Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_40_50,HTML_MESSAGE autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id t2L8Vnio025745 for ; Sat, 21 Mar 2015 09:31:49 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1YZEle-0002So-JJ for rs_out_1@blacksheep.org; Sat, 21 Mar 2015 08:28:26 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1YZEld-0002Sf-SP for rsgb_lf_group@blacksheep.org; Sat, 21 Mar 2015 08:28:25 +0000 Received: from omr-m07.mx.aol.com ([64.12.143.81]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.85) (envelope-from ) id 1YZElb-0000n5-0p for rsgb_lf_group@blacksheep.org; Sat, 21 Mar 2015 08:28:24 +0000 Received: from mtaout-aao01.mx.aol.com (mtaout-aao01.mx.aol.com [172.27.21.13]) by omr-m07.mx.aol.com (Outbound Mail Relay) with ESMTP id 764A970035450; Sat, 21 Mar 2015 04:28:20 -0400 (EDT) Received: from Black (ipb21bee4a.dynamic.kabel-deutschland.de [178.27.238.74]) by mtaout-aao01.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id B95443800008B; Sat, 21 Mar 2015 04:28:19 -0400 (EDT) Message-ID: <816ADDCF03CD4A6E9ED49E63E4FC868A@Black> From: "Markus Vester" To: , Cc: References: <9CFA5B9805574BB082903B111F336D07@White> In-Reply-To: <9CFA5B9805574BB082903B111F336D07@White> Date: Sat, 21 Mar 2015 09:28:18 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Windows Mail 6.0.6002.18197 X-MimeOLE: Produced By Microsoft MimeOLE V6.0.6002.18463 x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20140625; t=1426926500; bh=JPYyhmdO7sskCR0vAEbPufsBKYtIVyOSxJEbf+UNf10=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=loUah53DC2v7HF+CjvOotKzuKItE/0cukM2rYOPGRvwvr/52HZ9j+Ru1er0JzHzAq gWQNWdlNhR9l/V1YNhZNEK58JbUpx3f+WJ7Be5WWs9/qJgZtCr4DCtocHSiXqtV3m9 9ZP4748hcPcZUQC+h9C5eBd11GnAeGHmBvsXyjhw= x-aol-sid: 3039ac1b150d550d2ba33e42 X-AOL-IP: 178.27.238.74 X-Scan-Signature: 1bc6486c2865e7dc2ff7578e6d7fc226 Subject: LF: Radio Focussing by Solar Eclipse? Content-Type: multipart/alternative; boundary="----=_NextPart_000_000E_01D063B9.5DC956C0" 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-Scanned-By: MIMEDefang 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 2749 This is a multi-part message in MIME format. ------=_NextPart_000_000E_01D063B9.5DC956C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Just came across at an excellent web paper by Micha Sanders (PC4M, = PA3BSH) http://misan.home.xs4all.nl/eclipse.htm, dealing with = observations of the HBG 75 kHz time signal during the 1999 solar = eclipse. Most observers found a characteristic W-shaped fieldstrength = curve, with a central maximum preceeded and followed by two minima. This = was found to agree very well with a simulation based on local D-layer = height variation around the moon's shadow. I've been wondering whether this couldn't be interpreted intuitively as = a focussing effect. An upward indent on the lower ionosphere could act = as a concave mirror, leading to convergence of radio waves into a focus = area, surrounded by a radio shadow. At lower VLF frequencies, we tend to think in two-dimensional waveguide = modes rather than vertically separated discrete rays. An analogous = interpretation would be an area of slower phase velocity near the center = of the eclipse, which would laterally bend radio waves towards a focus = area, acting very much like an optical lens. Best 73, Markus (DF6NM) ------=_NextPart_000_000E_01D063B9.5DC956C0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Just came across at an = excellent web paper by=20 Micha Sanders (PC4M, PA3BSH) http://misan.home.xs4all= .nl/eclipse.htm,=20 dealing with observations of the HBG 75 kHz time signal during the = 1999=20 solar eclipse. Most observers found a characteristic = W-shaped=20 fieldstrength curve, with a central maximum preceeded and followed by = two=20 minima. This was found to agree very well with a simulation based = on local=20 D-layer height variation around the moon's shadow.
 
I've been wondering whether = this couldn't be=20 interpreted intuitively as a focussing effect. An upward indent on = the=20 lower ionosphere could act as a concave mirror, leading to=20 convergence of radio waves into a focus area, surrounded = by a=20 radio shadow.
 
At lower VLF frequencies, we tend to = think in=20 two-dimensional waveguide modes rather than vertically separated = discrete=20 rays. An analogous interpretation would be an area of slower=20 phase velocity near the center of the eclipse,=20 which would laterally bend radio waves towards a focus = area,=20 acting very much like an optical lens.
 
Best 73,
Markus (DF6NM)
 
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