[Lf] [Fwd: LF: Transatlantic]

[Andre' Kesteloot]

WarmSpgs at aol.com wrote:

>       Dave Brown writes:
> >That said, the use of larger verticals will not necessarily give the best
> >takeoff angle for the relatively poor skywave that they tend to produce.
> >Bigger ain't necessarily better in such cases. This is of course in direct
> >conflict with 'conventional' wisdom that is based on commercial practice
> >using groundwave only, not amateur 'limited' comms
>
> Not exactly.  Commercial and military practice at MF and below often entails
> use of skywave, too, and we specifically use large verticals for their
> low-angle radiation characteristics to achieve best long range coverage.
>
> The objective is twofold:  To minimize high angle radiation that sometimes
> results in  destructive interference to our groundwave (not a prime
> consideration for this effort, of course), and to maximize it at angles where
> the fewest possible hops will be required to reach the target, as multiple
> hops are disproportionately lossy.
>
> Angles of departure well under five degrees will be necessary to cross the
> Atlantic in two or three hops.  An angle of 20 degrees could easily entail as
> many as 10 hops, with consequent extra loss.  However, one must get beyond a
> quarter wave antenna height before the vertical radiation pattern begins to
> concentrate significantly below 20 degrees.
>
> I doubt many amateurs, even in the wide open spaces of Scotland, are likely
> to have, say, a half wavelength vertical at their disposal for 136 kHz. <g>
> But bigger can still be better.  Anything that minimizes the number of hops
> will prove worthwhile; as, for that matter, will anything that makes it
> possible to achieve a full one watt ERP.  Larger antennas will certainly
> help, as will any and all loading tricks to linearize current in the vertical
> run.
>
> 73,
> John  KD4IDY