[Fwd: LF: Horizontal polarisation on LF?]
Fri, 16 Jul 1999 21:14:12 -0400
> Hi all,
> Taking up the thread of the ERP discussion, and consideration of
> verticals or a dipole:
> At the rather long wavelengths of interest, amateur antennas at LF are
> usually very short in electrical length terms. The presence of "earth"
> can not be separated from the antenna environment. The "earth" is a
> combination of conductance and dielectric. The launching of a radiated
> wave is greatly facilitated by using the ground conductivity, and is why
> VERTICAL POLARISATION is the main mode of antenna operation, and ensuing
> GROUND WAVES are relied on for reliable coverage (at least that is the
> reasoning for most of the broadcast and military LF systems). Usual
> practice is to have a "big antenna with lots of top loading" and "lots
> of ground radials". LF amateurs are mostly building small scale
> versions of what the "big boys" do i.e. a Marconi T or variant.
> However, the best of amateur LF DX is usually a result of SKY WAVE
> propagation, even if the amateur antennas are vertically polarised (the
> polarisation reflected by the ionosphere could be random, but only the
> vertical component is efficiently received). If sky wave mode is what
> is actually being sought after, then it may well be worth experimenting
> with a horizontal "dipole"? The ground conductivity will try to "short
> out" the launching of a ground wave, but who cares if sky waves are the
> desired main objective? A horizontal wire electrically close to ground
> provides a "near vertical incidence" radiation pattern, with most power
> "going upwards", but with sufficient angular spread to provide
> reasonable DX from a one hop path via an ionospheric reflection.
> One New Zealand amateur, Bruce ZL1WB, uses a very long wire strung out
> over a gully, and with only 30 watts of RF power applied, is the most
> often copied ZL LF amateur station in Australia (spanning the Tasman
> Sea, a definite sky wave path, signals are zero much of the time during
> daylight hours). So there is a suggestion that the very long wire that
> is mostly horizontal in nature does provide good LF DX.
> So, casting aside the preconditioning about vertical polarisation and
> LF, I suggest that it would be well worth investigating from the point
> of view of sky wave DX potential.
> Does anyone have a back yard that is a half wave across on LF :) I do
> not :(
> Bob ZL2CA
> PS I would ask Finbar if he could erect a second big mast for the other
> end of an LF dipole?