[Lf] [Fwd: LF: Re. LF Top Loading]

[Andre' Kesteloot]

LAWRENCE MAYHEAD wrote:

>  Hi Stewart,I agree that top loading improves short
> vertical antennas,it seems in two ways:-1) Pulls the
> current higher up the vertical section and makes it more
> linear thus increasing the effective height (the current
> in a long vert is sinusoidal but can be made almost
> constant with enough top loading) An elevated inductor can
> also beused to improve the effectiveness of the top
> loading,but there is a trade off against loss in the
> inductor.2)The more the top load wires can "see" clear
> earth beneath and around, the lower the loss resistance!
> Parrallel wires reach a limit quite soon because they are
> "seeing" the same ground, there is also a point at which
> the capacitance ceases to increase,probably for the same
> reason. In my opinion, supported by much experimentation
> it is better to extend the wires so as to cover as much
> virgin ground as possible.I think this is why so called
> "long wires" work well on LF. It is however not
> necessesary that the wire should extend in a straight line
> it can double back on itself once or twice, the aim being
> to expose as much ground as possible to the wires.I have
> not workede out how close these zig zag wires can be, but
> empiricaly an angle of 30 to 45 degrees ( seen as a cone
> or spray from the wire ) will result in reduced loss
> resistance. I have dramatically reduced my loss resistance
> by means of this technique from over 100 ohms with a three
> wire top to 80 ohms by extending in a straight line and
> now to less than 40 ohms with my current system which
> consists of a 15m vert section with two top wires one only
> 20m long but the other in a "V" shape 75m long. The
> estimated Rres is about .07 ohms. Thing is to get as much
> wire up there as possible but it doesnt have to be
> straight.Re NEC, I use Eznec to model all my Ants and it
> is very useful but it does not deal with the earth very
> well, and so far as I know none of the available programs
> do.So yes use it to sort out various configurations but
> there is no substitute for trial and error in the last
> resort.I belive the figures obtained for R res using  the"
> perfectearth" zero loss etc are reliable. Best wishes 73s
> Laurie G3AQC.