[Fwd: LF: Ground systems and first tuning results]
Tue, 27 Jul 1999 20:31:45 -0400
> Edited parts of what Hans-Joachim Brandt wrote:
> > For LF I can use either the house ground, which is also connected to the water
> > pipe net, or a radial ground made of 28 insulated litz wires with lengths
> > between 12 meters and 30 meters depending on the available space in that
> > direction.
> > When working on this radial system and continuously measuring the feed point
> > resistance under resonance conditions, however, I could not confirm Bobs remark
> > that metal stakes at the far ends would give an improvement.
> At my QTH, I too did not notice any difference in "before" and "after"
> connection of outer end earth stakes (but I left them connected anyway
> >At least on my
> > insulated radial system the feed point resistance increased. Especially with
> > rather few radial wires the radial ground had been very sensitive against any
> > ground connection, including a simple earthstake connected to the centre of the
> > system. After the number of radials had approached 18 the earth stake
> > (just a few inches deep) connection to the centre could be tolerated, but never
> > the connection to the house ground. Once I have tried to elevate all my radials
> > about one foot from the ground: The feedpoint resistance remained the same, I
> > needed more inductivity in the variometer, and the sensitivity to any connection
> > to ground even increased! This sensitivity obviously depends of the capacity of
> > the insulated radial system to ground.
> I use buried bare copper radials. However, regarding above-the-gound
> insulated radials, like those mentioned, the explanation could be that
> the "return flux" finds it easier and lower loss to return as current to
> the antenna feedpoint via the copper, which being insulated from ground,
> has no possibility of contacting lossy soil.
> Further, when selected (tuned) inductors are used between the feedpoint
> and insulated radials, then it becomes even more attractive for the
> "return flux" to terminate on the wire rather than ground, as with
> "tuning" the insulated radials can be "-" potential when the driven
> antenna is "+" potential, and the soil somewhat neutral potential. I
> have seen some diagrams of commercial stations where the connection to
> actual earth is tapped from the central part of the loading coil, and
> apparently adjusted for least current in the connection to ground.
> Least "wasted current" to ground likely concurs with highest antenna
> efficiency with most current collected by the low resistance insulated
> radials. As already mentioned, being "antiphase", they can attract more
> flux than if they were neutral.
> This favours above-the-ground radials, and more complicated tuning,
> however in most domestic situations these type of radials become a
> severe nuisance for tripping over, cursing the designer, etc :(
> Bob ZL2CA