Experience anyone with this one ? Imagine a vertical half folded dipole.
One side is grounded. Like this:

o ____________________________
l
______________________________l
l
ground.

o = input

Drawn laying down but of course it stands upwards. All is a 1/4 lambda long.
But now the trick: a coaxial cable can be shorted at the end too. But the lenghts needs
only be 0.66 times ! So 40 metres high becomes only 26 metres.
Don't bother the shielding, that is no obstacle for magnetic fields.