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

**André Kesteloot**
akestelo@bellatlantic.net

*Wed, 29 Apr 1998 13:26:40 -0400*

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
*