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 t2LCsVdg002669 for ; Sat, 21 Mar 2015 13:54:31 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1YZIsP-0002zo-W3 for rs_out_1@blacksheep.org; Sat, 21 Mar 2015 12:51:41 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1YZIsP-0002zf-Gz for rsgb_lf_group@blacksheep.org; Sat, 21 Mar 2015 12:51:41 +0000 Received: from omr-m02.mx.aol.com ([64.12.143.76]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.85) (envelope-from ) id 1YZIsM-0001Wa-HU for rsgb_lf_group@blacksheep.org; Sat, 21 Mar 2015 12:51:40 +0000 Received: from mtaout-aac02.mx.aol.com (mtaout-aac02.mx.aol.com [172.27.2.34]) by omr-m02.mx.aol.com (Outbound Mail Relay) with ESMTP id 08AF2700000B7; Sat, 21 Mar 2015 08:51:36 -0400 (EDT) Received: from Black (ipb21bee4a.dynamic.kabel-deutschland.de [178.27.238.74]) by mtaout-aac02.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id 0E4B63800008E; Sat, 21 Mar 2015 08:51:34 -0400 (EDT) Message-ID: <81A134ABA1A9478E88F4E77AF5166D80@Black> From: "Markus Vester" To: , References: <9CFA5B9805574BB082903B111F336D07@White> <816ADDCF03CD4A6E9ED49E63E4FC868A@Black> In-Reply-To: <816ADDCF03CD4A6E9ED49E63E4FC868A@Black> Date: Sat, 21 Mar 2015 13:51:33 +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=1426942295; bh=XuYdSFIybNWZVqwyXxO6q9HKPcza3x0kKbALnnXALNE=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=TnaFTIorUyaDo/aasQQIKx86ZdHJfwgZ7k2EIb3HA8E1Yx+aGnyXC9/7TykJBF7tF NwsDJywxYI37JNnMnSQ75kMnOiTJMNrPjT/B5mN/CRHTKyczm+jw+LA8iMemonJoyU IdJPEHImvdrLGTDXL/2PLHkhBQjMOR7BGllRS6U0= x-aol-sid: 3039ac1b0222550d69563c75 X-AOL-IP: 178.27.238.74 X-Scan-Signature: 94b4899eb522d3cd83a8c4d63d16b91e Subject: Re: LF: Radio Focussing by Solar Eclipse? Content-Type: multipart/alternative; boundary="----=_NextPart_000_000C_01D063DE.2448E170" 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: 2752 This is a multi-part message in MIME format. ------=_NextPart_000_000C_01D063DE.2448E170 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Peter, thanks for sharing this plot! The intense and well defined peak = would indeed suggest something like a focal point sweeping over the = receiver. The 1999 eclipse must have had almost ideal geometry, with the = moon's shadow crossing the middle of the path from Prangins to Kiel. Especially on longer paths, we may actiually have two distinct effects: = One is the decreasing D-layer absorption, opening the way to lossless = refraction in higher layers. This is surely also the explanation of the = "quasi-nighttime" boost of MF signals. On the other hand, there may be = that proposed lense-effect, creating a localized and moving focus point = for the reflection off the bottom layer conductivity gradient.=20 Taking another look at yesterday's 100 kHz plots = http://df6nm.bplaced.net/LoranView/eclipse/Loran_Eclipse_150320_plots.png= , we may actually find an indication for both effects: Three traces from = northerly stations (Jan Mayen, Eide, Bo) exhibit a large and = unsymmetrical hump (10 to 12 dB), beginning around 9:20 UT when the = penumbra begins to invade the North Sea. But on top of the Jan Mayen = hump there rides a little "hat", a small extra peak (~ 2 dB) at 9:53, = just when the central shadow crosses this path. No such thing appears on = the Ejde trace, and maybe a very small effect on Bo at 9:59. =20 I had first thought that the small peak was insignificant and might have = been caused by a solar flare, but there was none at the time. I would = now propose that the small peak is due to the focusing effect. In principle, arbitrary maxima and minima can also be caused by a = variable-phase skywave relative to a fixed groundwave; this has been = included in Micha's simulation. However at these much larger ranges = (2000 km and up), the groundwave contribution at 100 kHz is already = rather weak. In addition, Loran pulses are relatively wideband, and the = applied "total energy" postprocessing incoherently sums up differently = delayed pulse components, reducing the effect of relative phase. All the best, Markus (DF6NM) =20 =20 Peter DF3LP wrote: Mentioned in the article but not shown in this version: http://lf-radio.de/misc/eclipse/eclipse_1999.png The reason was, that I used a different method: selective level meter and DVM with serial output. 73 de df3lp, Peter ----- Original Message -----=20 From: Markus Vester=20 To: rsgb_lf_group@blacksheep.org ; rsgb_lf_group@yahoogroups.co.uk=20 Cc: pc4m@amsat.org=20 Sent: Saturday, March 21, 2015 9:28 AM Subject: LF: Radio Focussing by Solar Eclipse? 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_000C_01D063DE.2448E170 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Peter, thanks for sharing this = plot! The=20 intense and well defined peak would indeed suggest something like a = focal point=20 sweeping over the receiver. The 1999 eclipse must have had almost ideal=20 geometry, with the moon's shadow crossing the middle of = the path=20 from Prangins to Kiel.
 
Especially on longer paths, we may = actiually have=20 two distinct effects: One is the decreasing D-layer absorption, opening = the way=20 to lossless refraction in higher layers. This is surely = also the=20 explanation of the "quasi-nighttime" boost of MF signals. On the = other=20 hand, there may be that proposed lense-effect, creating a localized = and=20 moving focus point for the reflection off the bottom layer = conductivity=20 gradient.
 
Taking another look at yesterday's = 100 kHz=20 plots http://df6nm.bplaced.net/LoranView/eclipse/Loran_Eclipse_150320= _plots.png,=20 we may actually find an indication for both effects: Three traces from = northerly=20 stations (Jan Mayen, Eide, Bo) exhibit a large and unsymmetrical hump = (10 to 12=20 dB), beginning around 9:20 UT when the penumbra begins to = invade the=20 North Sea. But on top of the Jan Mayen hump = there rides a=20 little "hat", a small extra peak (~ 2 dB) at 9:53, just when the central = shadow=20 crosses this path. No such thing appears on the Ejde trace, and = maybe a=20 very small effect on Bo at 9:59.  
 
I had first thought that the small peak = was=20 insignificant and might have been caused by a solar flare, but there was = none at=20 the time. I would now propose that the small peak is due to the = focusing=20 effect.
 
In principle, arbitrary maxima and = minima can also=20 be caused by a variable-phase skywave relative to a fixed groundwave; = this has=20 been included in Micha's simulation. However at these much = larger=20 ranges (2000 km and up), the groundwave contribution at 100 kHz=20 is already rather weak. In addition, Loran pulses are relatively = wideband,=20 and the applied "total energy" postprocessing incoherently sums=20 up differently delayed pulse components, reducing the effect = of=20 relative phase.
 
All the best,
Markus (DF6NM)
 
 
Peter DF3LP wrote:

Mentioned in the article but not shown in this = version:
http://lf-radio= .de/misc/eclipse/eclipse_1999.png
The=20 reason was, that I used a different method:
selective level meter and = DVM=20 with serial output.

73 de df3lp,
Peter
----- Original Message -----=20
From: Markus = Vester=20
To: rsgb_lf_group@blacksheep.org= ; rsgb_lf_group@yahoogroups= .co.uk=20
Sent: Saturday, March 21, 2015 9:28 AM
Subject: LF: Radio Focussing by Solar Eclipse?

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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