Return-Path: X-Spam-DCC: paranoid 1233; Body=3 Fuz1=3 Fuz2=3 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 t6IDSV7q031533 for ; Sat, 18 Jul 2015 15:28:32 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZGS3Z-0005Xo-U5 for rs_out_1@blacksheep.org; Sat, 18 Jul 2015 14:21:33 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZGS3Z-0005Xf-EE for rsgb_lf_group@blacksheep.org; Sat, 18 Jul 2015 14:21:33 +0100 Received: from omr-m08.mx.aol.com ([64.12.222.129]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.85) (envelope-from ) id 1ZGS2V-00027h-BN for rsgb_lf_group@blacksheep.org; Sat, 18 Jul 2015 14:21:32 +0100 Received: from mtaout-aah01.mx.aol.com (mtaout-aah01.mx.aol.com [172.27.1.141]) by omr-m08.mx.aol.com (Outbound Mail Relay) with ESMTP id 75A6F704AD310 for ; Sat, 18 Jul 2015 09:20:08 -0400 (EDT) Received: from White (ipb21bee4a.dynamic.kabel-deutschland.de [178.27.238.74]) by mtaout-aah01.mx.aol.com (MUA/Third Party Client Interface) with ESMTPA id 7BF6238000091 for ; Sat, 18 Jul 2015 09:20:05 -0400 (EDT) Message-ID: From: "Markus Vester" To: References: <3EEE0BD431264721BAD95B0598D0A459@White> <55AA13A5.5090300@posteo.de> Date: Sat, 18 Jul 2015 15:20:24 +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=1437225608; bh=J2zSMd9crX49lSaX1lHorjUQ+YbXYHD4E7YmK6WZx8g=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=MayRZ3iSTj564iogRYIC0KBiAHz9sFAi/3IQ/1xncrRYn44INwl+EhkrLSRtnNw30 mnc1MqeqBoKgCzpEQoSEoepDnY16UFvYuGCzqMnsfPNBQAmzrtQaShoeJN7hsPUyPT txiCc44lgEQkZ+coaWGNTMGa4y7oz1Keyk5zh5KA= x-aol-sid: 3039ac1b018d55aa528517cb X-AOL-IP: 178.27.238.74 X-Scan-Signature: 986df75162af045670df2f67fcfcb92a Subject: Re: VLF: Tweek mode resonances Content-Type: multipart/alternative; boundary="----=_NextPart_000_000A_01D0C16D.44F29910" 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: 3663 Dies ist eine mehrteilige Nachricht im MIME-Format. ------=_NextPart_000_000A_01D0C16D.44F29910 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi Stefan, LF, we're not just playing around... I would rather consider this an = original scientific experiment, perhaps worth proposing as an research = project in environmental physics ;-) Frequency stability will not be much of an issue. Throughout the night, = the 5th order resonance moved around by two or three pixels, = approximately 100 Hz or twice its own width. So after having found the = right frequency in the first place, we could just let the transmitter = sit on the exact QRG for many hours without loosing much signal (even = more so for 1.7 kHz). Here are some back-of-the-envelope calculations for your institute = antenna, grounded at the other end: Assuming a loop area of around 2000 = m^2, radiation resistance at 8.5 kHz would be 0.17 microohms. Given the = cross section of your horizontal wire and the lightning protection = system, you could perhaps run up to 100 A loop current (maybe too = optimistic?), which would give 1.7 mW radiated power - comparable to = your first kite experiments and surely enough to be received here easily = even without any resonance enhancement. At 1.7 kHz, radiated power would = be 625 times smaller (2.6 uW) but probably still detectable under quiet = conditions. Estimated inductance would be around 110 uH or 5.9 j ohms at = 8.5 kHz. Depending on the quality of the grounding installation you will probably = require some kilowatts drive power, and a suitable array of parallel = FKP's to cancel inductance. Alternatively, the company I work for = produces some cool fat MRI gradient power amplifiers, designed to = deliver hundreds of amps into inductive loads ;-) On the receive side here, my biggest problem at low frequendcies is = railway interference - - this is one reason to start at higher frequency = before going to 1.7 kHz. As the incident wave will be circularly = polarized I could try to rotate the receive loop to minimize local QRM. = An interesting and favourable point is that your TX loop will be = pointing north-south, which will minimize "contamination" by direct = groundwave to my direction. However I do not know what the lateral = extent of the resonance mode is, in other words how much enhancement we = will still get at 180 km distance or 45=B0 elevation.=20 Alternatively you could try to detect the tweek resonance using your = garden receiver, close enough to provide true vertical skywave incidence = and full cavity resonance enhancement. To be able to see the skywave, = you will only have to turn the receive loop carefully to null direct = nearfield inductive coupling. One last point for dreamers: The counterrotating polarized component = which is not reflected will penetrate to the magnetosphere and may = propagate as a whistler wave. This could theoretically be received at = the magnetic conjugate point, somewhere near Madagascar... 73, Markus (DF6NM) =20 From: DK7FC=20 Sent: Saturday, July 18, 2015 10:51 AM To: rsgb_lf_group@blacksheep.org=20 Subject: Re: VLF: Tweek mode resonances Hello Markus, Thanks for your observation and article! :-) Most interesting. I can indeed confirm there were a number of cloud-cloud lightnings last = night, up to 20 per minute were visible at times. My VLF loop in the garden is a vertical hula hup circle with 80 turns of = wire inside. About 80 cm diameter. The receiver is the stereo soundcard, = making the stream for MF+VLF. This observation reminds me (of course) on our idea to try to transmit = (clap our hands!) on about 2 kHz, the 150 km band :-) with a vertical = loop and receive with a vertical loop! I should check if it is possible = to reach the roof of the other building, where my TX-antenna is mounted, = to ground the wire, i.e. to build a vertical loop! BTW, yesterday i officially requested a permission by the chief of the = local forest district to put some electronic equipment on a high tree in = the forest!! Solar, modules, batteries, WLAN-antenna and a box including = electronic equipment. The location is 3 km distant from the institute, = much more distant to man made noise sources then my garden and still in = a direct view to arrange the WLAN-link! No answer yet... The 5th mode near 8.5 kHz? Well, that resonance isn't really stable over = the frequency, so it is not possible to try modes like DFCW-6000 or even = 600. So the possible distances would be rather small. But woth to try = playing, obviously :-) 73, Stefan Am 18.07.2015 06:50, schrieb Markus Vester:=20 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 frequencies. 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 be 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_000A_01D0C16D.44F29910 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi Stefan, LF,
 
we're = not just=20 playing around... I would rather consider this an original = scientific=20 experiment, perhaps worth proposing as an research project in=20 environmental physics ;-)
 
Frequency stability will not be much of = an issue.=20 Throughout the night, the 5th order resonance moved around by two = or three=20 pixels, approximately 100 Hz or twice its own width. So after=20 having found the right frequency in the first place, we could just = let the=20 transmitter sit on the exact QRG for many hours without loosing much = signal=20 (even more so for 1.7 kHz).
 
Here = are some=20 back-of-the-envelope calculations for your institute antenna, grounded = at the=20 other end: Assuming a loop area of around 2000 m^2, radiation = resistance at=20 8.5 kHz would be 0.17 microohms. Given the cross section of = your=20 horizontal wire and the lightning protection system, you = could perhaps=20 run up to 100 A loop current (maybe too optimistic?), which would = give 1.7=20 mW radiated power - comparable to your first kite experiments and = surely=20 enough to be received here easily even without any resonance = enhancement. At 1.7=20 kHz, radiated power would be 625 times smaller (2.6 uW) but probably = still=20 detectable under quiet conditions. Estimated inductance would be = around 110=20 uH or 5.9 j ohms at 8.5 kHz.
 
Depending on the quality of the = grounding=20 installation you will probably require some kilowatts drive = power, and a=20 suitable array of parallel FKP's to cancel inductance. Alternatively, = the=20 company I work for produces some cool fat MRI gradient = power=20 amplifiers, designed to deliver hundreds of amps into inductive loads=20 ;-)
 
On the receive side here, my biggest problem at low = frequendcies is=20 railway interference - - this is one = reason to=20 start at higher frequency before going to 1.7 kHz. As the incident wave = will be=20 circularly polarized I could try to rotate the receive loop to = minimize=20 local QRM. An interesting and favourable point is that your TX loop will = be=20 pointing north-south, which will minimize "contamination" by = direct=20 groundwave to my direction. However I=20 do not know what the lateral extent of the resonance mode is, in = other=20 words how much enhancement we will still get at 180 km distance or 45=B0 = elevation.
 
Alternatively you could try=20 to detect the tweek resonance using your garden receiver, close = enough to=20 provide true vertical skywave incidence and full cavity resonance = enhancement.=20 To be able to see the skywave, you will only have to turn = the receive=20 loop carefully to null direct nearfield inductive = coupling.
 
One last point for dreamers: The = counterrotating=20 polarized component which is not reflected will penetrate to the = magnetosphere=20 and may propagate as a whistler wave. This could theoretically be = received=20 at the magnetic conjugate point, somewhere near = Madagascar...
 
73, Markus (DF6NM)

 
From:=20 DK7FC
Sent: Saturday, July 18, = 2015 10:51=20 AM
To: rsgb_lf_group@blacksheep.org=20
Subject: Re: VLF: Tweek = mode=20 resonances

Hello Markus,

Thanks for your = observation=20 and article! :-)
Most interesting.
I can indeed confirm there were = a=20 number of cloud-cloud lightnings last night, up to 20 per minute were = visible at=20 times.
My VLF loop in the garden is a vertical hula hup circle with = 80 turns=20 of wire inside. About 80 cm diameter. The receiver is the stereo = soundcard,=20 making the stream for MF+VLF.

This observation reminds me (of = course) on=20 our idea to try to transmit (clap our hands!) on about 2 kHz, the 150 km = band=20 :-) with a vertical loop and receive with a vertical loop! I should = check if it=20 is possible to reach the roof of the other building, where my TX-antenna = is=20 mounted, to ground the wire, i.e. to build a vertical loop!

BTW,=20 yesterday i officially requested a permission by the chief of the local = forest=20 district to put some electronic equipment on a high tree in the forest!! = Solar,=20 modules, batteries, WLAN-antenna and a box including electronic = equipment. The=20 location is 3 km distant from the institute, much more distant to man = made noise=20 sources then my garden and still in a direct view to arrange the = WLAN-link! No=20 answer yet...

The 5th mode near 8.5 kHz? Well, that resonance = isn't=20 really stable over the frequency, so it is not possible to try modes = like=20 DFCW-6000 or even 600. So the possible distances would be rather small. = But woth=20 to try playing, obviously :-)

73, Stefan

Am 18.07.2015 = 06:50,=20 schrieb Markus Vester:
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_G= rabber.html and was greeted by a fascinating display = on his VLF=20 panel.
 
The screenshot http://df6nm.bplaced.net/VLF/spherics/dk7fc_VLF_150718_1326.jpg<= /FONT> shows a number of narrow tweek-mode resonances at = multiples of=20 1.72 kHz. These are obviously spherics from nearby lightnings, bouncing = multiple=20 times vertically between the ionosphere and ground (much the same as = clapping=20 your hands between two parallel brick walls). The resonances are rather = sharp=20 indicating a high Q-number (ie. around 100 bounces until decay). = They are=20 visible up to about 20 kHz, showing unusually small damping of = vertical=20 incidence reflections at these frequencies. There is a small variation = of=20 resonance frequency over time, reflecting the variable height of the = ionospheric=20 ceiling. The fundamental resonance at 1.7 kHz is probably not = visible due=20 to the 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 the last red crosses between = Wiesbaden and=20 Stuttgart passing over Heidelberg at around 1:30.
 
The tweek resonances were received = on the loop=20 antenna in the garden but not on the E-field antenna of the = (somewhat=20 whitened out) city grabber http://df6nm.bplaced.net/VLF/spherics/dk7fc_wideband_150718_= 0330.jpg. This corroberates the notion of near vertical = incidence and=20 horizontal H-field polarisation. According to the literature, tweek = tails are=20 usually circular polarized as only one sense of rotation exhibits a high = reflection coefficient. They are predominately excited by horizontal = current=20 components in intra-cloud lightnings.
 
Of course the resonances will also = be there in=20 quiet nights without spherics, so they could probably be employed to=20 enhance fieldstrength (up to a factor of Q) for medium-range VLF=20 communication experiments using magnetic transmit and receive antennas. = When=20 Stefan still had his earth dipole we already discussed a 2 kHz = tweek-mode experiment, which for various reasons hasn't taken = place yet.=20 Now it looks like one could even employ the fifth mode near 8.5=20 kHz...
 
All the best,
Markus (DF6NM)
 
 
 
 
------=_NextPart_000_000A_01D0C16D.44F29910--