Return-Path: Received: from mtain-de01.r1000.mx.aol.com (mtain-de01.r1000.mx.aol.com [172.29.64.201]) by air-di03.mail.aol.com (v127_r1.1) with ESMTP id MAILINDI031-eabe4b9bcd143c4; Sat, 13 Mar 2010 12:36:20 -0500 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by mtain-de01.r1000.mx.aol.com (Internet Inbound) with ESMTP id 09AD93800008E; Sat, 13 Mar 2010 12:36:18 -0500 (EST) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1NqVEh-0005CS-Bo for rs_out_1@blacksheep.org; Sat, 13 Mar 2010 17:34:51 +0000 Received: from [193.82.116.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1NqVEg-0005CJ-Rm for rsgb_lf_group@blacksheep.org; Sat, 13 Mar 2010 17:34:50 +0000 Received: from mail-bw0-f215.google.com ([209.85.218.215]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1NqVEd-00039S-Me for rsgb_lf_group@blacksheep.org; Sat, 13 Mar 2010 17:34:50 +0000 Received: by bwz7 with SMTP id 7so1923627bwz.4 for ; Sat, 13 Mar 2010 09:34:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=Fbl1kkcO5fpvpNTatZCVP+bXXA98hNaFVgd8PgSk4D8=; b=vBA84jmF/siDN1YP4CNgIUX64wlXfsYqYQCfO9OFHOiFRPjjfj0bEl2mvA/g//OgAc lzJyrsQxVhdTOWg/BMXl5Ls7OB6iFHaRn0Toxz0W9Jv2nQ7Cujf0ZJMR9XBBpEa6XQ4F IC0r8pkAF1tpzs/IDBZ5YxjeplkpMtSIADcJU= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=kYXdQfL4CjYgw/2Izlxndvbskko3xX2p3ECbzqrXtNQh3IW66Vbmvsw6OtTskDMEuu hWPNbJn9AdEKRfsMzcQitxme5Yz79gOeEB1ee6KgYEAUjUbBKFDP3Gtu7o6xHj3dbW0S MRd9O6Cd96EAa4S2lj/L0ks4syr9Gk6upPJxo= MIME-Version: 1.0 Received: by 10.204.156.211 with SMTP id y19mr582779bkw.57.1268501681839; Sat, 13 Mar 2010 09:34:41 -0800 (PST) In-Reply-To: <9afca2641003111254v47a0363eicdee899d7c2b3431@mail.gmail.com> References: <9afca2641003111254v47a0363eicdee899d7c2b3431@mail.gmail.com> Date: Sat, 13 Mar 2010 17:34:41 +0000 Message-ID: <9afca2641003130934g7e13a091vd2a445d8284e5cd@mail.gmail.com> From: Roger Lapthorn To: rsgb_lf_group@blacksheep.org DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: LF: Re: Induction DX? Content-Type: multipart/alternative; boundary=0015175d01ee249f8e0481b21083 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.1 required=5.0 tests=HTML_FONTCOLOR_UNSAFE, HTML_MESSAGE autolearn=no version=2.63 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-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m209.1 ; domain : gmail.com DKIM : fail x-aol-sid: 3039ac1d40c94b9bcd12099e X-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) --0015175d01ee249f8e0481b21083 Content-Type: text/plain; charset=ISO-8859-1 Thanks for all the responses so far on this. One interesting factor which applies both to induction and earth mode (conduction) communication at VLF is the inverse cube law for attenuation. The upside of this is that if you are only trying to cover much more modest distances (1-2kms say) then the power needed is a LOT less than that to achieve twice this range or to try for DX by true radiation. Clearly there ends up being two distinct groups here (a) those who will be using lots of power and big antennas who should be able to get some useful amount of RF radiated below 9kHz and who have a chance of spanning some significant distances (possibly hundreds of kms), and (b) those using far more modest power levels who will only realistically be able to transmit by conduction or induction over quite local ranges. Although I shall be in the latter group because of my very limited garden size I'll be more than willing to try to *receive* stations seriously attempting real distance sub-9kHz. Personally, I've quite enjoyed this whole area of discussion. 73s Roger G3XBM On 11 March 2010 20:54, Roger Lapthorn wrote: > *If I've asked this before please forgive me....* > > With all the discussion recently on how to* radiate* a signal on sub-9kHz > I'm left wondrering how far, practically, one could expect to get simply > with sub-9kHz magnetic induction using multi-turn loops at each end? The > Cave Radio Group (CREG) may have some answers but I'm not a subscriber so > can't read any of their documents. > > It would be quite easy for anyone to generate 50-100W or so and feed this > into a largish diameter multi-turn loop. Correctly aligned and with a > similar loop at the far end and using decent weak signal processing just > what range might be possible using modes like QRSS or WSPR? Has anyone tried > this to see just what is practical, simply using induction fields? > > Also, can anyone point me to some webpages with some practical audio > frequency induction communication systems? There are lots of references to > near field comms for on-body and inter-device comms but I've not found much > otherwise. > > 73s > Roger G3XBM > > > -- > http://g3xbm-qrp.blogspot.com/ > http://www.g3xbm.co.uk > http://www.youtube.com/user/G3XBM > G3XBM GQRP 1678 ISWL G11088 > -- http://g3xbm-qrp.blogspot.com/ http://www.g3xbm.co.uk http://www.youtube.com/user/G3XBM G3XBM GQRP 1678 ISWL G11088 --0015175d01ee249f8e0481b21083 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Thanks for all the responses so far on this.

One interesting facto= r which applies both to induction and earth mode (conduction) communicatio= n at VLF is the inverse cube law for attenuation. The upside of this is th= at if you are only trying to cover much more modest distances (1-2kms say)= then the power needed is a LOT less than that to achieve twice this range= or to try for DX by true radiation.

Clearly there ends up being two distinct groups here (a) those who wil= l be using lots of power and big antennas who should be able to get some= useful amount of RF radiated below 9kHz and who have a chance of spanning= some significant distances (possibly hundreds of kms), and (b) those usin= g far more modest power levels who will only realistically be able to tran= smit by conduction or induction over quite local ranges. Although I shall= be in the latter group because of my very limited garden size I'll be= more than willing to try to receive stations seriously attempting= real distance sub-9kHz.

Personally, I've quite enjoyed this whole area of discussion.
<= br>73s
Roger G3XBM

On 11 March 2010= 20:54, Roger Lapthorn <rogerlapthorn@gmail.com> wrote:
If I've= asked this before please forgive me....

With all= the discussion recently on how to radiate a signal on sub-9kHz I&#= 39;m left wondrering how far, practically, one could expect to get simply= with sub-9kHz magnetic induction using multi-turn loops at each end?=A0= The Cave Radio Group (CREG) may have some answers but I'm not a subsc= riber so can't read any of their documents.

It would be quite easy for anyone to generate 50-100W or so and feed= this into a largish diameter multi-turn loop. Correctly aligned and with= a similar loop at the far end and using decent weak signal processing jus= t what range might be possible using modes like QRSS or WSPR? Has anyone= tried this to see just what is practical, simply using induction fields?=

Also, can anyone point me to some webpages with some practical audio= frequency induction communication systems? There are lots of references= to near field comms for on-body and inter-device comms but I've not= found much otherwise.

73s
Roger G3XBM


--
http://g3xbm-qrp.blo= gspot.com/
htt= p://www.g3xbm.co.uk
http://www= .youtube.com/user/G3XBM
G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088



--

http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/G3XBM G3XBM =A0 =A0GQRP 1678 =A0 =A0 =A0ISWL G11088
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