Hi, Jim and Group
On Sat, 26 Jun 2004, James Moritz wrote:
lot of difference to the distribution of current. For a wire near ground
level connected to a ground spike at the far end, I reckoned that the
inductance was of the order of 1uH/m,
If we describe this inductance as inductance of shorted piece of guid line
we can easy get a formula:
L/l = (Zw/Zo)*mu0
where Zw is impedance of line, Zo is impedance of space (377 Ohm) and
mu0 is magnetic constant (1.26 uH/m). So Zw is about 300 Ohm. It is
reasonable (1/2 of impedance of line, wich consist of wire and its mirror
image in the ground)!
systems, which gave better performance with fewer maintenance problems.
As discussed on the reflector some time ago, and based on this and other
experiments, I came to the view that for typical amateur antennas, the
majority of the loss occurs as dielectric loss in the ground due to the
electric field of the antenna, instead of in the ground return path
resistance,
I have study this kind of loss (dielectric) theoreticaly. It much decrease
if one use elevated radials, not burred. But in this case seems 'ground'
system should be isolated good from real ground (it is worth!). Certanly
one should use a transformer to feed such an antenna (TX box is
connected to a ground usualy). Height of radials should be about
0.5 - 1 m. Certanly this is reasonable only if there is no trees,
buildings and so on around an antenna.
Unfortunely I have no oportunity to do comprehensive experimental test of
this.
73 de RA9MB/Alex
http://www.qsl.net/ra9mb
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