Re: Ground Plane/ Volumetrically Inefficient Secondary?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Mddeming-at-aol-dot-com>
> 
> In a message dated 5/26/02 3:10:26 PM Eastern Daylight Time, tesla-at-pupman-dot-com
> writes:
> 
> >
> > What about the magnetic effect the ground plane- might  it not be better to
> > use
> > a star-shaped ground plane rather than a solid sheet of metal or foil to
> > prevent induced current from flowing in the ground plane and causing energy
> > losses?
> 
> To minimize the eddy currents in a ground plane, many folks have used wire to
> form a 3-4ft diameter wheel of 50-250 spokes, with the TC centered on the
hub.
> Matt D.
> G5-12

	A general rule of thumb for large vertical antennas is that a ground
plane of radius equal to the height of the antenna is almost as
effective as an infinite ground plane, but a lot cheaper.  In his "Radio
Antenna Engineering" LaPorte shows ground plane effectiveness as a
function of the number of radials.  The point of dimishing returns is
reached at around eight.  The purpose of radials is to reduce the amount
of copper required, compared to a solid plate.  In the case of a TC with
the primary close to the ground plane, the use of a radial system of
wires might reduce the change in inductance due to the presence of the
conducting surface.

Ed