Return-Path: Received: from mtain-mg06.r1000.mx.aol.com (mtain-mg06.r1000.mx.aol.com [172.29.96.206]) by air-df05.mail.aol.com (v127_r1.1) with ESMTP id MAILINDF054-5ef54b9fd0555; Tue, 16 Mar 2010 14:39:18 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-mg06.r1000.mx.aol.com (Internet Inbound) with ESMTP id C2A2C380000B0; Tue, 16 Mar 2010 14:39:14 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Nrbef-0006Qr-QY for rs_out_1@blacksheep.org; Tue, 16 Mar 2010 18:38:13 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Nrbef-0006Qi-8n for rsgb_lf_group@blacksheep.org; Tue, 16 Mar 2010 18:38:13 +0000 Received: from parrot.netcom.co.uk ([217.72.171.49]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1Nrbed-0005m5-KO for rsgb_lf_group@blacksheep.org; Tue, 16 Mar 2010 18:38:13 +0000 Received: from abelian.netcom.co.uk (i-194-106-52-83.freedom2surf.net [194.106.52.83]) by parrot.netcom.co.uk (Postfix) with ESMTP id 4328B327822 for ; Tue, 16 Mar 2010 18:35:31 +0000 (GMT) Received: from [127.0.0.1] (localhost [127.0.0.1]) by abelian.netcom.co.uk (8.13.1/8.13.1) with ESMTP id o2GIc1LO002744 for ; Tue, 16 Mar 2010 18:38:03 GMT Message-ID: <4B9FD008.2070607@abelian.org> Date: Tue, 16 Mar 2010 18:38:00 +0000 From: Paul Nicholson User-Agent: Thunderbird 2.0.0.14 (X11/20080421) MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: In-Reply-To: X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: Ionospheric VLF propagation Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.9 required=5.0 tests=FROM_ENDS_IN_NUMS autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false x-aol-global-disposition: G x-aol-sid: 3039ac1d60ce4b9fd0521e83 X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) Alexander RA9MB wrote: > Fore large distanses i expect behaviour E ~ 1/sqrt(d). This would be the most straightforward explanation for the high signal strength. The signal expands with 1/r^2 power density and 1/r field strength until it is constrained by the Earth-ionosphere cavity, at say r = 100km. Thereafter, expansion is 1/r power density and 1/sqrt(r) field strength. For long distances, we can just assume 1/sqrt(r) field strength. We have then B = sqrt( 9.5e-21 * ERP/r) for a daytime D-layer at a height of 70km. For 1mW ERP over 850km, that gives 3.3fT which is a much better estimate than the 1/r^2. With multi-path interference, it could vary between zero and twice that figure. For conservation of energy, it cannot be higher than that, so that gives an upper bound. Then there must be the exponential factor for attenuation... -- Paul Nicholson --