D. Heizinga wrote:

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.

The antenna as drawn is a common folded monopole
configuration for VHF antennas.

What you are proposing using coax would simply be a shorted
1/4WL stub with very little common-mode current and therefore
very little radiation. Virtually all of the current would be
contained on the inside of the coax and the feedpoint impedance
of the shorted 1/4WL stub would be extremely high. If one could
succeed in shoving some current into that sky-high impedance, the
major losses would be I^2*R and dielectric with very little
energy "lost" from the system as radiation - bad idea.
--
73, Cecil http://www.w5dxp.com