[Fwd: LF: ground loss problems]
Sun, 17 May 1998 17:15:33 -0400
Peter Martinez wrote:
> >From Peter Martinez G3PLX Kendal Cumbria.
> Regarding Rik's loss measurements, all the figures seem
> reasonable to me, and are similar to those that I got when
> experimenting with a 12m vertical. This had no top wires (it was a
> whip antenna), four 12m radials, and was well clear of any trees.
> I reasoned that the loss resistance that is being measured is not
> just the series resistance in the ground lead, but includes a
> component that is effectively the series-equivalent resistance of the
> parallel loss that is inherent in the capacitance to (lossy) ground
> from the antenna. Each element of this capacitance has it's own
> series resistance, so that the total antenna capacitance to
> ground has a series resistance. This can be converted to an
> equivalent parallel loss, then the (lossless) capacitance of the
> antenna to the rest of the universe can be added, then the whole
> thing converted back to series-equivalent. The only way to eliminate
> this kind of ground loss would seem to be to screen the ground from
> the antenna, and in Rik's case, screen the trees too. Maybe
> extending some of the radials up the outside of the offending trees
> would help, but maybe not if this ends up screening the antenna to
> some extent, which is the same thing as saying that it reduces the
> radiation resistance of the antenna.