Egads, you blokes are helpful.

So let me get this right. I am trying to picture Richard's 1/4 wave
radial arrangement. I visualise an upturned umbrella. The spokes are
each 2.5ft long, joined at the middle to the coax shield. The
umbella's handle is also 2.5ft long, connected to the coax inner.

(Does it matter that the local transmitters, so I gather, use
horizontal polarization?)

At the other end the inner is conected to the stub of aerial wire, the
shield to a clamp around the mains cable.

Does the umbrella analogy work for you?

Questions:
How big would the clamp be?
Why not connect shield to chassis?

Not quite clear on two other things, Richard
the inside of his coax cable shield,
Contradiction in terms?

but to connect with the chassis (ground) that many other sets
use for the "signal" connection to the set.
Why should anyone want to connect the signal to ground?

Thanks again
Paul