[BC] dtm

[Clive Warner]

>2. Is there a practical way to electrically shorten such a radiator? For
>example, can you attach a skirt to the bottom and drive it so that the
>skirted section (in this case something between about 40 degrees and 100
>degrees) does not radiate?

Do the math.
I am pretty certain that if you tried such a thing, it will not be
practical.
You only have to look at the equivalent circuit.
Surrounding the lower section with a cage, the cage being earthed, and this
is a series driven radiator I assume?
The section, you'd think, will act like a transmission line? Sort of, but I
think it will look just like an electrically short, shorted stub.
Now put that in parallel with the fundamental impedance of the antenna and
do the parallel-to-series conversion and tell us what the figures are
please.
And in any case there is no such thing as 'ground', any such aerial
structure is rather likely to radiate. Unless of course it is a quarter wave
high to the unsleeved part, in which case you'll have a sleeve dipole and it
will work fine. . .

My honest opinion:
Any such idea is crazy Heath-Robinson stuff.
The correct method is to call in a competent steelwork contractor who will
separate and jack up the top part of the structure enough to install an
insulator at the optimum desired electrical height.
- Clive