DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws;
  s=s1024; d=btopenworld.com;
  h=DKIM-Signature:X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE;
  b=3CccIOtiGe3GvUYdbOLDq1lvRdzZMw1UP44qgmHhm1BQOJIUwhB/XZt0kSEfH98FQ7FINvNy7P2HafqWTZxD70BdfrnKLsuRV5Pmpwk4kMRW2yNStz9LiZsQO+9XiH7EYxmfXQZ3S4LppemtNVeIfqyLjNDWpMRJVT30UGxYgYI=  ;
Message-ID: <9443BF673E7A4E51BBF052ADEA904B4C@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <001201cc6a48$c8123dd0$0401a8c0@xphd97xgq27nyf> <20110903152500.2cbf2a9e@svr1>
In-Reply-To: <20110903152500.2cbf2a9e@svr1>
Date: Sat, 3 Sep 2011 17:33:56 +0100
MIME-Version: 1.0
DomainKey-Status: good (testing) 
Subject: LF: Re: 500 Khz - QSO
Content-Type: text/plain;
	format=flowed;
	charset="iso-8859-1";
	reply-type=original
Content-Transfer-Encoding: 7bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
X-AOL-SCOLL-URL_COUNT: 0  
X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m003.2 ; domain : btopenworld.com DKIM : fail  
x-aol-sid: 3039ac1db40a4e6257387ff2
X-AOL-IP: 195.171.43.25
X-AOL-SPF: domain : blacksheep.org SPF : none


Dear John, LF Group,

> Good signals in daytime - steady with little QSB, but some QRN just
> starting to build. The sea-path down the East Coast must help
> enormously!

Looking at the map, the path Shetland - Scarborough is almost entirely over 
the sea, while Shetland - Lancashire/Cheshire is about 50% over the rocky 
ground of Scotland and NW England. Looking at the ITU ground loss curves for 
500kHz, and applying the "Millington Method" for the appropriate distances 
and ground conductivities comes up with something like 30dB less signal at 
G0NBD/G4WGT compared with G3KEV, even though the distance is similar. This 
is easily enough to make the difference between an audible signal and one 
that would require long integration periods on a spectrogram to detect. It 
might be interesting one day for you to try transmitting slow QRSS signals 
during daytime ground-wave conditions, and see if your signals are 
detectable at inland and western UK locations to make a comparison with 
east-coast locations.

Cheers, Jim Moritz
73 de M0BMU