Return-Path: X-Spam-DCC: paranoid 1233; 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 t6I4xoAx030919 for ; Sat, 18 Jul 2015 06:59:50 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZGK6H-0004h9-DR for rs_out_1@blacksheep.org; Sat, 18 Jul 2015 05:51:49 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZGK6G-0004h0-LC for rsgb_lf_group@blacksheep.org; Sat, 18 Jul 2015 05:51:48 +0100 Received: from omr-m4.mx.aol.com ([64.12.226.25]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.85) (envelope-from ) id 1ZGK5C-0000qO-Jc for rsgb_lf_group@blacksheep.org; Sat, 18 Jul 2015 05:51:47 +0100 Received: from mtaout-aac02.mx.aol.com (mtaout-aac02.mx.aol.com [172.27.2.34]) by omr-m4.mx.aol.com (Outbound Mail Relay) with ESMTP id A3BE238000098; Sat, 18 Jul 2015 00:50:24 -0400 (EDT) Received: from White (ipb21bee4a.dynamic.kabel-deutschland.de [178.27.238.74]) by mtaout-aac02.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id C784F38000089; Sat, 18 Jul 2015 00:50:21 -0400 (EDT) Message-ID: <3EEE0BD431264721BAD95B0598D0A459@White> From: "Markus Vester" To: , Date: Sat, 18 Jul 2015 06:50:43 +0200 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 12.0.1606 X-MimeOLE: Produced By Microsoft MimeOLE V12.0.1606 x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1437195024; bh=bXHSdSOLn48KJs3y7TwcVzE5Kd2GYCt3kMBxWZ+8x6k=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=MgIfJZS649obbYkgOpK/dqvNGDlCZi2rIm1lLRGMrMJh9gUVbv5AKhW6Z9YnhC/P0 DBsBjhFIZRH4YqCmJLWdI0QK4TBQ/uelpA/d5yKuYlCYTKQviv95JaizigHePUxoLu mdNkp7KMVbsL6etaUb/aI+wX+2oYG5r1qN6quWwk= x-aol-sid: 3039ac1b022255a9db0d6054 X-AOL-IP: 178.27.238.74 X-Scan-Signature: 4998b3eda037fec4e885bebc9a2db934 Subject: VLF: Tweek mode resonances Content-Type: multipart/alternative; boundary="----=_NextPart_000_0003_01D0C126.110E4410" 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: 3661 Dies ist eine mehrteilige Nachricht im MIME-Format. ------=_NextPart_000_0003_01D0C126.110E4410 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Waking up early this morning, I took a look at Stefan's garden grabber = http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_remote_Grabber.html = and was greeted by a fascinating display on his VLF panel.=20 The screenshot = http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150718_1326.jpg shows a = number of narrow tweek-mode resonances at multiples of 1.72 kHz. These = are obviously spherics from nearby lightnings, bouncing multiple times = vertically between the ionosphere and ground (much the same as clapping = your hands between two parallel brick walls). The resonances are rather = sharp indicating a high Q-number (ie. around 100 bounces until decay). = They are visible up to about 20 kHz, showing unusually small damping of = vertical incidence reflections at these ferequencies. There is a small = variation of resonance frequency over time, reflecting the variable = height of the ionospheric ceiling. The fundamental resonance at 1.7 kHz = is probably not visible due to the frequency response of the loop and = receiver. A (somewhat late) screenshot from Blitzortung = http://df6nm.bplaced.net/VLF/spherics/image_b_de_150718_0324.png shows = the last red crosses between Wiesbaden and Stuttgart passing over = Heidelberg at around 1:30. The tweek resonances were received on the loop antenna in the garden but = not on the E-field antenna of the (somewhat whitened out) city grabber = http://df6nm.bplaced.net/VLF/spherics/dk7fc_wideband_150718_0330.jpg. = This corroberates the notion of near vertical incidence and horizontal = H-field polarisation. According to the literature, tweek tails are = usually circular polarized as only one sense of rotation exhibits a high = reflection coefficient. They are predominately excited by horizontal = current components in intra-cloud lightnings. Of course the resonances will also there in quiet nights without = spherics, so they could probably be employed to enhance fieldstrength = (up to a factor of Q) for medium-range VLF communication experiments = using magnetic transmit and receive antennas. When Stefan still had his = earth dipole we already discussed a 2 kHz tweek-mode experiment, which = for various reasons hasn't taken place yet. Now it looks like one could = even employ the fifth mode near 8.5 kHz... All the best, Markus (DF6NM) ------=_NextPart_000_0003_01D0C126.110E4410 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Waking up early this morning, I took a = look at=20 Stefan's garden grabber http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_remote_Grabbe= r.html and=20 was greeted by a fascinating display on his VLF panel. =
 
The screenshot = http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150718_1326.jpg = shows a = number of narrow=20 tweek-mode resonances at multiples of 1.72 kHz. These are obviously = spherics=20 from nearby lightnings, bouncing multiple times vertically between the=20 ionosphere and ground (much the same as clapping your hands between two = parallel=20 brick walls). The resonances are = rather sharp=20 indicating a high Q-number (ie. around 100 bounces until decay).=20 They are visible up to about 20=20 kHz, showing unusually small damping of vertical incidence = reflections at=20 these ferequencies. There is a small variation of resonance frequency = over time,=20 reflecting the variable height of the ionospheric ceiling. The = fundamental=20 resonance at 1.7 kHz is probably not visible due to the frequency = response of=20 the loop and receiver.
 
A (somewhat late) screenshot from=20 Blitzortung http://df6nm.bplaced.net/VLF/spherics/image_b_de_150718_0324.png&nbs= p;shows=20 the last red crosses between Wiesbaden and Stuttgart passing = over=20 Heidelberg at around 1:30.
 
The tweek resonances were received on the loop antenna in the=20 garden but not on the E-field antenna of the (somewhat = whitened out)=20 city grabber http://df6nm.bplaced.net/VLF/spherics/dk7fc_wideband_150718_0330.jpg= .=20 This corroberates the notion of near vertical incidence and horizontal = H-field=20 polarisation. According to the literature, tweek tails are usually = circular=20 polarized as only one sense of rotation exhibits a high reflection = coefficient.=20 They are predominately excited by horizontal current components in = intra-cloud=20 lightnings.
 
Of course the resonances will also there in quiet nights = without=20 spherics, so they could probably be employed to = enhance fieldstrength (up=20 to a factor of Q) for medium-range VLF communication experiments using = magnetic=20 transmit and receive antennas. When Stefan still had his earth dipole=20 we already discussed a 2 kHz tweek-mode experiment, which for = various=20 reasons hasn't taken place yet. Now it looks like one could even = employ the=20 fifth mode near 8.5 kHz...
 
All the best,
Markus (DF6NM)
 
 
 
 
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