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Re: LF: MF propagation over sea water

To: [email protected]
Subject: Re: LF: MF propagation over sea water
From: ALAN MELIA <[email protected]>
Date: Thu, 18 Jun 2015 00:18:28 +0100 (BST)
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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 : [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


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