[Fwd: LF: Effective height of top-loaded Antennas]

[André Kesteloot]

Rik Strobbe wrote:

> Thanks to Peter (G3PLX) for the expanation of the effective height.
> This theory corresponds to one I heard of before, assuming a linear decrease
> of the antennacurrent from feedingpoint to top for short antennas.
> I found a completely other approach in an old German electronics handbook
> (1960's - in later books it is hard to find anything on LF). The theory is
> quite complicated but there the influence of the topload on the effective
> height seems much less.
> I received a mail from G3LDO (also Peter), he put the data of my antenna into
> EZNEC2 and found an ERP of 9.4mW for an antennacurrent of 0.5A.
> If I multiply the height of my antenna (11.5m) with the factor calculated by
> G3PLX (1.84) then the antenna would be similar to a vertical of 21.1 meter
> without top load.
> Put this into the 'classic' formala for a short vertical and you get an
> antennaresistance of 36.5 milliOhm, with a current of 0.5A this results in an
> ERP of 9.1mW - pretty close to the 9.4mW calculated by G3LDO !!!
>
> 73, Rik  ON7YD