Return-Path: X-Spam-DCC: paranoid 1290; Body=2 Fuz1=4 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_MESSAGE,HTML_TINY_FONT,RATWARE_GECKO_BUILD,USER_IN_WHITELIST_TO 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 t6RALmQo027341 for ; Mon, 27 Jul 2015 12:21:49 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZJfTe-0001E6-2X for rs_out_1@blacksheep.org; Mon, 27 Jul 2015 11:17:46 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZJfTd-0001Dx-Bd for rsgb_lf_group@blacksheep.org; Mon, 27 Jul 2015 11:17:45 +0100 Received: from smtp-out01.xworks.net ([31.25.48.13]) by relay1.thorcom.net with esmtps (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.85) (envelope-from ) id 1ZJfSW-0000XT-44 for rsgb_lf_group@blacksheep.org; Mon, 27 Jul 2015 11:17:44 +0100 Received: from mailbackend3 (cluster06.xworks.net [10.100.1.80]) by smtp-out01.xworks.net (Postfix) with ESMTP id 044145F1AE; Mon, 27 Jul 2015 12:16:17 +0200 (CEST) X-DKIM-Result: Domain=kabelmail.de Result=Signature OK DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kabelmail.de; s=mail; t=1437992177; bh=WMMipDppz2IlvvSLcAuHNaSbtbNPA4/sAizTBshwcH0=; h=Date:From:MIME-Version:To:Subject:References:In-Reply-To: Content-Type; b=Wq/1Fxh2wocljDpTvqqJGe+Sx04liGDh2Sy318MTQOz9yj/s7kcYdVT0YdePvyBkl 1DcNOljL0Y3H/IofAyOyPKx6GhTo942gbnoJg1qnGM0ePlBx6Qp87/9djH5sI9AH8H Ek6MAw+81vaP7PQ7R0sLac830Gqm+g26gk3cDi8w= Received: from [192.168.178.33] (ipb21b5072.dynamic.kabel-deutschland.de [178.27.80.114]) (authenticated bits=0) by smtpa.mediabeam.com with ESMTP id t6RAGDaw009904 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 27 Jul 2015 12:16:14 +0200 X-mediaBEAM-Originating-IP: [178.27.80.114] X-mediaBEAM-AUTHID: [DK1IS@kabelmail.de] Message-ID: <55B604ED.3040709@kabelmail.de> Date: Mon, 27 Jul 2015 12:16:13 +0200 From: DK1IS User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: rsgb_lf_group@yahoogroups.co.uk, rsgb_lf_group@blacksheep.org, VLF_Group@yahoogroups.com References: <94D7BD8F8ABB4AB798759379C79927F3@White> In-Reply-To: <94D7BD8F8ABB4AB798759379C79927F3@White> X-mediaBEAM-AuthCheck: route13 X-mediaBEAM-AuthScore: 0.0/5.0, scanned in 1.941sec X-Scan-Signature: 417fb82f952d7d10264842fa503d685e Subject: Re: [rsgb_lf_group] Re: VLF: Tweek mode resonances Content-Type: multipart/alternative; boundary="------------000404000400090206000801" 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: 3711 This is a multi-part message in MIME format. --------------000404000400090206000801 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by smtpa.mediabeam.com id t6RAGDaw009904 Hello Markus, concerning the night from July 24 to 25 I can add that we had a heavy=20 thunderstorm with strong rain but only little wind here in JN59WK from=20 about 0005 UT to 0040 UT. Other than usual the lightnings had a=20 repetition time of only one or two seconds and *estimated 98% were=20 intra-cloud in high altitudes*, well above the lower border of the=20 clouds and more like sheet lightning despite the center of activity was=20 just above our QTH - very impressive! Have a look to=20 http://www.amberg-live.de/webcam/mariahilfberg1/#/2015/07/25/0455/thumb=20 , pictures from the webcam at our club station DL0AO, looking from=20 JN59VK to JN59WK. The time stamps are UT + 2 hours and you see a very=20 distributed glow of the sky in the range from 02:10 to 02:35 CEST. 73, Tom, DK1IS Am 27.07.2015 um 00:50 schrieb 'Markus Vester' markusvester@aol.com=20 [rsgb_lf_group]: > > Friday night (July 24/25) was stunning. Coming home from a beer after=20 > local midnight, I noticed spectacular VLF spherics resonances on the=20 > DK7FC remote garden grabber (screenshot=20 > http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150725_0704.jpg from=20 > the morning). I decided to restart the dual-loop directional=20 > spectrogram, the one which sometimes feeds my VLF wideband grabber. > After a couple of minutes, the first spectrum appeared, and I was=20 > literally swept away: Fat resonance peaks at all multiples of 1.62 kHz=20 > up to the tenth harmonic, and up to 20 dB above the noise:=20 > http://df6nm.bplaced.net/VLF/spherics/vlfwide_150725_0700_cursor-2347.p= ng.=20 > This was really surprising, as my suburban loops are usually very=20 > prone to local interference, and I had never seen or heard something=20 > like that before. The colour direction finder displayed the=20 > resonances in grey, which means "no direction", just as expected for a=20 > vertical-incidence circular polarized wave. > http://df6nm.bplaced.net/VLF/spherics/tweek_resonances_dk7fc_df6nm_Blit= zortung_150725_0700.png is=20 > a combined image showing two screenshots from Stefan in Heidelberg=20 > (top) and myself in Nuernberg (bottom), stacked above one another with=20 > identical timescales. The resonances in Heidelberg were strongest=20 > between 22 and 23 UT, became significantly weaker at 23:20, and died=20 > out about 0:10 UT. Resonances in Nuernberg came about an hour later,=20 > strongest at 23:40, and fadeout between 0:30 and 1:10=20 > UT. Interestingly, the resonance frequency goes through a flat minimum=20 > at the time of maximum amplitude and sharpness, which is different for=20 > the two locations. > The spectrograms can be compared to a Blitzortung screenshot taken at=20 > 0:40 UT, inserted at the bottom left of the image. Blitzortung sorts=20 > displayed flashes in 20 minute bins, indicated by colours from red=20 > (oldest, 22:40 - 23 UT), through shades of orange, to white (last 20=20 > minutes, i.e. 0:20 to 0:40 UT). For clarity, I repeated=20 > the Blitzortung colours in rectangles corresponding to the respective=20 > parts of the spectrogram timescale. > The position of the stormfront at the time of fadeout allows us to=20 > estimate the lateral range across which resonance amplification could=20 > be used to enhance communication. We find that tweek resonances were=20 > strong up to about 90 km away, and became very weak at about 180 km=20 > (indicated by blue circles around Heidelberg). Unfortunately this=20 > means that the distance between DK7FC and DF6NM (180 km) is probably=20 > already too large to benefit much from such a vertical resonance mode. > But on the other hand, it is known that tweeks have often been heard=20 > from great distances, up to 3000 or 6000 km over seawater. So why are=20 > the resonances restricted to a couple of 100 km? I think the answer=20 > for this is dispersion - the same effect that creates the=20 > characteristic chirp sound in distant tweeks. For a purely vertical=20 > wave, the time interval between successive hops is always 2h/c, about=20 > 0.6 ms with h =3D 90 km ionosphere height- This is the case if the=20 > source is close to the receiver. However at increased ranges, the=20 > path is initially at lower angle, and becomes steeper and steeper for=20 > later hops. Thus the time interval between successive pulses is=20 > initially smaller, and grows towards later (more vertical) hops.=20 > Source distance can be calculated from a tweek's knee in a spectrogram=20 > - far away sources have less rectangular, more rounded knees. In the=20 > resonance spectrum, this means that energy from for further away=20 > sources will be more spread out, and the maximum shifted to higher=20 > frequencies. This seems to be exactly what we have observed in the=20 > slow spectrograms: the sharpest resonances at the lowest frequencies=20 > occur when the storm passes just overhead. > At times, the resonances even appeared to split up. Look at the zoomed=20 > section around the fourth harmonic at the bottom: During the maximum=20 > in Nuernberg (23:45 UT), there are two distinct peaks, one at 6430 Hz=20 > and another at 6518 Hz. In the correponding orange Blitzortung=20 > crosses, we indeed find two separate sections of lightning activity, a=20 > smaller and nearer one passing south of Nuernberg, and another broader=20 > one passing north. > Let's take another look in time domain.=20 > http://df6nm.bplaced.net/VLF/spherics/dualloops_tweeks_scope.png are=20 > SpecLab scope shots from a couple of tweeks from recordings. For=20 > these, the frequency range had been restricted to 4 - 16 kHz to=20 > eliminate interference from 3 kHz railway noise and military MSK=20 > stations, and SpecLab's autonotch filter was engaged to=20 > suppress residual mains and railway harmonics. The two traces=20 > correspond to the two loops, red is the North-South loop (actually=20 > pointing 330=B0 azimuth), and blue is East-West (60=B0). Tweek #3 shows= a=20 > direct groundwave received only by the red channel, and a subsequent=20 > train of echoes which are received by both, with slightly increasing=20 > echo spacing. We find that undulations in the blue trace preceed those=20 > on the red one, showing that the circular polarized magnetic field=20 > vector rotates counterclockwise, i.e. from east to north. > There's also a couple of wav and ogg recordings in=20 > http://df6nm.bplaced.net/VLF/spherics/ - these nearby tweeks sound=20 > rather musical, like plucking on a short tight piece of guitar string. > All the best, > Markus (DF6NM) > PS: I started this thread on the rsgb LF reflector, but it may be=20 > appropriate to post to the VLF / Natural radio group guess I'll just=20 > do both. > *From:* Markus Vester > *Sent:* Saturday, July 18, 2015 6:50 AM > *To:* rsgb_lf_group@blacksheep.org=20 > ;=20 > rsgb_lf_group@yahoogroups.co.uk > *Subject:* VLF: Tweek mode resonances > > Waking up early this morning, I took a look at Stefan's garden grabber=20 > http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_remote_Grabber.html= and=20 > was greeted by a fascinating display on his VLF panel. > The screenshot=20 > http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150718_1326.jpg shows=20 > a number of narrow tweek-mode resonances at multiples of 1.72 kHz.=20 > These are obviously spherics from nearby lightnings, bouncing multiple=20 > times vertically between the ionosphere and ground (much the same as=20 > clapping your hands between two parallel brick walls). The resonances=20 > are rather sharp, indicating a high Q-number (ie. around 100 bounces=20 > until decay). They are visible up to about 20 kHz, showing unusually=20 > small damping of vertical incidence reflections at these frequencies.=20 > There is a small variation of resonance frequency over time,=20 > reflecting the variable height of the ionospheric ceiling. The=20 > fundamental resonance at 1.7 kHz is probably not visible due to the=20 > frequency response of the loop and receiver. > A (somewhat late) screenshot from Blitzortung=20 > http://df6nm.bplaced.net/VLF/spherics/image_b_de_150718_0324.png 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=20 > http://df6nm.bplaced.net/VLF/spherics/dk7fc_wideband_150718_0330.jpg.=20 > This corroberates the notion of near vertical incidence and horizontal=20 > H-field polarisation. According to the literature, tweek tails are=20 > usually circular polarized as only one sense of rotation exhibits a=20 > high reflection coefficient. They are predominately excited by=20 > horizontal current components in intra-cloud lightnings. > Of course the resonances will also be there in quiet nights without=20 > spherics, so they could probably be employed to enhance fieldstrength=20 > (up to a factor of Q) for medium-range VLF communication experiments=20 > using magnetic transmit and receive antennas. When Stefan still had=20 > his earth dipole, we already discussed a 2 kHz tweek-mode experiment,=20 > which for various reasons hasn't taken place yet. Now it looks like=20 > one could even employ the fifth mode near 8.5 kHz... > All the best, > Markus (DF6NM) > __._,_.___ > -----------------------------------------------------------------------= - > Posted by: "Markus Vester" > -----------------------------------------------------------------------= - > Reply via web post=20 > =20 > =95 Reply to sender=20 > =20 > =95 Reply to group=20 > =20 > =95 Start a new topic=20 > =20 > =95 Messages in this topic=20 > =20 > (3) > > Visit Your Group=20 > =20 > > > Yahoo! Groups=20 > =20 > > =95 Privacy=20 > =95=20 > Unsubscribe=20 > =20 > =95 Terms of Use=20 > > > . > > __,_._,___ --------------000404000400090206000801 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by smtpa.mediabeam.com id t6RAGDaw009904
Hello Markus,

concerning the night from July 24 to 25 I can add that we had a heavy thunderstorm with strong rain but only little wind here in JN59WK from about 0005 UT to 0040 UT. Other than usual the lightnings had a repetition time of only one or two seconds and = estimated 98% were intra-cloud in high altitudes, well above the lower border of the clouds and more like sheet lightning despite the center of activity was just above our QTH - very impressive! Have a look to http://www.amberg-live.d= e/webcam/mariahilfberg1/#/2015/07/25/0455/thumb , pictures from the webcam at our club station DL0AO, looking from JN59VK to JN59WK. The time stamps are UT + 2 hours and you see a very distributed glow of the sky in the range from 02:10 to 02:35 CEST.

73,
Tom, DK1IS


Am 27.07.2015 um 00:50 schrieb 'Markus Vester' markusvester@aol.com [rsgb_lf_group]:
=A0

Friday night (July 24/25= ) was stunning. Coming home from a beer after local midnight, I noticed spectacular VLF spherics resonances on the DK7FC remote garden grabber (screenshot http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150725_= 0704.jpg=A0from the morning). I decided to restart=A0the dual-loop directional spectrogram, the one=A0which sometimes feeds my VLF wideband grabber.
=A0
After a couple of minutes,=A0the first spectrum appeared, and=A0I was literally swept away: Fat resonance peaks=A0at all multiples of 1.62 kHz up to the tenth harmonic, and up to 20 dB above the noise: http://df6nm.bplaced.net/VLF/spherics/vlfwide_150725_0700_curso= r-2347.png. This was really surprising, as my suburban loops are usually very prone to local interference, and=A0I had never seen or heard something like that=A0before.=A0The colour direction finder displayed the resonances=A0in grey, which means=A0"no direction",=A0just as expected fo= r a vertical-incidence circular polarized wave.=A0
=A0
http://df6nm.bplaced.net/VLF/spherics/twee= k_resonances_dk7fc_df6nm_Blitzortung_150725_0700.png=A0is a combined image showing two screenshots from Stefan in Heidelberg (top) and myself in Nuernberg (bottom), stacked above one another=A0with identical=A0timescales. = The resonances in Heidelberg were strongest between 22 and 23 UT, became significantly weaker at 23:20, and died out about 0:10 UT. Resonances in Nuernberg came about an hour later, strongest=A0at 23:40,=A0and fadeout between 0= :30 and 1:10 UT.=A0Interestingly, the resonance frequency=A0g= oes through a flat minimum at=A0the time=A0of=A0maximum ampli= tude and sharpness,=A0which is different for the two locations= ..
=A0
The spectrograms=A0can b= e compared to a Blitzortung screenshot taken at 0:40 UT, inserted at the bottom left of the image. Blitzortung=A0<= /font>sorts displayed flashes=A0in 20 minute bins, indicated by colours from red (oldest, 22:40 - 23 UT), through shades of orange, to white (last 20 minutes,=A0i.e. 0:20 to 0:40 UT). For clarity, I repeated the=A0Blitzortung colours=A0in rectangles corresponding to the respective parts of the spectrogram timescale.
=A0
The position of the stormfront at the time of fadeout allows us to estimate the=A0lateral range across which resonance=A0amplificatio= n could be used to enhance communication. We find that tweek resonances=A0= were strong up to about=A090 km away, and became very weak at about 180 km (indicated by blue circles around Heidelberg). Unfortunately this means that=A0the distance between DK7FC and DF6NM (180 km) is probably already=A0to= o large=A0to benefit much from such a vertical resonance mode.
=A0
But on the other hand, i= t is known that tweeks=A0have=A0often been heard from great distances,=A0up to=A03000 or 6000 km over seawater.=A0So = why are the=A0resonances restricted to a couple of 100 km?=A0= I think the answer for this is=A0dispersion - the same effect that creates the characteristic chirp sound in distant tweeks. For=A0a purely vertical wave, the time interval between successive=A0hops is always 2h/c, about 0.6 ms with h =3D= 90 km ionosphere height- This is the case if the source is close to the receiver. However at increased ranges, the path=A0is initially at lower angle, and becomes steeper and steeper for later hops. Thus the time interval between successive pulses is initially smaller, and grows towards later (more vertical) hops. Source distance can be calculated from a tweek's knee in a spectrogram -=A0fa= r away sources=A0have less rectangular, more rounded knees.= =A0In the resonance spectrum, this means that=A0energy from for further away sources will be more spread out, and the maximum shifted to higher frequencies. This seems to be=A0exactly what we=A0have observed in the slow spectrograms:=A0the sharpest resonances at the lowest frequencies occur when the storm passes just overhead.
=A0
At times, the resonances=A0even appeared to=A0split up.=A0Look at the z= oomed section around the fourth harmonic at the bottom: During the maximum in Nuernberg (23:45 UT), there are two distinct peaks, one at =A06430 Hz and another at 6518 Hz.=A0In the correponding orange Blitzortung crosses,=A0w= e indeed=A0find two separate sections of lightning activity= , a smaller and nearer one passing south of Nuernberg, and=A0another broader one passing north.
=A0
Let's take another look = in time domain. http://df6nm.bplaced.net/VLF/spherics/dualloops_tweeks= _scope.png=A0are SpecLab scope shots from a couple of tweeks from recordings. For these, the frequency range had been restricted to=A04=A0- 16 kHz to eliminate=A0interference = from 3 kHz railway noise and military MSK stations,=A0and SpecLab's autonotch filter was engaged to suppress=A0residual mains and railway harmonics.=A0The tw= o traces correspond to the two loops, red is the North-South loop (actually pointing 330=B0 azimuth), and blue is East-West=A0(60=B0). Tweek #3 shows a direct groundwave received only by the red channel, and a subsequent train of echoes which are received by both, with slightly increasing echo spacing. We find that undulations in the blue trace preceed those on the red one,=A0showing that the circular polarized magnetic field vector=A0rotates counterclockwise,=A0i.e. from east to north.
=A0
There's also a couple of wav and ogg recordings in http://= df6nm.bplaced.net/VLF/spherics/=A0- these nearby tweeks sound rather musical, like plucking on a short tight piece of guitar string.
=A0
All the best,
Markus (DF6NM)
=A0
PS: I started this threa= d on the rsgb LF reflector, but it may be appropriate to post=A0to the VLF / Natural radio group=A0 guess I'll jus= t do both.
=A0
=A0

Waking up early this morning, I took a look at Stefan's garden grabber http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_remote_Grabbe= r.html=A0and was greeted by a fascinating display on=A0his VLF panel. =
=A0
The screenshot http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150718_= 1326.jpg=A0shows=A0a 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=A0are visible up to about 20 kHz,=A0showing unusually small damping of vertical incidence reflections at these frequencies. There is a small variation of resonance frequency over time, reflecting the variable height of the ionospheric ceiling.=A0The fundamental resonance at 1.7 kHz is probably not visible due to the frequency response of the loop and receiver.
=A0
A=A0(somewhat late) screenshot from Blitzortung=A0http://df6nm.bplaced.net/VLF/spherics/image_b_de_150= 718_0324.png=A0shows the last red=A0crosses between Wiesbaden and Stuttgart=A0passing over Heidelberg at around 1:30.
=A0
The=A0tweek resonances were received on the loop antenna in the garden=A0but not=A0on 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.<= /div>
=A0
Of course the resonances will=A0also be there in quiet nights without spherics, so they could probably be employed to enhance=A0fieldstrength (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=A0already discussed a=A02 = kHz tweek-mode experiment, which for various reasons hasn't taken place=A0yet. Now it looks like one could even emplo= y the fifth mode near 8.5 kHz...
=A0
All the best,
Markus (DF6NM)
=A0
__._,_.___
Posted by: "Markus Vester" <markusvester@aol.com>
Reply via web post =95 Reply to sender =95 Repl= y to group =95 Start a new topic =95 Mess= ages in this topic (3)

.

__,_._,___

--------------000404000400090206000801--