[Lf] [Fwd: LF: Antenna measurements/losses/insulators]

[Andre' Kesteloot]

WarmSpgs at aol.com wrote:

> In a message dated 2/26/01 10:28:03 AM Eastern Standard Time,
> j.r.moritz at herts.ac.uk writes:
>
> << ...my favorite theory for
>  the major cause of loss resistance at the moment is that it is
>  caused mainly by dielectric losses in the ground, where the electric
>  field of the antenna penetrates to some depth at LF. This is
>  contrary to the conventional view that the major losses are due to
>  the resistance of the ground system. I don't think there is really a
>  contradiction, just that amateur antennas have relatively high
>  dielectric losses because they are smaller than conventional LF
>  antennas. A bit of thought shows that a predominance of dielectric
>  loss would explain lower loss resistance at higher frequency, and
>  G3AQC's "footprint" effects, among other things. >>
>
> For what it's worth, Jim's theory is entirely consistent with (pardon the
> expression) commercial practice and theory.  I agree that there is no real
> contradiction.  What we as amateurs lump together under the term "ground
> loss" are actually a number of factors, and at LF the dielectric properties
> of the ground certainly are a major component; perhaps _the_ major component
> at 136kHz.
>
> The soil conductivity charts we use to predict groundwave coverage at MF over
> North America differ greatly from the ones used at LF.  Skin depth is a major
> reason usually cited for this discrepancy, along with different assumptions
> about dielectric constant.  The interaction between the ground system and
> losses in the earth extend to a greater depth, where subsoil and rock
> properties may diverge widely from those near the surface.  Thus, not only is
> the apparent conductivity different for MF and LF at any given location, but
> the shapes of the conductivity contours don't bear much resemblance to each
> other, either.
>
> All this appears consistent with what amateurs are finding with practical
> antenna systems at LF.
>
> 73,
> John