Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=5.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE,RCVD_IN_DNSWL_MED, SPF_PASS,T_DKIM_INVALID autolearn=ham autolearn_force=no version=3.4.0 X-Spam-DCC: EATSERVER: mailn 1166; Body=2 Fuz1=2 Fuz2=2 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by lipkowski.org (8.14.4/8.14.4/Debian-8+deb8u1) with ESMTP id v23IQxs5029062 for ; Fri, 3 Mar 2017 19:27:00 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1cjrlx-0008CW-Pm for rs_out_1@blacksheep.org; Fri, 03 Mar 2017 18:17:45 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1cjrls-0008CN-Uv for rsgb_lf_group@blacksheep.org; Fri, 03 Mar 2017 18:17:40 +0000 Received: from omr-a014e.mx.aol.com ([204.29.186.62]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.87) (envelope-from ) id 1cjrlo-0000Fq-Q3 for rsgb_lf_group@blacksheep.org; Fri, 03 Mar 2017 18:17:39 +0000 Received: from mtaomg-laa01.mx.aol.com (mtaomg-laa01.mx.aol.com [172.27.2.99]) by omr-a014e.mx.aol.com (Outbound Mail Relay) with ESMTP id A309B38000A6 for ; Fri, 3 Mar 2017 13:17:34 -0500 (EST) Received: from core-acb01e.mail.aol.com (core-acb01.mail.aol.com [172.27.24.1]) by mtaomg-laa01.mx.aol.com (OMAG/Core Interface) with ESMTP id 2315C38000088 for ; Fri, 3 Mar 2017 13:17:34 -0500 (EST) Received: from 188.192.95.60 by webprd-m71.mail.aol.com (10.74.55.19) with HTTP (WebMailUI); Fri, 03 Mar 2017 13:17:33 -0500 Date: Fri, 3 Mar 2017 13:17:33 -0500 From: Markus Vester To: rsgb_lf_group@blacksheep.org Message-Id: <15a9564290d-44c1-ab3f@webprd-m71.mail.aol.com> In-Reply-To: References: MIME-Version: 1.0 X-MB-Message-Source: WebUI X-MB-Message-Type: User X-Mailer: JAS STD X-Originating-IP: [188.192.95.60] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1488565054; bh=6QMLGaMMSqE2yAxoIhXbpkXCZtTChSr67jBkcN+wCVk=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=JWrNRAcRQkUmlI0bWNbK6htsof+u1aYmGJ9I/2muPIm1eyOYzMIlzKKl4x8HVYwOL R5k6nmHpnopLxHf50X3yTcSBK7kwGRkKiDICWa7fA99mH1tSMLmO7NtZu5l7yR1/gV PE8vNRQbp9I+uQZVDxcfm20zAFlcfqs50uH81+Kw= x-aol-sid: 3039ac1b026358b9b33e5428 X-Scan-Signature: 09c1a181dc7b5fd4ce37590584a561d1 Subject: Re: LF: phase shift compensation question - and the moon Content-Type: multipart/alternative; boundary="----=_Part_54083_367697868.1488565053706" 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 2.75 Status: RO X-Status: X-Keywords: X-UID: 10769 ------=_Part_54083_367697868.1488565053706 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Jacek, this is an interesting question. At VLF frequencies and over long distances, diurnal phase patterns seem to = be pretty regular and repeatable so they could be predicted by calculation.= At higher frequencies and intermediate ranges, the situation is complicate= d by multipath / multimode propagation, producing more random phase and fad= ing patterns. As you say, the phase effects could still be compensated usin= g a pilot signal, provided that the frequency and the geometrical path are = similar. But how close would they need to be "similar", or in other words, = what is the temporal and spatial coherence width of a wavefront?=20 I have been observing Loran-C stations for many years, and I believe that t= hese data could provide sonme insight. At night, the impulse response cons= ists of a number of differently delayed skywave components. Most of the ene= rgy is contained within about a millisecond, indicating coherent fading pat= terns over frequencies deviations up to about a kHz. The question of spatia= l correlation is a bit harder as we have only sparse data from a limited nu= mber of locations. Until 2010, an interesting example were three stations i= n the Newfoundland chain (Fox Harbour, Comfort Cove and Cape Race, GRI 7930= ), which are a few hundred km apart and used to have very similar looking i= mpulse responses: http://df6nm.bplaced.net/LoranView/LoranView_1002.htm . O= n the other hand, the signal from Caribou ~1000 km further away already sho= wed a quite different pattern. BTW unfortunately DCF39 would not be a good pilot, as the frequency drifts = quite a bit, and the carrier is spread by phase jumps from the FSK telegram= s. HGA22 seems to be intrinsically more stable (a few ppb), but it is also = contaminated by the same modulation. Another interesting application could be unspreading VHF EME signals. Weak = signal reception over the moon could be much improved if long coherent inte= gration times could be used. But this is limited to about a second by libra= tion spreading, caused by the superposition of many scattering centers on t= he lunar surface. The complex sum is highly dependent on the view angle, wh= ich varies over time because TX and RX both move with earth's rotation, and= also to a lesser degree due to the excentric and tilted lunar orbit.=20 However unlike ionospheric fading, the associated speckle pattern is rather= deterministic, literally "carved in stone". So in principle if we had coll= ected a database of a priori measurements of phase factors for all accessib= le aspect angles, we could predict and undo the phase evolution and then us= e arbitrarily long integration and small noise bandwidth. However this data= base would need to be quite large (~ 10^10 viewangles at 144 MHz). On the other hand, noticing that earth is moving beneath a fixed speckle pa= ttern, the same fading pattern would be repeated to an observer further wes= t some minutes or hours later. Thus we could possibly use a CW signal from = a big gun as a pilot, and then apply a delayed version of the conjugate pha= se to receive a weak station located on the same latitude but further west. Best 73, Markus =20 -----Urspr=C3=BCngliche Mitteilung-----=20 Von: Jacek Lipkowski An: rsgb_lf_group Verschickt: Fr, 3. Mrz 2017 15:12 Betreff: LF: phase shift compensation question would it be possible to use the phase shift from a strong VLF signal to=20 compensate the phase shift for an amateur VLF transmitter? for longer=20 transmissions (when the ionosphere height changes etc) over big distances= =20 etc could also work for LF, like receiving DCF39 (which is probably very=20 stable, even if it's not intended for timing) on 139kHz in Australia to=20 measure the phase shift of the path from Germany, so that we can=20 compensate the changing phase shift of an amateur transmission on 137kHz,= =20 so that we could use a long transmission time in ebnaut. would that work? and would it be worth it? VY 73 Jacek / SQ5BPF ------=_Part_54083_367697868.1488565053706 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Hi Jacek,
this is an interesting qu= estion.
At VLF frequencies and over long distances, di= urnal phase patterns seem to be pretty regular and repeatable so they could= be predicted by calculation. At higher frequencies and intermediate ranges= , the situation is complicated by multipath / multimode propagation, produc= ing more random phase and fading patterns. As you say, the phase effects co= uld still be compensated using a pilot signal, provided that the frequency = and the geometrical path are similar. But how close would they need to be "= similar", or in other words, what is the temporal and spatial coherence wid= th of a wavefront?
I have been observing Loran-C stat= ions for many years, and I believe that these data could provide sonme insi= ght. At night, the  impulse response consists of a number of different= ly delayed skywave components. Most of the energy is contained within about= a millisecond, indicating coherent fading patterns over frequencies deviat= ions up to about a kHz. The question of spatial correlation is a bit harder= as we have only sparse data from a limited number of locations. Until 2010= , an interesting example were three stations in the Newfoundland chain (Fox= Harbour, Comfort Cove and Cape Race, GRI 7930), which are a few hundred km= apart and used to have very similar looking impulse responses: http://df6n= m.bplaced.net/LoranView/LoranView_1002.htm . On the other hand, the signal = from Caribou ~1000 km further away already showed a quite different pattern= .
BTW unfortunately DCF39 would not be a good pilot, a= s the frequency drifts quite a bit, and the carrier is spread by phase jump= s from the FSK telegrams. HGA22 seems to be intrinsically more stable (a fe= w ppb), but it is also contaminated by the same modulation.

However unlike ionospheric fading, the associate= d speckle pattern is rather deterministic, literally "carved in stone". So = in principle if we had collected a database of a priori measurements of pha= se factors for all accessible aspect angles, we could predict and undo the = phase evolution and then use arbitrarily long integration and small noise b= andwidth. However this database would need to be quite large (~ 10^10 viewa= ngles at 144 MHz).

On the other hand, noticing that ea= rth is moving beneath a fixed speckle pattern, the same fading pattern woul= d be repeated to an observer further west some minutes or hours later. Thus= we could possibly use a CW signal from a big gun as a pilot, and then appl= y a delayed version of the conjugate phase to receive a weak station locate= d on the same latitude but further west.

Best 73,
M= arkus  




-----Urspr=C3=BCngliche= Mitteilung-----
Von: Jacek Lipkowski <sq5bpf@lipkowski.org>
A= n: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 3.= Mrz 2017 15:12
Betreff: LF: phase shift compensation question

would it be possible to use the phase shift from a strong VLF signal to=
compensate the phase shift for an amateur VLF transmitter? for longer =
transmissions (when the ionosphere height changes etc) over big distanc= es
etc

could also work for LF, like receiving DCF39 (which is pr= obably very
stable, even if it's not intended for timing) on 139kHz in = Australia to
measure the phase shift of the path from Germany, so that = we can
compensate the changing phase shift of an amateur transmission o= n 137kHz,
so that we could use a long transmission time in ebnaut.
<= br>would that work? and would it be worth it?

VY 73

Jacek / S= Q5BPF


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