Topband: chicken wire ground screen (reply to W4EF comments]

[Dave Bowker]

In Response to W4EF's and other (private email) comments:

There are three different [primary] currents in effect beneath and around a
vertical radiator operating over earth and above an artificial  ground
plane. These are (1) conduction currents, (2) induced currents, and (3)
displacement currents.

The conduction currents (1) originate at the feed point of the element,
circulate through the ground outwards and towards the surface, and in the
process, create or "induce" (2) induced currents beneath the surface, then
proceed radially towards the surface where they exit and become (3) radial
displacement currents which return to the vertical element via the
atmosphere.

The induced currents create and generally [aid] or strengthen the conduction
currents [VERY] near to the base of the radiating element, but [oppose] the
conduction currents further out from the base of the element and within the
subsurface of the earth, before the conduction currents exit the surface as
displacement currents.  At or very near to the surface (where the iron
mesh/chicken wire lies), both the induced currents and conduction currents
[will] induce an eddy current [considered to be a "secondary" current] to
flow into [any] closed-loop ferromagnetic circuit, that is, each
retangular/hexangular portion of the chicken wire or fencing mesh acting as
the ground-plane.

Galvanizing, zinc plating, copper plating, etc. and the thickness/skin
effect considerations of such coatings, offer [absolutely NO] shielding
effectiveness against the electromagnetic fields nor do they provide [any
attenuation] of induced eddy currents into the ferromagnetic material, which
as I previously stated in my postings is the predominant field surrounding a
vertical radiator of 1/4-wavelength or less, and such platings/coatings
contribute [nothing] to deterring the effects of eddy current losses (Joul
heating) in the iron mesh itself.

Bottom line:  ANY loss incurred by a mesh-type of ground screen by induced
eddy losses adds to the overall system losses.

The most effective and lowest loss method of returning conduction and thus
displacement currents (the desired ones) to the "vertical system" is via
[RADIAL] wires extended outward from the feed point of the vertical element.

73, Dave, K1FK
Fort Kent, ME