LF propagation over water

[Andre' Kesteloot]

Mike Dennison wrote:

> ON7YD wrote:
> > Last night I heard several UK stations working OH1TN and giving him good
> > reports (559 and better). At the same time I could copy OH1TN only 439.
> > The distance for the UK stations and for me is in the same 1800 - 1900 km
> > range (some UK are a few 10's of km closer to Reino, others a few 10's of
> > km further away).
> > The only differences I see right now are :
> > 1. Assuming that propagation is 1 hop E layer reflection the reflection
> > point is about 100 to 150 km further north for the UK stations.
> > 2. The path between Reino and the UK stations is about 60% sea / 40% land
> > while the path between Reino and me is about 10% sea / 90% land (although a
> > big part of the land path is over Sweden, close to the Baltic coast.
> >
> > I think that groundwave propagation over 1800km with less that 1W ERP is
> > rather unlikely, so 2. may be of no importance.
> > The observation that there seems to be a correlation between high Ak values
> > and good 'long distance' LF propagation could suggest that this type of
> > ionospheric propagation is ebhanced over more northern paths (similar to
> > 'Aurora' on VHF).
>
> Don't ignore the effect of the sea path. Even at HF where all
> propagation is by sky wave, stations near the coast have an
> advantage. I think this is because the signal which goes skywards
> is not a narrow beam (as is normally shown on simple illustrations
> of how the ionosphere works) but a broad beam which includes a
> great deal of RF reflected (refracted) from the ground at quite a
> distance from the Tx. The amount refracted, rather than absorbed,
> will be affected by the ground conductivity, of course. But you may
> also be right with point 1, too.
>
> Mike, G3XDV (IO91VT)
> http://www.dennison.demon.co.uk/activity.htm