Hi Stefan, I'm not sure what point you are making here....maximum skywave
daytime range is about 1000km so there is no ground reflection. However a
receiiving station near seawater can get a "coastal effect" which is a bit like
focussing receibing the direct skywave plus a slightly shorter one which is
reflected off the coastal water. This effect is not available on land because
of the larger variations in "roughness" over land as well as its absorption.
Also over water at 400km there is substantial groundwave, though the effect of
this depends on the power radiated and S/N at the receiver For commercial
station (Big antennas) the ground and skywave are around the same strength at
about 700km. Amateur station do not radiate ground wave so efficiently so the
groundwave is maybe about 6dB weaker (this was what we measured at 136 about 10
years ago.) Would that help explain it??
Alan
G3NYK
----Original message----
>From : [email protected]
Date : 17/06/2015 - 23:48 (GMTST)
To : [email protected]
Subject : LF: MF propagation over sea water
Hi MF,
While there is nearly no chance to leave decodes above 400 km in
daylight above land, it seems to be no problem above sea water. As soon
as the first hop (?) hits the ground on water, the wave can travel to
the RX site. At least this attachment shows this effect. The distance
crossed in daylight is about 800 km in this picture.
73, Stefan
|
