHz,
(after which it will probably become a play hut for visiting grandsons) and
the standard of construction  reflects this, but I am thrawn enough to get
good and mad when inanimate objects develop human  tendencies!

If at first you don't succeed -

Ian MI0AYZ