Date: Thu, 18 Jun 2015 00:18:28 +0100 (BST)
From: ALAN MELIA <alan.melia@btinternet.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: MF propagation over sea water
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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 : selberdenken@posteo.de
Date : 17/06/2015 - 23:48 (GMTST)
To : rsgb_lf_group@blacksheep.org
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